Temat: 74.20.+z - Katalog OPAC zbiorów

Skocz do pozycji: 1.

Tytuł:: Thermodynamic Properties of D-Wave Paired Superconductors
Autorzy:: Gonczarek, R.
Mulak, M.
Kumala, W.
Powiązania:: https://bibliotekanauki.pl/articles/1994689.pdf
Data publikacji:: 1999-02
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
Opis:: The D-wave paired Fermi system is considered in the frame of generalized gap equation obtained in a BCS-like approach. It is shown that the thermodynamic functions of a system, as the thermodynamic potential, entropy and heat capacity differences between the normal and superconducting state are precisely defined functionals of the energy gap as a function of temperature. The derived formulas are identical as those obtained for S-wave paired Fermi system. It states that the developed formalism can be applied, in practice, to investigation of real superconductors in which a singlet state is realized. Some numerical results illustrating prospects and capabilities of the presented formalism are given for chosen structures of the order parameter.
Źródło:: Acta Physica Polonica A; 1999, 95, 2; 231-242
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 2.

Tytuł:: Superconductivity of the Weak Hopping Anderson Lattice with Generalized Electron Interactions
Autorzy:: Trieu, Duong Hai
Powiązania:: https://bibliotekanauki.pl/articles/1891689.pdf
Data publikacji:: 1991-10
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
Opis:: We study the Anderson lattice with a weak hopping amplitude t and generalized electron interactions. The interactions between f electrons, between f and conduction electrons and between conduction electrons are taken into account. An effective Hamiltonian in a second order perturbation in t is derived. Using this Hamiltonian, we study superconductivity. Singlet d-like superconductivity may occur in presence of the above interactions. In some cases the interactions lead to suppressing superconductivity.
Źródło:: Acta Physica Polonica A; 1991, 80, 4; 601-610
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 3.

Tytuł:: Parametric Equations for the Energy Gap. Extended BCS Case
Autorzy:: Gonczarek, R.
Mulak, M.
Powiązania:: https://bibliotekanauki.pl/articles/1931831.pdf
Data publikacji:: 1994-12
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
Opis:: The generalised form of the gap equation which comprises also some non-BCS approaches is defined and solved. The parametric gap equations have been derived in a few equivalent cases and discussed in$\text{}_{}$dissimilar limits. It is shown that the relations between the critical temperature and zero-temperature energy gap can be extended for all systems under consideration. The main benefits and incontestable advantage of the presented method are demonstrated with regard to the general BCS case.
Źródło:: Acta Physica Polonica A; 1994, 86, 6; 1007-1014
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 4.

Tytuł:: Thermodynamic Properties of D-Wave Paired Superconductors in the Low Temperature and Subcritical Regions
Autorzy:: Kumala, W.
Gonczarek, R.
Mulak, M.
Powiązania:: https://bibliotekanauki.pl/articles/2013257.pdf
Data publikacji:: 2000-04
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
Opis:: D-wave paired isotropic Fermi system in the limiting cases T → T$\text{}_{c}$ and T → 0 is considered. Values of the energy gap, the thermodynamic potential, and the specific heat as a function of temperature are given for admissible solutions and compared with values for S-wave paired system. It is shown that the linear term of low temperature specific heat vanishes likewise in case of S-wave pairing. The obtained results make prospects to define the geometry of the energy gap in virtue of the behavior of the specific heat in the limiting temperature cases for heavy-fermion superconductors.
Źródło:: Acta Physica Polonica A; 2000, 97, 4; 693-703
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 5.

Tytuł:: The Form of Energy Gap and Critical Temperature of Superconductor Implied by Fluctuations of Density of States
Autorzy:: Gładysiewicz, M.
Gonczarek, R.
Mulak, M.
Powiązania:: https://bibliotekanauki.pl/articles/2014021.pdf
Data publikacji:: 2000-06
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
Opis:: The s-paired BCS superconductor with the electron density of states depending on energy in the vicinity of Fermi level is considered. The existence of such fluctuations of electron density of states may be referred to Van Hove singularities widely discussed in the literature. In the paper three types of small fluctuations of the electron density of states introduced about its average background's value are analysed: Lorentzian, triangle, and logarithmic ones. In order to calculate numerically the energy gap and critical temperature, the formalism of parametric BCS gap equations is applied. The positive fluctuations (peaks) correspond to the increase in occupied states number inducing a higher critical temperature. On the other hand, negative fluctuations, which decrease the number of occupied states, lead to a lower critical temperature. Such decrease in critical temperature can lead, at a specific choice of parameters, to the decease in superconductivity. The presence of fluctuations finds reflection in the shape of energy gap as a function of temperature. In the vicinity of T=0 an abrupt decrease or increase in the energy gap to the original BCS value, according to the sign of the fluctuation, is observed. In turn, the fluctuations do not change the behaviour of the energy gap near T$\text{}_{c}$.
Źródło:: Acta Physica Polonica A; 2000, 97, 6; 1039-1051
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 6.

Tytuł:: On the Crossover from BCS Superconductivity to Bose Condensation
Autorzy:: Micnas, R.
Powiązania:: https://bibliotekanauki.pl/articles/2030399.pdf
Data publikacji:: 2001-12
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
Opis:: We outline a microscopic approach to the superconducting fluctuations and pairing correlations in the attractive Hubbard model above T$\text{}_{c}$, using the functional integral method. A crossover from BCS superconductivity to Bose condensation of preformed pairs is studied by constructing the appropriate Ginzburg-Landau functionals. The differences between the lattice and the continuum models are discussed. The case of quasi-two-dimensional superconductors as well as the model with non-local pairing interaction are also examined. The effects of Gaussian fluctuations of the order parameter are analyzed in the T-matrix approach, the self-consistent Hartree approach and finally within the Ginzburg-Landau theory. Similarities with a paramagnon theory of itinerant-electron magnetism are pointed out.
Źródło:: Acta Physica Polonica A; 2001, 100, Supplement; 177-194
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 7.

Tytuł:: Discontinuous Phase Transitions in S-Paired Fermi Systems
Autorzy:: Mulak, M.
Gonczarek, R.
Powiązania:: https://bibliotekanauki.pl/articles/1968488.pdf
Data publikacji:: 1997-12
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
Opis:: The most general S-paired systems of fermions for which a gap equation can be separated according to the specific redefined variables, are considered. Moreover, a solution of this gap equation (gap energy) is obtained in a parametric form. It allows us to investigate thermodynamic properties of such systems i.e. the thermodynamic potential, entropy, heat capacity and critical magnetic induction. We show also that the heat capacity difference between the superconducting and the normal phase is entirely determined by the order parameter. The obtained results reveal possibilities of discontinuous phase transition to the normal state and moreover, the theorem on existence of such transitions is formulated and proved. The condition for the BCS-type energy gap is given, which additionally classifies properties of the heat capacity of S-paired phase by virtue of the shape of the energy gap. In order to illustrate the developed formalism, the numerical results for the so-called statistical spin liquids and application of the established methods to the experimental data conversion, are presented and discussed.
Źródło:: Acta Physica Polonica A; 1997, 92, 6; 1177-1189
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 8.

Tytuł:: Stable States for Superconducting Systems with Combined S-Wave and D-Wave Pairing. Zero Temperature Case
Autorzy:: Kumala, W.
Gonczarek, R.
Powiązania:: https://bibliotekanauki.pl/articles/1968863.pdf
Data publikacji:: 1998-03
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
Opis:: The Fermi-liquid system with S-wave and D -wave pairing interaction harmonics is considered. The general equations for energy gap and thermodynamic potential difference for arbitrary temperatures are given. The detailed calculations are performed for zero-temperature limit. The obtained results are illustrated and discussed. The value and structure of energy gap are presented. It is showed that the anisotropic gap can be realized only for g$\text{}_{0}$ < g$\text{}_{2}$.
Źródło:: Acta Physica Polonica A; 1998, 93, 3; 539-546
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 9.

Tytuł:: Order-Disorder Mechanism and a Phenomenological Model in (Bi,Pb)-Sr-Ca-Cu-O
Autorzy:: Elboussiri, K.
Clin, M.
Rais, T.
Powiązania:: https://bibliotekanauki.pl/articles/1964220.pdf
Data publikacji:: 1997-06
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
Opis:: We established a relationship between the structures of the bismuth high T$\text{}_{c}$ superconducting compounds and a symmetry of disordered perovskite type. This description which we propose, leads to considering the structures of these materials in terms of a commensurate superstructure obtained from a latent perovskite structure of space group Im3m. A phenomenological model was elaborated in order to describe the two types of modulations realized in these compounds.
Źródło:: Acta Physica Polonica A; 1997, 91, 6; 1097-1102
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 10.

Tytuł:: Structures of Thermodynamic Functions for S-Paired Fermi Systems in Parametric Equations Approach
Autorzy:: Mulak, M.
Gonczarek, R.
Powiązania:: https://bibliotekanauki.pl/articles/1945431.pdf
Data publikacji:: 1996-05
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
Opis:: The general method of investigation of S-paired Fermi systems is given and discussed as generalization of parametric equation for the energy gap. The additional parametric equations for thermodynamic potential and heat capacity are obtained as functions of introduced parameters. The detailed calculations are given for a few exemplary chosen magnetic fields and superflows. Moreover, we consider the case of so-called statistical spin liquid, which constitutes non-BCS model.
Źródło:: Acta Physica Polonica A; 1996, 89, 5-6; 689-698
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 11.

Tytuł:: The Form and Properties of the Tight-Binding Density of States in Two Dimensions. Possible Application to Superconductivity
Autorzy:: Gładysiewicz, M.
Gonczarek, R.
Mulak, M.
Powiązania:: https://bibliotekanauki.pl/articles/2030728.pdf
Data publikacji:: 2002-06
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
74.20.Fg
Opis:: The form of the density of states for a tight-binding model with the first and the next-nearest neighbour hoppings for a rectangular planar lattice and a shift of the chemical potential are calculated. This is newly and comprehensively formulated integral form illustrated numerically, helpful in approach to two-dimensional superconducting models. In some particular cases the complete analytical forms of the density of states are obtained. It is shown that for all cases the density of states has a single van Hove singularity of the logarithmic type at the identically defined point. The proper approximate analytical representations are found. The difference between the exact numerical and approximate analytical forms is evaluated and illustrated.
Źródło:: Acta Physica Polonica A; 2002, 101, 6; 865-874
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 12.

Tytuł:: Vortex Properties in a Model with Local Pairs
Autorzy:: Śledź, Ż.
Mierzejewski, M.
Maśka, M. M.
Powiązania:: https://bibliotekanauki.pl/articles/2046800.pdf
Data publikacji:: 2006-04
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.25.Ha
74.20.-z
Opis:: We investigate the vortex structure in the Penson-Kolb model with and without impurities. We focus on the consequences arising from the non-local field-dependent pairing interaction for the vortex profile, current distribution, and the local density of states.
Źródło:: Acta Physica Polonica A; 2006, 109, 4-5; 653-656
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 13.

Tytuł:: Doped Carrier Formulation of the t-J model: Monte Carlo Study of the Anisotropic Case
Autorzy:: Ferraz, A.
Kochetov, E.
Maśka, M.
Mierzejewski, M.
Powiązania:: https://bibliotekanauki.pl/articles/1812319.pdf
Data publikacji:: 2008-07
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
74.62.Dh
Opis:: We derive a doped carrier representation of the t-J model Hamiltonian. Within this approach the t-J model is described in terms of holes hopping in a lattice of correlated spins, where holes are the carriers doped into the half-filled Mott insulator. This representation of the t-J Hamiltonian is very convenient for underdoped systems since close to half-filling it allows for a controlled treatment of the crucial constraint of no doubly occupied sites. When neglecting the transverse spin-spin interaction, the effective Hamiltonian can be investigated with classical Monte Carlo simulations. We discuss the results obtained for systems consisting of several hundred lattice sites.
Źródło:: Acta Physica Polonica A; 2008, 114, 1; 185-189
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 14.

Tytuł:: Inhomogeneous Charge Distribution and Superconductivity in the Boson-Fermion Model
Autorzy:: Śledź, Ż.
Mierzejewski, M.
Powiązania:: https://bibliotekanauki.pl/articles/1812328.pdf
Data publikacji:: 2008-07
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
74.62.Dh
Opis:: We analyze a boson-fermion model that accounts for the electrostatic potential of the out-of-plane dopant atoms. We investigate whether this approach may explain recent experimental results obtained for the Bi-based high-temperature superconductors. We demonstrate that in contradistinction to purely fermionic models, even weak electrostatic potential of the dopant atoms may be responsible for a significant modulation of the superconducting order parameter.
Źródło:: Acta Physica Polonica A; 2008, 114, 1; 219-223
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 15.

Tytuł:: Superconductivity in the Penson-Kolb Model on a Triangular Lattice
Autorzy:: Ptok, A.
Mierzejewski, M.
Powiązania:: https://bibliotekanauki.pl/articles/1812326.pdf
Data publikacji:: 2008-07
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
74.20.Rp
Opis:: We investigate properties of the two-dimensional Penson-Kolb model with repulsive pair hopping interaction. In the case of a bipartite square lattice this interaction may lead to the eta-type pairing, when the phase of superconducting order parameter changes from one lattice site to the neighboring one. We show that this interaction may be responsible for the onset of superconductivity also for a triangular lattice. We discuss the spatial dependence of the superconducting order parameter and demonstrate that the total momentum of the paired electrons is determined by the lattice geometry.
Źródło:: Acta Physica Polonica A; 2008, 114, 1; 209-212
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 16.

Tytuł:: Fermi Gas with 4-Fermion BCS-type Interaction
Autorzy:: Maćkowiak, J.
Tarasewicz, P.
Powiązania:: https://bibliotekanauki.pl/articles/1968887.pdf
Data publikacji:: 1998-04
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
74.20.Fg
Opis:: A gas of spin 1/2 fermions with an interaction V + W = - Σ$\text{}_{k,k'}$g$\text{}_{kk'}$b*$\text{}_{k}$ b*$\text{}_{-k}$b$\text{}_{k'}$b$\text{}_{-k'}$ + Σ$\text{}_{k}$ γ$\text{}_{k}$b*$\text{}_{k}$b$\text{}_{k}$, where b$\text{}_{k}$=a$\text{}_{k+}$a$\text{}_{k-}$ and a$\text{}_{kσ}$,a*$\text{}_{k'σ'}$ satisfy Fermi anticommutation relations, is investigated. The trial ground state |G〉 is similar in form to the BCS ground state, with b*$\text{}_{k}$ b*$\text{}_{-k}$ replacing a*$\text{}_{k+}$ a*$\text{}_{-k-}$, but because the excitation energies are not simply additive, the trial density matrix \rho_0 differs from the BCS one. The expectation values 〈G|H|G〉 and Tr(Hρ$\text{}_{0}$) are minimized, revealing the presence of a second-order phase transition, with T$\text{}_{c}$ > T$\text{}_{c(BCS)}$ for appropriately adjusted γ$\text{}_{k}$. It is shown that the minimization procedure applied leads to an expression for the free energy density of H, which is asymptotically exact in the infinite-volume limit. Comparison with experimental data on high-temperature superconductors is made and for a particular choice of \gamma_k qualitative agreement is found with the temperature dependence of the order parameter of the BSCCO superconductor.
Źródło:: Acta Physica Polonica A; 1998, 93, 4; 659-675
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 17.

Tytuł:: Specific Heat Study of Fulde-Ferrell-Larkin-Ovchinnikov Superconducting States in Multibands Materials - Iron-Based Systems
Autorzy:: Crivelli, D.
Ptok, A.
Powiązania:: https://bibliotekanauki.pl/articles/1398585.pdf
Data publikacji:: 2016-08
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
74.70.Xa
Opis:: The Fulde-Ferrell-Larkin-Ovchinnikov phase is the superconducting state for which the Cooper pairs have non-zero total momentum. From the time of conception of this phase, many groups have been searching for a realization of the state. Here we describe a proposal of experimental verification of this state in the case of multi-bands systems, by carrying out the specific-heat measurement.
Źródło:: Acta Physica Polonica A; 2016, 130, 2; 507-510
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 18.

Tytuł:: Hole-Doped Cuprate Panorama and the Second Neighbor Hopping
Autorzy:: Goswami, P.
Powiązania:: https://bibliotekanauki.pl/articles/1399515.pdf
Data publikacji:: 2013-07
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.72.Gh
74.20.-z
Opis:: We consider the coexistent id-density wave order, at the antiferromagnetic wave vector Q =(π,π), representing the pseudo-gap state, and d-wave superconductivity, driven by an assumed attractive interaction, within the BCS framework for the two-dimensional fermion system on a square lattice starting with a mean-field Hamiltonian involving the singlet id-density wave and the d-wave superconductivity pairings. The second-neighbor hopping, which is known to be important for cuprates and frustrates the kinetic energy of electrons, leads to the Fermi surface sheets being not connected by Q. The signature of the particle-hole asymmetry in the single-particle excitation spectrum of the pure id-density wave state is reflected in the coexisting id-density wave and d-wave superconductivity states, though the latter is characterized by the Bogoliubov quasi-particle bands - a characteristic feature of superconducting state. Quite significantly, we find that the coexistence is possible due to the non-nesting property.
Źródło:: Acta Physica Polonica A; 2013, 124, 1; 90-93
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 19.

Tytuł:: On Aharonov-Bohm Effect in Multiconnected Superconductor
Autorzy:: Sazonov, S. N.
Powiązania:: https://bibliotekanauki.pl/articles/1931826.pdf
Data publikacji:: 1994-12
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.55.+h
74.20.-z
Opis:: The system of co-axial cylinders: superconductor-ferromagnet- superconductor is considered. The temperature of the outer superconductor transition to the normal state, derived from the Ginzburg-Landau energy functional, depends on the state of the inner one. The quantity of heat is evaluated, which is liberated at the inner cylinder pushing out of core.
Źródło:: Acta Physica Polonica A; 1994, 86, 6; 987-993
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 20.

Tytuł:: Relativistic Theory of Superconductivity: BCS vs. Bogolyubov-de Gennes Approaches
Autorzy:: Ciechan, A.
Donabidowicz, A.
Wysokiński, K. I.
Powiązania:: https://bibliotekanauki.pl/articles/2041454.pdf
Data publikacji:: 2004-11
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
74.20.Fg
74.20.Rp
Opis:: In this paper we shall present the results of numerical calculations of the superconducting characteristics (temperature dependence of the gap function and specific heat) for few different symmetries of the order parameter in relativistic theory of superconductivity. We shall discuss relevance of the results to describe newly discovered superconductors, particularly those containing heavy elements with strong spin-orbit coupling.
Źródło:: Acta Physica Polonica A; 2004, 106, 5; 699-702
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 21.

Tytuł:: Modeling of Critical Current Density of Bulk High $T_c$ Superconductors
Autorzy:: Santosh, M.
Powiązania:: https://bibliotekanauki.pl/articles/1205410.pdf
Data publikacji:: 2014-08
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.72.-h
74.25.Sv
74.20.-z
Opis:: Magnetic field dependence of critical current density $(J_{c})$ of $ErBa_2Cu_3O_y$ thick film "Er-123" and melt textured $GdBa_2Cu_3O_y$ bulk "Gd-123" at liquid nitrogen temperature is reported. Gd-123 exhibits a usual peak effect at magnetic fields around 2 T, while $J_{c}$ of the Er-123 thick film continuously decreases with increasing field. The model of thermally activated flux motion was adopted to fit the critical current density of both Gd-123 and Er-123 materials. It was found that the critical current density of both types of the high $T_{c}$ materials could be modeled by the model of thermally activated flux motion utilizing a combination of two functions; one increasing and another one decreasing with field.
Źródło:: Acta Physica Polonica A; 2014, 126, 3; 808-810
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 22.

Tytuł:: Antiferromagnetism and Superconductivity in Three-Band Hubbard Model
Autorzy:: Dutka, J.
Oleś, A.
Powiązania:: https://bibliotekanauki.pl/articles/1930567.pdf
Data publikacji:: 1994-02
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 75.50.Ee
74.20.-z
Opis:: We determined the phase diagram of the three-band model for CuO$\text{}_{2}$ planes of high temperature superconductors with an attractive interoxygen interaction U$\text{}_{pp}$. The found magnetic moments of 0.47µ$\text{}_{B}$ in the undoped system, the disappearance of antiferromagnetic order at the doping of δ ≈ 0.06 hole per CuO$\text{}_{2}$ unit, as well as the enhanced tendency to superconductivity with the decreasing value of charge-transfer gap, are in good agreement with the experimental findings.
Źródło:: Acta Physica Polonica A; 1994, 85, 2; 323-327
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 23.

Tytuł:: On Realization of the Bose-Einstein Condensates and Quantum Superfluids
Autorzy:: Domański, T.
Powiązania:: https://bibliotekanauki.pl/articles/1536541.pdf
Data publikacji:: 2010-08
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
74.20.Mn
74.40.-n
Opis:: The purpose of this work is twofold. In the first part we describe superfluidity/superconductivity as an emergent phenomenon resulting from two-body correlations in presence of the Bose-Einstein condensation of particles. We briefly discuss the underlying mechanism for bosons as well as fermion pairs and illustrate various realizations of superfluidity emphasizing the recent examples. In the second part we study the glassy liquid of incoherent pairs which might exist above the transition temperature $T_{c}$ in the underdoped regime of cuprate superconductors. In particular, we explore the angular variation of pseudogap within two-dimensional version of the boson-fermion model using for a quantitative analysis the projective method. We find that above $T_{c}$ the pseudogap closes first near the nodal areas restoring there pieces (arcs) of the Fermi surface whereas remaining parts of the large Fermi surface around the antinodal points are still absent due to incoherent pairs. Upon increasing temperature the length of the Fermi arcs enlarges because the superconducting correlations are gradually suppressed. An intriguing death of Fermi surface can thus be closely related to the Bogoliubov quasiparticles whose existence in the pseudogap state has been predicted by us and confirmed recently by the angle resolved photoemission spectroscopy measurements on $Bi_2Sr_2CaCu_2O_8$ and $La_{1.895}Sr_{0.105}CuO_4$ compounds.
Źródło:: Acta Physica Polonica A; 2010, 118, 2; 204-211
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 24.

Tytuł:: Coherence Lengths for Superconductivity in the Two-Orbital Negative-U Hubbard Model
Autorzy:: Litak, G.
Örd, T.
Rägo, K.
Vargunin, A.
Powiązania:: https://bibliotekanauki.pl/articles/1431204.pdf
Data publikacji:: 2012-04
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
74.20.Mn
74.25.-q
Opis:: We study the peculiarities of coherency in the superconductivity of two-orbital system. The superconducting phase transition is caused here by the on-site intra-orbital attractions (negative-U Hubbard model) and inter-orbital pair-transfer interaction. The dependencies of critical and non-critical correlation lengths on interaction channels and band fillings are analyzed.
Źródło:: Acta Physica Polonica A; 2012, 121, 4; 747-751
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 25.

Tytuł:: On Strong Coupling Theory of Correlated Superconductors
Autorzy:: Wysokiński, K. I.
Powiązania:: https://bibliotekanauki.pl/articles/1955487.pdf
Data publikacji:: 1997-02
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
74.25.Kc
74.20.Mn
Opis:: The strong coupling or Eliashberg equations of superconductivity have been generalised to describe strongly correlated systems. Calculations show that d-wave superconductivity is stable for small hole doping. It also follows that in correlated systems one should define three different Eliashberg functions and corresponding electron- phonon coupling constants λ$\text{}_{N}$, λ$\text{}_{S}$ and λ$\text{}_{tr}$ (to describe normal (N), superconducting (S) and transport (tr) properties) each of which is measured in different kind of experiment.
Źródło:: Acta Physica Polonica A; 1997, 91, 2; 329-332
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 26.

Tytuł:: Ab Initio Lattice Dynamics of MgB$\text{}_{2}$
Autorzy:: Parlinski, K.
Powiązania:: https://bibliotekanauki.pl/articles/2028971.pdf
Data publikacji:: 2001-11
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 63.20.-e
74.20.-z
Opis:: Using the density functional theory, the phonon dispersion relations, the phonon density of states, mean square displacements, and thermodynamic functions of superconducting MgB$\text{}_{2}$ crystals have been calculated. The modes of graphite-like boron network belong to optic phonon branches, which are rather independent of the Mg vibrations.
Źródło:: Acta Physica Polonica A; 2001, 100, 5; 767-772
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 27.

Tytuł:: Destruction of Antiferromagnetic Order by Localized Polarons
Autorzy:: Wilamowski, Z.
Hankiewicz, E. M.
Powiązania:: https://bibliotekanauki.pl/articles/2013011.pdf
Data publikacji:: 2000-03
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
75.10.-b
74.20.Mn
Opis:: Analysis of a finite spin cluster indicates a possibility of the formation of purely magnetic polarons in low-dimensional antiferromagnets. It is shown that for parameters characteristic of CuO$\text{}_{2}$ based superconductors a strong antiferromagnetic polaron can occur. The destruction of antiferromagnetic order by the presence of a magnetic polaron is discussed.
Źródło:: Acta Physica Polonica A; 2000, 97, 3; 403-406
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 28.

Tytuł:: Topological Criticality on Brink of the Mott Transition in High-T$\text{}_{c}$ Superconductors
Autorzy:: Kopeć, T. K.
Powiązania:: https://bibliotekanauki.pl/articles/2046733.pdf
Data publikacji:: 2006-04
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
74.20.Fg
71.10.Pm
Opis:: The concept of topological excitations and the related ground state degeneracy are employed to establish an effective theory of the superconducting state evolving from the Mott insulator for high-T$\text{}_{c}$ cuprates. The theory includes the effects of the relevant energy scales with the emphasis on the Coulomb interaction $U$ governed by the electromagnetic U(1) compact group. The results are obtained for the layered t-t'-t$\text{}_{⊥}$-U-J system of strongly correlated electrons relevant for cuprates. Casting the Coulomb interaction in terms of composite-fermions via the gauge flux attachment facility, we show that instanton events in the Matsubara "imaginary time", labelled by a topological winding numbers, governed by gauge flux changes by an integer multiple of 2π, are essential configurations of the phase field dual to the charge. The impact of these topological excitations is calculated for the phase diagram, which displays the "hidden" quantum critical point on verge of the Mott transition that is given by a divergence of the charge compressibility.
Źródło:: Acta Physica Polonica A; 2006, 109, 4-5; 499-506
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 29.

Tytuł:: Ground State Phase Diagrams of the Extended Hubbard Model with Repulsive Pair-Hopping Interaction for Nonfrustrated 2D Lattice
Autorzy:: Czart, W.
Robaszkiewicz, S.
Powiązania:: https://bibliotekanauki.pl/articles/1385232.pdf
Data publikacji:: 2015-02
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
71.28.+d
74.20.Mn
Opis:: We analyze the extended Hubbard model with pair-hopping interaction J, i.e. the Penson-Kolb-Hubbard model, in the case of repulsive J (J < 0) within the (broken symmetry) Hartree-Fock approximation. We focus our study on the effects of on-site U interaction on the mutual stability of magnetic, charge-ordered, and superconducting states including the eta-pairing phase, i.e. the state with the Cooper-pair center-of-mass momentum q=Q. The ground state phase diagrams are obtained for arbitrary particle concentration n on nonfrustrated d=2 square lattice.
Źródło:: Acta Physica Polonica A; 2015, 127, 2; 275-277
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 30.

Tytuł:: Ground State Phase Properties of the Penson-Kolb-Hubbard Model with Attractive Pair-Hopping Interaction
Autorzy:: Czart, W.
Robaszkiewicz, S.
Powiązania:: https://bibliotekanauki.pl/articles/1385235.pdf
Data publikacji:: 2015-02
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
71.28.+d
74.20.Mn
Opis:: We study the ground state phase diagrams of the extended Hubbard model with the pair-hopping interaction J, i.e. the Penson-Kolb-Hubbard model. We concentrate on the case of attractive J (J > 0) which can stabilise s-wave pairing superconductivity in the system and competes with the on-site repulsive U. The evolution of the phase diagrams and order parameters for arbitrary electron density and representative values of the interaction parameters are analyzed within the (broken symmetry) Hartree-Fock approximation. The calculations are performed for the case of nearest-neighbors electron hopping t on the d=2 square lattice.
Źródło:: Acta Physica Polonica A; 2015, 127, 2; 278-280
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 31.

Tytuł:: Modelling of Critical Current Density of Sintered Ag Added Bulk MgB₂
Autorzy:: Santosh, M.
Powiązania:: https://bibliotekanauki.pl/articles/1398972.pdf
Data publikacji:: 2016-06
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.72.-h
74.25.Sv
74.20.-z
Opis:: Magnetic field dependence of critical current density $(J_{c})$ of bulk MgB₂ material at 20 K is reported. The selected sintered MgB₂ materials contained various amounts of silver. The silver added samples possess always a higher critical current density than the silver free ones. The critical current density increased with silver content and continuously decreased with increase of magnetic field. Further, the normalized volume pinning force density,$ f_{p}=F_{p}//F_{p,max}$, versus reduced field $h = H_{a}// H_{irr}$ for silver free and silver added samples suggested that grain boundary pinning is dominant. In essence, the model of thermal activated flux motion was successfully applied to fit the critical current density of the MgB₂ materials.
Źródło:: Acta Physica Polonica A; 2016, 129, 6; 1197-1200
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 32.

Tytuł:: Pairing Correlations around Negative-U Centre in the Two-Band Model
Autorzy:: Ciechan, A.
Wysokiński, K.
Powiązania:: https://bibliotekanauki.pl/articles/1812284.pdf
Data publikacji:: 2008-07
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
74.81.-g
74.90.+n
Opis:: The electron energy spectrum of many superconducting materials is characterised by the presence of few bands at the Fermi level. In some cases the superconducting properties seem to be dominated by single band but in others the many-band approach is essential ingredient of their description. In this paper we shall study the properties of superconducting impurity placed in a non-superconducting medium. We are interested in the evolution of superconducting correlations within non-superconducting 1- or 2-dimensional system, their dependence on the distance from impurity and changes induced by the presence of the second band and interband scattering. We use real space description of the material and Bogolyubov-de Gennes approach to superconductivity.
Źródło:: Acta Physica Polonica A; 2008, 114, 1; 123-127
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 33.

Tytuł:: The Pseudogap Phenomenon in High-T$\text{}_{c}$ Superconductors
Autorzy:: Ranninger, J.
Romano, A.
Powiązania:: https://bibliotekanauki.pl/articles/2011238.pdf
Data publikacji:: 2000-01
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
74.25.-q
74.25.Jb
Opis:: We review the possible mechanisms leading up to the phenomenon of a pseudogap which characterizes the normal-state properties of high-T$\text{}_{c}$ superconductors. We suggest that this pseudogap is not due to superconducting phase fluctuations and hence is not related to a crossover between a BCS state of Cooper pairs and a Bose-Einstein condensation of local pairs. We rather argue that it is due to uncorrelated pairing which is already manifest in the local electronic structure and accessible by photoemission and tunneling experiments.
Źródło:: Acta Physica Polonica A; 2000, 97, 1; 157-164
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 34.

Tytuł:: Superconducting Critical Temperature of Homologous Series of High-T$\text{}_{c}$ Cuprates as a Function of Number of Layers
Autorzy:: Zaleski, T. A.
Kopeć, T. K.
Powiązania:: https://bibliotekanauki.pl/articles/2038383.pdf
Data publikacji:: 2004-11
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
74.72.-h
74.50.+r
Opis:: We have considered a model of n-layer high-temperature cuprates of homologous series like HgBa$\text{}_{2}$Ca$\text{}_{n-1}$Cu$\text{}_{n}$O$\text{}_{2+2n+δ}$ to determine the dependence of the critical temperature T$\text{}_{c}$(n) on the number n of Cu-O planes in an elementary cell. Focusing on the description of the high-temperature superconducting system in terms of the collective phase variables, we have studied a semi-microscopic anisotropic three-dimensional vector XY model of stacked copper-oxide layers with adjustable parameters representing microscopic in-plane and out-of-plane phase stiffnesses. The model captures the layered composition and block structure along c-axis of superconducting homologous series. Implementing the spherical closure relation we have solved the phase XY model exactly with the help of transfer matrix method for vector variables. The calculated dependence of the critical temperature T$\text{}_{c}$(n) on the block size n is monotonic with n.
Źródło:: Acta Physica Polonica A; 2004, 106, 5; 561-567
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 35.

Tytuł:: Pseudogap and Vortices in High-Temperature Superconductors
Autorzy:: Maśka, M.
Mierzejewski, M.
Powiązania:: https://bibliotekanauki.pl/articles/2038384.pdf
Data publikacji:: 2004-11
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.25.Ha
74.25.Op
74.20.-z
Opis:: The origin of the pseudogap is one of the most puzzling features of the high-temperature superconductors. There are two main scenarios: the first one assumes the presence of a hidden order competing or coexisting with superconductivity; within the framework of the second one the pseudogap is a precursor of the superconducting gap. In this paper we present some aspects of the hidden order pseudogap scenario. In particular, we discuss how the competing order modifies the structure of vortices in high-temperature superconductors. We demonstrate that the presence of the hidden order can explain some features of vortices observed in scanning tunneling microscopy experiments.
Źródło:: Acta Physica Polonica A; 2004, 106, 5; 569-574
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 36.

Tytuł:: The Existence of the 60 K Plateau in the YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{6+y}$ Phase Diagram: the Role of Oxygen Ordering and Charge Imbalance
Autorzy:: Zaleski, T. A.
Kopeć, T. K.
Powiązania:: https://bibliotekanauki.pl/articles/2047332.pdf
Data publikacji:: 2007-05
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
74.72.Bk
74.62.-c
Opis:: We propose a semi-microscopic model of YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{6+y}$ to investigate the origin of the 60 K plateau in its phase diagram. Our model is a "phase only" approach to the high-temperature superconducting system in terms of collective variables. It is able to capture characteristic energy scales present in YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{6+y}$ by using adjustable parameters representing phase stiffnesses and allows for strong anisotropy within basal planes to simulate oxygen ordering. We solve the model calculated T$\text{}_{c}$ for chosen system parameters investigating the influence of oxygen ordering and doping imbalance on the shape of YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{6+y}$ phase diagram. Our results suggest that the oxygen ordering alone does not seem to be responsible for the existence of the 60 K plateau. However, relying on experimental data unveiling that oxygen doping of YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{6+y}$ may introduce a significant charge imbalance between CuO$\text{}_{2}$ planes and other sites, we show that simultaneously the former are underdoped, while the latter - strongly overdoped almost in the whole region of oxygen doping in which YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{6+y}$ is superconducting. This provides two natural counter acting factors, which possibly lead to rise the 60 K plateau with increasing oxygen doping.
Źródło:: Acta Physica Polonica A; 2007, 111, 5; 705-711
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 37.

Tytuł:: New Paradigm of Triplet Superconductivity
Autorzy:: Kee, H.
Morita, Y.
Maki, K.
Powiązania:: https://bibliotekanauki.pl/articles/1810293.pdf
Data publikacji:: 2009-01
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
73.43.Cd
Opis:: Since 1980, more than 10 or so triplet superconductors have been discovered. Now we can put them into two separate classes. Type A consists of e.g. $(TMTSF)_{2}PF_{6}$, $(TMTSF)_{2}ClO_{4}$, $UPt_3$, $Sr_{2}RuO_{4}$, $PrOs_{4}Sb_{12}$. These triplet superconductors are characterized with the extreme smallness of the spin-orbit coupling energy $E_{so}$ (≪ Δ, where Δ is the superconducting gap). Also like superfluid $\text{}^{3}He-A$, the order parameter of these superconductors are characterized by l^ (the chiral vector) and d^ (the spin vector). In these superconductors, an Abrikosov vortex splits into a pair of half quantum vortices at low temperatures. Type $A_{1}$ comprises most of non-centrosymmetric triplet superconductors discovered recently, e.g. $CePt_{3}Si$, $CeIrSi_3$, $CeRhSi_3$, and $Li_{2}Pt_{3}B$. They are characterized by l^ and $d_{1}^\wedge + id_{2}^\wedge $ like superfluid $\text{}^{3}He-A_{1}$. The spin-orbit coupling energy $E_{so}$ is extremely large $E_{so}≈ 10^3 K$. Therefore, as noted by Frigeri et al., the Fermi surface splits for the up-spin one and the down-spin one. However, contrary to Frigeri et al., the superconductivity should occupy only the larger Fermi surface (say for spin-up). The other Fermi surface remains in the normal state. Also in type $A_1$ superconductors, an Abrikosov vortex does not split into a pair of half quantum vortices. Further all thase triplet superconductors (both type A and type $A_1$) harbor the zero mode or the Majorana fermion attached to each vortex, of which implication should be further explored.
Źródło:: Acta Physica Polonica A; 2009, 115, 1; 73-76
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 38.

Tytuł:: Superconducting Properties of the Charged Weakly Interacting Bose Gas ("d" Symmetry)
Autorzy:: Galasiewicz, Z. M.
Powiązania:: https://bibliotekanauki.pl/articles/2014015.pdf
Data publikacji:: 2000-06
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 67.40.-w
74.20.-z
Opis:: A system of charged weakly interacting bosons with "d" symmetry is considered. The interaction U$\text{}^{(d)}$ = U$\text{}^{(s)}$ f(theta) contains the angle dependence f(theta) ~ |Y$\text{}_{2,1}$|$\text{}^{2}$ consistent with "d" symmetry. This system resembles much more free bosons than the system with "s" symmetry (interaction U$\text{}^{(s)}$). For example at T=0, n approx n$\text{}_{c}^{(d)}$, where n ≈ n$\text{}_{c}^{(d)}$ are the densities of particles and condensate respectively.
Źródło:: Acta Physica Polonica A; 2000, 97, 6; 1011-1016
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 39.

Tytuł:: Superconductivity of the Two-Dimensional Penson-Kolb Model
Autorzy:: Czart, W. R.
Robaszkiewicz, S.
Powiązania:: https://bibliotekanauki.pl/articles/2029270.pdf
Data publikacji:: 2001-12
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
71.28.+d
74.25.Ha
Opis:: Two-dimensional (d=2) Penson-Kolb model, i.e. the tight-binding model with the pair-hopping (intersite charge exchange) interaction, is considered and the effects of phase fluctuations on the s-wave superconductivity of this system are discussed within the Kosterlitz-Thouless scenario. The London penetration depth λ at T=0, the Kosterlitz-Thouless critical temperature T$\text{}_{c}$, and the Hartree-Fock approximation critical temperature T$\text{}_{p}$ are determined as a function of particle concentration and interaction. The Uemura type plots (T$\text{}_{c}$ vs.λ$\text{}^{-2}$(0)) are derived. Beyond weak coupling and for low concentrations they show the existence of universal scaling: T$\text{}_{c}$ ~1/λ$\text{}^{2}$(0), as it was previously found for the attractive Hubbard model and for the models with intersite electron pairing.
Źródło:: Acta Physica Polonica A; 2001, 100, 6; 885-895
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 40.

Tytuł:: Ground State and Thermodynamic Properties of an Induced-Pairing Model
Autorzy:: Pawłowski, G.
Robaszkiewicz, S.
Powiązania:: https://bibliotekanauki.pl/articles/1992710.pdf
Data publikacji:: 1998-10
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
71.28.+d
74.25.Ha
Opis:: We study the phase diagrams and thermodynamic properties of a system of coexisting wide-band current carriers (c-particles) and narrow-band electrons (d-electrons) which can form local pairs. There are two distinct mechanisms of superconductivity in the model considered: (i) the intersubsystem charge exchange, which leads to the superconducting state involving both types of electrons and (ii) the pair hopping interaction of d-electrons, leading to the superconducting state of d-particles only. In contrast to previous works on the subject, we assume an arbitrary value of on-site density interaction of d-electrons U, which allows us to study the effects of reduced d-pair binding energy. Within the approach in which the U term is exactly treated we determine the evolution of superconducting properties as a function of interactions and relative position of the bands. In a definite range of parameters the system shows features which are intermediate between those of a local pair superconductor and those of a classical BCS model. The increasing on-site Coulomb repulsion U competing with the intersubsystem charge exchange and the pair hopping interaction reduces the superconducting critical temperature. Moreover, it can induce a change of the superconducting transition into the first order one. Above a critical value of U, dependent on concentration of electrons and other interactions, the superconducting state cannot be stable at any temperature.
Źródło:: Acta Physica Polonica A; 1998, 94, 4; 683-699
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 41.

Tytuł:: Evolution from the BCS to the Bose-Einstein Limit in a d-Wave Superconductor at T=0
Autorzy:: Borkowski, L. S.
Sá de Melo, C. A. R.
Powiązania:: https://bibliotekanauki.pl/articles/2027398.pdf
Data publikacji:: 2001-06
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
74.25.Gz
67.40.Db
Opis:: We study the evolution from BCS to Bose limit in a two-dimensional d-wave superconductor at zero temperature and low density of charge carriers within the mean-field theory. We examine single quasiparticle properties when particle density and attraction strength are varied. For sufficiently high interaction strength there is a critical density below which the system has a gap. The spectral and thermodynamic properties of the system do not evolve smoothly from the BCS-like to the Bose-like regime.
Źródło:: Acta Physica Polonica A; 2001, 99, 6; 691-698
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 42.

Tytuł:: Spinning Superconductors and Ferromagnets
Autorzy:: Hirsch, J.
Powiązania:: https://bibliotekanauki.pl/articles/1029748.pdf
Data publikacji:: 2018-03
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
74.25.N-
75.70.Tj
Opis:: When a magnetic field is applied to a ferromagnetic body it starts to spin (Einstein-de Haas effect). This demonstrates the intimate connection between the electron's magnetic moment μ_{B}=eħ/2m_{e}c, associated with its spin angular momentum S=ħ/2, and ferromagnetism. When a magnetic field is applied to a superconducting body it also starts to spin (gyromagnetic effect), and when a normal metal in a magnetic field becomes superconducting and expels the magnetic field (Meissner effect) the body also starts to spin. Yet according to the conventional theory of superconductivity the electron's spin only role is to label states, and the electron's magnetic moment plays no role in superconductivity. Instead, within the unconventional theory of hole superconductivity, the electron's spin and associated magnetic moment play a fundamental role in superconductivity. Just like in ferromagnets the magnetization of superconductors is predicted to result from an aggregation of magnetic moments with angular momenta ħ/2. This gives rise to a "Spin Meissner effect", the existence of a spin current in the ground state of superconductors. The theory explains how a superconducting body starts spinning when it expels magnetic fields, which we argue is not explained by the conventional theory, it provides a dynamical explanation for the Meissner effect, which we argue the conventional theory cannot do, and it explains how supercurrents stop without dissipation, which we argue the conventional theory fails to explain. Essential elements of the theory of hole superconductivity are that superconductivity is driven by lowering of kinetic energy, which we have also proposed is true for ferromagnets], that the normal state charge carriers in superconducting materials are holes, and that the spin-orbit interaction plays a key role in superconductivity. The theory is proposed to apply to all superconductors.
Źródło:: Acta Physica Polonica A; 2018, 133, 3; 350-355
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 43.

Tytuł:: Coexistence of Spin-Triplet Superconductivity with Antiferromagnetism in Orbitally Degenerate System: Hartree-Fock Approximation
Autorzy:: Zegrodnik, M.
Spałek, J.
Powiązania:: https://bibliotekanauki.pl/articles/1431255.pdf
Data publikacji:: 2012-04
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
74.25.Dw
75.10.Lp
Opis:: We consider the coexistence of the Hund's-rule-exchange induced spin-triplet paired state with the antiferromagnetic ordering by starting from the extended Hubbard model for a doubly degenerate band. We use the density of states appropriate for the square lattice and treat the problem in the Hartree-Fock approximation. The temperature dependences of the superconducting gaps, the magnetic moment, and the chemical potential are presented. The free energy in the considered phase is evaluated, as well as the corresponding free energies in four additional phases: paramagnetic, ferromagnetic, superconducting of type A and superconducting of type A1 coexisting with ferromagnetism; they occur in the proper range of parameters: band filling n and the interaction parameters U/W and J/W. The low temperature values of the superconducting gaps and staggered magnetic moment are also analyzed as a function of band filling.
Źródło:: Acta Physica Polonica A; 2012, 121, 4; 801-804
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 44.

Tytuł:: Cooper Pair in Two Nonstandard Situations
Autorzy:: Wróbel, P.
Starypan, Z.
Kaczmarczyk, J.
Spałek, J.
Powiązania:: https://bibliotekanauki.pl/articles/2046740.pdf
Data publikacji:: 2006-04
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
74.25.Jb
71.10.-w
Opis:: We summarize briefly our recent work on the bound states of two electrons (Cooper pairs) in two nonstandard situations: when the quasiparticle masses depend on spin and when an electron pair is localized on a two-dimensional quantum dot and placed in an applied magnetic field. In both cases we are dealing with an extension of the original Cooper approach. The applicability of the results is briefly mentioned.
Źródło:: Acta Physica Polonica A; 2006, 109, 4-5; 541-548
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 45.

Tytuł:: Phase Diagrams of the Penson-Kolb-Hubbard Model with Repulsive Pair-Hopping Interaction
Autorzy:: Czart, W.
Robaszkiewicz, S.
Powiązania:: https://bibliotekanauki.pl/articles/1398641.pdf
Data publikacji:: 2016-08
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
71.28.+d
74.20.Mn
Opis:: We study the extended Hubbard model with on-site density-density U and intersite pair hopping J interactions, i.e. the Penson-Kolb-Hubbard model. This report focuses mainly on the properties of the model at T ≥q 0 in the case of repulsive J (J < 0) which may stabilize superconductivity with η-pairing. The analysis is performed within the (broken symmetry) Hartree-Fock approximation for arbitrary interaction parameters (J < 0 and U) and electron concentration (0 < n < 2) on the d = 2 square lattice. The phase diagrams of the model at T=0 and at finite temperatures are examined taking into account magnetic and charge-ordered phases and superconducting states with η- and s-wave pairing.
Źródło:: Acta Physica Polonica A; 2016, 130, 2; 613-616
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 46.

Tytuł:: Theoretical Approach to Strongly Correlated Systems Based on the U(1) and SU(2) Symmetry Groups
Autorzy:: Kopeć, T.
Powiązania:: https://bibliotekanauki.pl/articles/1431186.pdf
Data publikacji:: 2012-04
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
74.20.Fg
71.10.Pm
Opis:: The spin-rotationally invariant SU(2)×U(1) approach to the Hubbard model is extended to accommodate the charge degrees of freedom. Both U(1) and SU(2) gauge transformation are used to factorize the charge and spin contribution to the original electron operator in terms of the emergent gauge fields. By tracing out gauge bosons the form of paired states is established and the role of antiferromagnetic correlations is explicated. We argue that in strongly correlated electron system collective instanton excitations of the phase field (dual to the charge) arise with a great degree of stability, governed by gauge flux changes by an integer multiple of 2π. Furthermore, it is shown that U(1) and SU(2) gauge fields play a similar role as phonons in the BCS theory: they act as the the "glue" for fermion pairing.
Źródło:: Acta Physica Polonica A; 2012, 121, 4; 738-743
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 47.

Tytuł:: Temperature Dependence of the Electron Raman Light Scattering in Normal Metals and Superconductors
Autorzy:: Falkovsky, L.
Klama, S.
Powiązania:: https://bibliotekanauki.pl/articles/1930519.pdf
Data publikacji:: 1994-02
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.Fg
74.20.-z
78.30.Er
Opis:: Within the anisotropic BCS model the temperature dependence of the electron Raman light scattering in normal metals and superconductors is investigated. In either case analytical expressions describing the intensity of scattered light as a function of the Raman frequency and temperature are derived.
Źródło:: Acta Physica Polonica A; 1994, 85, 2; 311-315
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 48.

Tytuł:: "Comb-Like" Polarons and Bipolarons in High-T$\text{}_{c}$ Materials
Autorzy:: Hankiewicz, E. M.
Buczko, R.
Wilamowski, Z.
Powiązania:: https://bibliotekanauki.pl/articles/2012878.pdf
Data publikacji:: 2000-01
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
75.10.-b
74.20.Mn
Opis:: Diagonalization of Hamiltonian composed from d-d exchange interactions between localized d spins of antiferromagnetic cluster and p-d interaction with the spin of carriers indicates a possibility of formation of pure magnetic polarons. The most energetically favorable solution occurs when the carrier density in CuO$\text{}_{2}$ planes is distributed on every second spin. These "comb-like" polarons have a tendency to bind into pairs (bipolarons) "glued" by the antiferromagnetic medium.
Źródło:: Acta Physica Polonica A; 2000, 97, 1; 185-188
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 49.

Tytuł:: Theoretical Analysis of the Short Coherence Length Superconductors
Autorzy:: Wysokiński, K.
Ciechan, A.
Krzyszczak, J.
Powiązania:: https://bibliotekanauki.pl/articles/1536554.pdf
Data publikacji:: 2010-08
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 71.10.Fd
74.20.-z
74.81.-g
Opis:: Properties of the short coherence length ξ superconductors are markedly different from those with long ξ. The main difference is connected with their response to impurities. Even the s-wave superconductors have been predicted not to obey the so-called Anderson theorem and to show appreciable fluctuations of order parameter. This observation has been recently confirmed in a number of beautiful scanning tunnelling experiments on high temperature cuprate and pnictide superconductors. In this work we study clean two-band systems within BCS-type approach and impure superconductors within mean field Bogolubov-de Gennes approach. In the weak disorder limit both s-wave and d-wave superconductors only weakly react to impurities. Presence of the Van Hove singularities in the density of states of the two-band clean systems strongly increases their superconducting transition temperature if the intra-band pair scattering is the only pairing interaction. The effect of impurities on such superconductors does depend on the sign of the inter-orbital interaction.
Źródło:: Acta Physica Polonica A; 2010, 118, 2; 232-237
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 50.

Tytuł:: Inter-Orbital Effects in the Impure Pnictide Superconductors
Autorzy:: Ciechan, A.
Wysokiński, K.
Powiązania:: https://bibliotekanauki.pl/articles/1537057.pdf
Data publikacji:: 2010-08
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 71.10.Fd
74.20.-z
74.81.-g
Opis:: We study the local properties of the iron oxypnictides by means of the real space Bogolubov-de Gennes equations. Starting with the realistic energy spectrum and assuming small amount of impurities we calculate the energy dependence of the local density of states and spatial distribution of the local values of the superconducting energy gap. We pay particular attention to the role of the inter-orbital scattering of pairs and the effect of impurity scattering on the superconducting state. The effect of inter-orbital impurities depends on the relative signs of the order parameters related to two orbitals in question. For opposite signs impurities produce bound states inside the gap, while for the same sign of the order parameters they hardly affect the superconductor. The results obtained for impure systems have been shown as maps of the order parameters and local density of states. They well compare with the existing scanning tunnelling microscopy spectra of the iron pnictides.
Źródło:: Acta Physica Polonica A; 2010, 118, 2; 356-359
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 51.

Tytuł:: Inhomogeneities in Superconductors Described by the Two-Component Model
Autorzy:: Krzyszczak, J.
Domański, T.
Wysokiński, K.
Powiązania:: https://bibliotekanauki.pl/articles/1537060.pdf
Data publikacji:: 2010-08
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 71.10.Fd
74.20.-z
74.81.-g
Opis:: We study fluctuations of the superconducting order parameter of s-wave symmetry caused by nonmagnetic disorder present both in the boson and fermion subsystems using the Bogoliubov-de Gennes equations. In particular, we are interested if some features of the d-wave model persist for s-wave symmetry as well. These are: positive correlations between positions of impurities and the magnitude of energy gap, the homogeneity of the local density of states at low energies, nanoscale inhomogeneity of the coherence peak positions and their non-uniform height. We have found that spatial variations of s-wave order parameter are positively correlated with the positions of impurities. Such behavior has been observed in scanning tunneling measurements on d-wave symmetry BSCCO-2122 superconductors.
Źródło:: Acta Physica Polonica A; 2010, 118, 2; 360-363
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 52.

Tytuł:: Spin-Triplet Pairing Induced by Hunds Rule Exchange in Orbitally Degenerate Systems: Hartree-Fock Approximation
Autorzy:: Zegrodnik, M.
Spałek, J.
Powiązania:: https://bibliotekanauki.pl/articles/1426874.pdf
Data publikacji:: 2012-05
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
74.25.Dw
75.10.Lp
Opis:: We discuss the spin-triplet pairing mechanism induced by the Hund rule ferromagnetic exchange. We include explicitly the effect of interband hybridization and treat the problem by starting from an extended Hubbard model for a doubly degenerate band, making the simplest Hartree-Fock approximation for the part involving the pairing and the Hubbard interaction. The conditions of stability of various phases are determined as a function of both band filling and microscopic parameters. The phase diagram contains regions of stability of the spin-triplet superconducting phase coexisting with either saturated or non-saturated ferromagnetism. Phase diagrams for the cases of constant density of states and that of square lattice have been provided. The influence of hybridization on the stability of considered phases, as well as the temperature dependences of magnetic moment and the superconducting gap are also discussed.
Źródło:: Acta Physica Polonica A; 2012, 121, 5-6; 1051-1055
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 53.

Tytuł:: Theory of Unconventional Superconductivity in Strongly Correlated Systems: Real Space Pairing and Statistically Consistent Mean-Field Theory - in Perspective
Autorzy:: Spałek, J.
Powiązania:: https://bibliotekanauki.pl/articles/1431227.pdf
Data publikacji:: 2012-04
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 71.27.+a
74.70.Tx
74.20.-z
Opis:: In this brief overview we discuss the principal features of real space pairing as expressed via corresponding low-energy (t-J or periodic Anderson-Kondo) effective Hamiltonian, as well as consider concrete properties of those unconventional superconductors. We also rise the basic question of statistical consistency within the so-called renormalized mean-field theory. In particular, we provide the phase diagrams encompassing the stable magnetic and superconducting states. We interpret real space pairing as correlated motion of fermion pair coupled by short-range exchange interaction of magnitude J comparable to the particle renormalized band energy ≈ tx, where x is the carrier number per site. We also discuss briefly the difference between the real-space and the paramagnon-mediated sources of superconductivity. The paper concentrates both on recent novel results obtained in our research group, as well as puts the theoretical concepts in a conceptual as well as historical perspective. No slave-bosons are required to formulate the present approach.
Źródło:: Acta Physica Polonica A; 2012, 121, 4; 764-784
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 54.

Tytuł:: Real Space Bogoliubov-de Gennes Equations Study of the Boson-Fermion Model
Autorzy:: Krzyszczak, J.
Domański, T.
Wysokiński, K.
Powiązania:: https://bibliotekanauki.pl/articles/1812295.pdf
Data publikacji:: 2008-07
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 71.10.Fd
74.20.-z
74.81.-g
Opis:: The boson-fermion model was proposed to describe superconductivity in short coherence length superconductors. In this work we use it to study impurity induced inhomogeneities in high temperature superconductors as found in numerous scanning tunnelling measurements. The model was formulated in real space and solved with help of Bogoliubov-de Gennes approach. Disorder in the boson or fermion subsystem is directly coupled to the superconducting order parameter and leads to severe changes of superconducting properties like local order parameter and density of states. We present the results for many impurities randomly distributed over otherwise clean and periodic two-dimensional square lattice.
Źródło:: Acta Physica Polonica A; 2008, 114, 1; 165-169
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 55.

Tytuł:: Superfluid Characteristics of Induced-Pairing Model
Autorzy:: Czart, W. R.
Szkudlarek, M.
Robaszkiewicz, S.
Powiązania:: https://bibliotekanauki.pl/articles/1955834.pdf
Data publikacji:: 1997-02
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 71.28.+d
74.25.Ha
74.20.-z
Opis:: We study the electromagnetic and thermodynamic properties of a model of coexisting local electron pairs and itinerant carriers coupled via the intersubsystem charge exchange. The calculations of the London penetration depth, the energy gap, the magnetic critical fields and the coherence length in the superconducting phase are performed. The effects of reduced binding energy of local pairs are discussed.
Źródło:: Acta Physica Polonica A; 1997, 91, 2; 415-418
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 56.

Tytuł:: Superconducting Characteristics of the Penson-Kolb Model
Autorzy:: Czart, W. R.
Robaszkiewicz, S.
Powiązania:: https://bibliotekanauki.pl/articles/2012898.pdf
Data publikacji:: 2000-01
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
71.28.+d
74.25.Ha
Opis:: We study superconducting properties of the Penson-Kolb model, i.e. the tight-binding model with the pair-hopping (intersite charge exchange) interaction J. The evolution of the critical fields, the coherence length, the Ginzburg ratio, and the London penetration depth with particle concentration n and pairing strength are determined. The results are compared with those found earlier for the attractive Hubbard model.
Źródło:: Acta Physica Polonica A; 2000, 97, 1; 217-220
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 57.

Tytuł:: Superconducting Properties of theη-Pairing State in the Penson-Kolb-Hubbard Model
Autorzy:: Czart, W. R.
Robaszkiewicz, S.
Powiązania:: https://bibliotekanauki.pl/articles/2041460.pdf
Data publikacji:: 2004-11
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
71.28.+d
74.25.Ha
Opis:: The Penson-Kolb-Hubbard model, i.e. the Hubbard model with the pair-hopping interaction J is studied. We focus on the properties of the superconducting state with the Cooper-pair center-of-mass momentum q= Q (η-phase). The transition into theη-phase, which is favorized by the repulsive J (J<0) is found to occur only above some critical value |J$\text{}_{c}$|, dependent on band filling, on-site interaction U and band structure, and the system never exhibits standard BCS-like features. This is in obvious contrast with the properties of the isotropic s-wave state, stabilized by the attractive J and attractive U, which exhibit at T=0 a smooth crossover from the BCS-like limit to that of tightly bound pairs with increasing pairing strength.
Źródło:: Acta Physica Polonica A; 2004, 106, 5; 709-713
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 58.

Tytuł:: Remarks on the Hall Conductivity in Chiral Superconductors: Weak vs. Strong Coupling Approach
Autorzy:: Rogatko, M.
Wysokiński, K.
Powiązania:: https://bibliotekanauki.pl/articles/1374790.pdf
Data publikacji:: 2014-10
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
74.25.F-
74.70.Pq
11.25.Tq
Opis:: We discuss the calculations of the ac Hall conductivity for superconductors with the time reversal symmetry breaking states. In the weak coupling theories these states show vanishing Hall response in one band models, even though one expects otherwise on symmetry grounds. On the other hand, the strong coupling approach based on the anti-de Sitter-conformal field theory correspondence leads to the non-vanishing Hall conductivity. We discuss the possible reasons of the discrepancy. The weak coupling many orbital theory leading to the Hall conductivity with correct temperature dependence is also briefly presented.
Źródło:: Acta Physica Polonica A; 2014, 126, 4a; A-9-A-12
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 59.

Tytuł:: Influence of Coulomb Interactions on the Properties of Induced Pairing Model
Autorzy:: Czart, W. R.
Robaszkiewicz, St.
Powiązania:: https://bibliotekanauki.pl/articles/2027440.pdf
Data publikacji:: 2001-07
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
74.20.Mn
71.28.+d
74.25.Ha
Opis:: We study the superconducting properties of a model of coexisting itinerant carriers and local pairs with finite binding energy, taking into account the effects of Coulomb (density-density) and direct pair hopping interactions. The evolution of the phase diagrams and superfluid characteristics with electron concentration, interaction parameters and the relative position of the bands is examined. The model is found to exhibit several kinds of superconducting behaviors ranging from the BCS-like to the local-pair-like. The relevance of the obtained results to the interpretation of experimental data for the doped bismuthates (Ba$\text{}_{1-x}$K$\text{}_{x}$BiO$\text{}_{3}$ and BaPb$\text{}_{1-x}$BiO$\text{}_{3}$) is pointed out.
Źródło:: Acta Physica Polonica A; 2001, 100, 1; 75-88
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 60.

Tytuł:: From Weak to Strong Coupling Superconductivity: Collective Modes in a Model with Local Attraction
Autorzy:: Kostyrko, T.
Micnas, R.
Powiązania:: https://bibliotekanauki.pl/articles/1929358.pdf
Data publikacji:: 1993-06
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
71.28.+d
73.20.Mf
Opis:: We discuss the density-density response functions and the collective excitation spectrum for the extended Hubbard model with on-site attraction and arbitrary electron density, in the superconducting ground state. For the short-range intersite interaction we find the sound wave-like modes with the velocity interpolating smoothly between the weak (v ∝ 2Zt, |U| ≪ 2Zt) and strong coupling (v ∝ Zt$\text{}^{2}$/|U|,|U| ≫ 2Zt) limits. The latter agrees with the results obtained from an effective pseudospin Hamiltonian valid in the strong coupling limit. In the weak coupling regime, we obtain that apart from a commensurate charge density wave instability, an increase in the intersite Coulomb repulsion can give rise to a charge density wave incommensurate with the lattice period, away from half-filling. The ground state phase diagram for 2D square lattice, including singlet superconducting ground state, electronic droplet formation, and charge density waves is determined. It is also shown that the energy of collective excitations evolves smoothly from weak to strong coupling limit for a 2D lattice, in the case of a long-range Coulomb interaction. Finally, the mode coupling effects in the frequency behavior of the density-density response functions are analyzed.
Źródło:: Acta Physica Polonica A; 1993, 83, 6; 837-848
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 61.

Tytuł:: The Polaron Scenario for High-T$\text{}_{c}$ Superconductivity
Autorzy:: Ranninger, J.
Powiązania:: https://bibliotekanauki.pl/articles/1860957.pdf
Data publikacji:: 1994-01
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.+z
71.38.+i
67.20.+k
Opis:: On the basis of experimental evidence we conclude that high-T$\text{}_{c}$ superconducting materials are composed of two distinct subsystems: one in which electrons are bound together in form of localized pairs of small polarons (bipolarons) and one in which electrons exist as strongly correlated Fermions. Upon doping one passes at a critical doping rate from the insulating parent compounds to metallic compounds. There, a charge transfer mechanism between the two subsystems sets in abruptly by which bipolarons can decay into pairs of electrons and vice versa. Such a picture can be modelled by a mixture of interacting Bosons and Fermions. A superconducting ground state for such a system develops at low temperature which is characterized by the opening of a gap in the single electron spectrum and the appearance of collective Boson excitations with a linear spectrum which is confined to the energy regime of the gap. Above T$\text{}_{c}$, a pseudo-gap remains upon closing the superconducting gap. There are strong indications that the normal state has non Fermi liquid behaviour.
Źródło:: Acta Physica Polonica A; 1994, 85, 1; 89-102
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 62.

Tytuł:: CPA Theory of Superconducting Alloys with Diagonal and Off-Diagonal Disorder
Autorzy:: Michalik, M.
Wysokiński, K. I.
Powiązania:: https://bibliotekanauki.pl/articles/2038393.pdf
Data publikacji:: 2004-11
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 71.10.-w
71.23.-k
74.20.-z
Opis:: The general theory of disorder in superconducting alloys was discussed. We use standard Wannier function representation and allow for diagonal and off-diagonal disorder. We generalized the coherent potential approximation in the version able to deal with off-diagonal disorder in normal systems to treat superconducting state. As an illustration we calculate the quasiparticle density of states and gap function of a d-wave superconductor. We show inter alia that the rate at which superconductivity disappears depends on the kind of disorder and for off-diagonal disorder it depends on the details of its realization.
Źródło:: Acta Physica Polonica A; 2004, 106, 5; 653-658
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 63.

Tytuł:: Superconductivity versus Diagonal Disorder in the (Hard-Core) Boson-Fermion Model
Autorzy:: Pawłowski, G.
Robaszkiewicz, S.
Micnas, R.
Powiązania:: https://bibliotekanauki.pl/articles/2041476.pdf
Data publikacji:: 2004-11
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 71.45.Lr
71.55.Jv
74.20.-z
Opis:: The influence of randomness of local pair site energies on superconducting properties of a system of coexisting local pairs and itinerant electrons described by the (hard-core) boson-fermion model is analyzed within variational BCS Hartree-Fock approach. Assuming the rectangular distribution function of the random potential the phase diagrams, critical temperatures, and the chemical potential behaviours are determined.
Źródło:: Acta Physica Polonica A; 2004, 106, 5; 745-749
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 64.

Tytuł:: Off-Diagonal Long-Range Order in Many-Electron Problem
Autorzy:: Szeftel, J.
Powiązania:: https://bibliotekanauki.pl/articles/1955506.pdf
Data publikacji:: 1997-02
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 03.65.-w
74.20.-z
71.45.-d
Opis:: The interacting electron Hamiltonian H = H$\text{}_{D}$+∑$\text{}_{K,ζ}$H$\text{}_{K,ζ}$ is considered in the Hilbert space spanned by Slater determinants of Bloch wave functions. H$\text{}_{D}$ consists of the diagonal part of H in this basis. K and ζ=0, ±1 stand for the total momentum and projected spin of electron pairs and H$\text{}_{K,ζ}$ is the off-diagonal part of H describing the most general two-electron scattering process conserving K and ζ. It is shown that the eigenspectrum of H includes all eigenvalues of H$\text{}_{D}$+H$\text{}_{K,ζ}$ for every K and ζ value. The associated eigenvectors of H are shown to have off-diagonal long-range order.
Źródło:: Acta Physica Polonica A; 1997, 91, 2; 341-345
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 65.

Tytuł:: Superconducting Properties and Phase Separation Effects in Systems with Local Pairing
Autorzy:: Pawłowski, G.
Robaszkiewicz, S.
Powiązania:: https://bibliotekanauki.pl/articles/1955833.pdf
Data publikacji:: 1997-02
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 71.28.-d
74.20.-z
05.30.Jp
Opis:: We examine the phase separation effects in a class of models developed for description of superconductors with local electron pairing: (i) the extended attractive Hubbard model, (ii) the model of hard-core charged bosons on a lattice. We analyse the behaviour of various superfluid characteristics as well as the evolution of the phase diagrams with increasing external magnetic field.
Źródło:: Acta Physica Polonica A; 1997, 91, 2; 409-413
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 66.

Tytuł:: On the Anharmonic Polaronic Model
Autorzy:: Konior, J.
Powiązania:: https://bibliotekanauki.pl/articles/1923721.pdf
Data publikacji:: 1992-11
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 71.38.+i
74.20.-z
33.10.Cs
Opis:: Anharmonic polaronic model is considered. The model consists of the electronic subsystem, described within the extended Hubbard model, coupled to anharmonic local phonons. By the canonical Holstein-Lang-Firsov transformation the electron-phonon interaction term is ruled out and, then, the effective electronic Hamiltonian is obtained by averaging over the ground state of the phononic subsystem. It is shown that anharmonicity introduces two main additional factors as compared with the harmonic case. First, the band narrowing factor is less rapidly decaying function of the electron-phonon interaction strength. Second, anharmonicity introduces further renormalization of the on- and intersite interaction between fermions.
Źródło:: Acta Physica Polonica A; 1992, 82, 5; 773-776
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 67.

Tytuł:: Resonance Superfluidity in a Quantum Degenerate Fermi Gas
Autorzy:: Kokkelmans, S.
Holland, M.
Walser, R.
Chiofalo, M.
Powiązania:: https://bibliotekanauki.pl/articles/2030471.pdf
Data publikacji:: 2002-03
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 03.75.Fi
67.60.-g
74.20.-z
Opis:: We consider the superfluid phase transition that arises when a Feshbach resonance pairing occurs in a dilute Fermi gas. This is related to the phenomenon of superconductivity described by the seminal Bardeen-Cooper-Schrieffer theory. In superconductivity, the phase transition is caused by a coupling between pairs of electrons within the medium. This coupling is perturbative and leads to a critical temperature T$\text{}_{c}$ which is small compared to the Fermi temperature T$\text{}_{F}$. Even high-T$\text{}_{c}$ superconductors typically have a critical temperature which is two orders of magnitude below T$\text{}_{F}$. Here we describe a resonance pairing mechanism in a quantum degenerate gas of potassium ($\text{}^{40}$ K) atoms which leads to superfluidity in a novel regime - a regime that promises the unique opportunity to experimentally study the cross-over from the Bardeen-Cooper-Schrieffer phase of weakly-coupled fermions to the Bose-Einstein condensate of strongly-bound composite bosons. We find that the transition to a superfluid phase is possible at the high critical temperature of about 0.5 T$\text{}_{F}$. It should be straightforward to verify this prediction, since these temperatures can already be achieved experimentally.
Źródło:: Acta Physica Polonica A; 2002, 101, 3; 387-397
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 68.

Tytuł:: Unconventional Superconducting States of an Almost Localized Fermionic Liquid with Nonstandard Quasiparticles: Generalized Gutzwiller Approach
Autorzy:: Kaczmarczyk, J.
Jędrak, J.
Spałek, J.
Powiązania:: https://bibliotekanauki.pl/articles/1536614.pdf
Data publikacji:: 2010-08
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
71.27.+a
71.10.Ca
Opis:: We apply the concept of generalized (almost localized) Fermi liquid and associated with it unconventional superconductivity with Cooper pairs composed of quasiparticles with the spin dependent masses (in an applied field) and with the effective field, both induced by electron correlations. The pairing among quasiparticles takes place either in reciprocal space (Sect. 2) or in real space (Sect. 3) and is induced by the kinetic exchange of either superexchange (in the generic narrow-band situation) or Kondo-type interaction (in the Kondo-lattice limit of the periodic Anderson model). While the main features of this type of Fermi liquid have been introduced earlier, we present here a picture which is applicable to both heavy-fermion and high-$T_{c}$ superconductivity within a single narrow-band representation of correlated states. Our approach introduces a set of additional concepts (spin-dependent masses, effective fields induced by electron correlations), for which the Landau concept of the Fermi liquid represents still a workable scheme. In the limit of the Kondo lattice, we present the phase diagram incorporating the Fulde-Ferrell-Larkin-Ovchinnikov phase within the BCS-type of pairing, whereas in that of the t-J model we show that the proper choice of renormalization factors and constraints is crucial for the mean-field description of the superconducting state.
Źródło:: Acta Physica Polonica A; 2010, 118, 2; 261-266
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 69.

Tytuł:: Pseudospin Models of Superconductors with Very Short Coherence Length
Autorzy:: Robaszkiewicz, S.
Powiązania:: https://bibliotekanauki.pl/articles/1860991.pdf
Data publikacji:: 1994-01
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
05.30.Jp
71.28.+d
Opis:: We discuss a few models developed for description of superconductivity with very short coherence length and point out their formal equivalence to specific spin models, such as an anisotropic Heisenberg model (s = 1/2) with two- and four-spin exchange coupling and with fixed magnetization in the z-direction, an XY-Z model with single ion anisotropy and a Kondo-lattice model with anisotropic on-site exchange. New results concerning the phase diagram of the Hubbard model with strong attraction, the electromagnetic properties of systems with the first order superconducting transition and a possibility of local charge moment compensation in systems of coexisting bound pairs and itinerant electrons are presented.
Źródło:: Acta Physica Polonica A; 1994, 85, 1; 117-131
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 70.

Tytuł:: Coexistence of Ferromagnetism with Spin Triplet Superconductivity
Autorzy:: Górski, G.
Kucab, K.
Mizia, J.
Powiązania:: https://bibliotekanauki.pl/articles/1810408.pdf
Data publikacji:: 2009-01
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 71.10.Fd
74.20.-z
75.10.Lp
Opis:: The experimental results for $ZrZn_2$, URhGe, and in some pressure ranges also for $UGe_2$, showed that the ferromagnetic superconductors are weak itinerant ferromagnets. Guided by these results we describe the phenomenon of coexistence between equal spin triplet pairing superconductivity and ferromagnetism using the extended Stoner model, which includes in Hamiltonian the on-site Coulomb interaction, U, and occupation dependent hopping integral. We use the Hartree-Fock approximation and the Green functions technique. In the Hartree-Fock approximation the on-site Coulomb interaction plays the role of the on-site exchange (Hund's) field. All inter-site interactions will have included the inter-site kinetic correlation, 〈$c_{iσ}^{+}c_{jσ}$〉, within the Hartree-Fock approximation. We introduce the pressure-dependence to the hopping integral. Numerical results are compared with experimental data for $ZrZn_2$. The kinetic correlation creates the superconductivity without help of negative values of the Coulomb interactions. The model can explain stimulation of triplet superconductivity by the weak itinerant ferromagnetism. This effect was observed experimentally in $ZrZn_2$. Numerical analysis also confirms the experimental effect of decrease in critical temperatures (Curie and superconducting) with increasing external pressure.
Źródło:: Acta Physica Polonica A; 2009, 115, 1; 141-143
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 71.

Tytuł:: Phase Fluctuations and BCS-LP Crossover in 2D Short Coherence Length Superconductors
Autorzy:: Tobijaszewska, B.
Micnas, R.
Powiązania:: https://bibliotekanauki.pl/articles/2012966.pdf
Data publikacji:: 2000-03
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
71.10.Fd
74.20.Fg
74.20.Mn
74.72.-h
Opis:: We study the effects of phase fluctuations in 2D short-coherence length superconductors on the basis of the extended Hubbard model with intersite attraction. In the Kosterlitz-Thouless scenario the critical temperatures for anisotropic pairings were determined and compared with the ones from BCS Hartree-Fock approximation. The Uemura-type plots, i.e. the critical temperature vs. zero temperature phase stiffness, were obtained for extended s-wave and $d_{x^{2}-y^{2}}$-wave pairings. We also discuss the crossover from BCS to local pair superconductivity for d-wave pairing.
Źródło:: Acta Physica Polonica A; 2000, 97, 3; 393-397
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 72.

Tytuł:: Ground State Phase Diagram of the Extended Hubbard Model with Pair-Hopping Interaction in the Limit of Very Narrow Bandwidth
Autorzy:: Kapcia, K.
Czart, W.
Powiązania:: https://bibliotekanauki.pl/articles/1398642.pdf
Data publikacji:: 2016-08
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 71.10.Fd
71.10.Hf
74.20.-z
74.25.Dw
Opis:: The extended Hubbard model with the pair-hopping interaction, i.e. the Penson-Kolb-Hubbard model, is one of the conceptually simplest phenomenological models for studying correlations and for description of superconductivity in very narrow-band systems with short-range, almost unretarded pairing. We present ground state phase diagrams of the model derived within the broken-symmetry Hartree-Fock approximation in the narrow-bandwidth regime and compare these results with the exact ones in the atomic limit for the limit of high dimensions. The investigation of the diagrams of the model show that results obtained within both approaches are consistent, although for the case of the finite single-electron hopping phases with magnetic long-range order also occur.
Źródło:: Acta Physica Polonica A; 2016, 130, 2; 617-620
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 73.

Tytuł:: Superconductivity, Charge Density Wave and Charge Kondo States in Systems of Coexisting Itinerant Electrons and Local Pairs
Autorzy:: Sidowski, M.
Robaszkiewicz, S.
Powiązania:: https://bibliotekanauki.pl/articles/2046796.pdf
Data publikacji:: 2006-04
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.Mn
74.20.-z
75.30.Mb
71.45.Lr
Opis:: The properties of a system of coexisting local pairs and itinerant electrons described by the (hard-core) boson-fermion model are discussed. For the first time we include into analysis of the model not only the superconducting and non-ordered (normal) states but also the charge density wave phases as well as the so-called charge Kondo state. Within an extended mean-field approximation, a mutual stability of charge density wave, superconducting and charge Kondo states are determined at T = 0 in the case of half-filled fermionic and bosonic bands.
Źródło:: Acta Physica Polonica A; 2006, 109, 4-5; 647-652
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 74.

Tytuł:: Mixed State in t-U-J-V Model
Autorzy:: Tobijaszewska, B.
Bak, M.
Powiązania:: https://bibliotekanauki.pl/articles/1810406.pdf
Data publikacji:: 2009-01
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
74.20.Rp
74.25.Dw
71.10.Fd
71.27.+a
Opis:: The t-U-J-V model in the U → ∞ limit is treated by renormalized mean-field theory for arbitrary electron density. Superconductivity of s+id symmetry is found in the large parts of the phase diagram. Calculations also show a possibility of phase separation.
Źródło:: Acta Physica Polonica A; 2009, 115, 1; 135-137
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 75.

Tytuł:: Phase Separation near Half-Filling Point in Superconducting Compounds
Autorzy:: Kucab, K.
Górski, G.
Mizia, J.
Powiązania:: https://bibliotekanauki.pl/articles/1374052.pdf
Data publikacji:: 2014-10
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 71.10.Fd
74.20.-z
75.10.Lp
Opis:: We present the model of superconducting ceramics using the single band extended Hubbard Hamiltonian. We investigate the simultaneous presence of antiferromagnetism and d-wave superconductivity in the coherent potential approximation applied to the on-site Coulomb repulsion U. We consider the hopping interaction, Δt, the inter-site charge-charge interaction, V (creating superconductivity), and the single site Hund type exchange interaction, $F_\text{in}$ (creating antiferromagnetism). The influence of these interactions on the separation of superconducting and antiferromagnetic phases near the half-filling point is investigated. Results are compared with the experimental data for YBaCuO and NdCeCuO compounds.
Źródło:: Acta Physica Polonica A; 2014, 126, 4a; A-104-A-106
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 76.

Tytuł:: A Pairwise Approximation in the Hubbard Model
Autorzy:: Szeftel, J.
Powiązania:: https://bibliotekanauki.pl/articles/1930569.pdf
Data publikacji:: 1994-02
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 71.10.+x
71.45.-d
74.20.-z
Opis:: The Hubbard Hamiltonian is projected onto a representation consisting of electron pairs characterised by the momentum of their centre of mass. Within this approximation the electron gas can be viewed as a collection of subsets, each of which contains a constant number of electron pairs, all having the same centre of mass momentum. As these subsets are decoupled, the Hubbard Hamiltonian is diagonalised to give two types of many-body eigenstates: correlated and uncorrelated. The uncorrelated pairs build up an ideal Fermi gas. Excellent agreement is found for the uncorrelated energy calculated at zero temperature in one dimension between this model and the Bethe ansatz, for arbitrary electron concentration and magnitude of the electron interaction. The correlated states turn out to be of the BCS type.
Źródło:: Acta Physica Polonica A; 1994, 85, 2; 329-335
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 77.

Tytuł:: Effects of Coulomb Interactions Between Fermions on Superconductivity in Boson-Fermion Model
Autorzy:: Kostyrko, T.
Powiązania:: https://bibliotekanauki.pl/articles/1955831.pdf
Data publikacji:: 1997-02
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 67.40.Db
74.20.-z
05.30.-d
Opis:: Influence of Coulomb repulsion between fermions on stability of the superconducting state in the model of boson-like local electron pairs hybridized with wide-band fermions is studied. It is shown rigorously that the Bose condensation of the local pairs implies a divergence of the pairing susceptibility in the fermion subsystem. Charge carrier concentration dependence of the critical temperature T$\text{}_{c}$ is evaluated with the help of random phase approximation and spectral properties of the bosons at T$\text{}_{c}$ are analyzed.
Źródło:: Acta Physica Polonica A; 1997, 91, 2; 399-403
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 78.

Tytuł:: Bound States of Fermions on 2d Lattice in a Dilute Limit
Autorzy:: Bąk, M.
Micnas, R.
Powiązania:: https://bibliotekanauki.pl/articles/2012890.pdf
Data publikacji:: 2000-01
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
03.65.Ge
71.10.Fd
Opis:: We examine extended bound states in a dilute limit of the extended Hubbard model on the two-dimensional square lattice. By solving exactly the two-body problem we have determined the binding energies, mobilities, and dispersion curves across the Brillouin zone for bound states of various symmetries. It turns out that the d-wave pairing is strongly favored by the nnn hopping and the intersite local pairs can have small effective masses, even in the case of strong binding.We have also found a possibility of extended s-$d_{x^{2}-y^{2}}$ mixing of the bound states.
Źródło:: Acta Physica Polonica A; 2000, 97, 1; 209-212
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 79.

Tytuł:: Off-Diagonal Nonmagnetic Disorder in s- and d-Wave Superconductors
Autorzy:: Michalik, M.
Wysokiński, K. I.
Powiązania:: https://bibliotekanauki.pl/articles/2046788.pdf
Data publikacji:: 2006-04
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 71.10.-w
71.23.-k
74.20.-z
Opis:: The previously developed approach to study off-diagonal disorder has been extended and applied to both s- and d-wave superconductors. The derived equations allow the self-consistent solution of the problem. For a special case of negative U centres embedded in non-superconducting host we have calculated their critical concentration for the appearance of superconductivity and found it equal to≈0.4. For x>x$\text{}_{cr}$ the order parameter continuously increases to its maximal value at x=1.
Źródło:: Acta Physica Polonica A; 2006, 109, 4-5; 623-626
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 80.

Tytuł:: Superconductivity, Charge Orderings and Phase Separations in Systems with Local Electron Pairing
Autorzy:: Robaszkiewicz, S.
Pawłowski, G.
Powiązania:: https://bibliotekanauki.pl/articles/1946347.pdf
Data publikacji:: 1996-09
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
05.30.Jp
71.28.+d
Opis:: We study two effective models developed for description of superconductors with short-coherence length: (i) the extended Hubbard model with on-site attraction and intersite repulsion, (ii) the model of hard-core charged bosons on a lattice. The analysis is concentrated on the problem of phase separations and competition between superconductivity (SS) and charge-density-wave (CDW) orderings. The phase diagrams of the systems are shown to consist of at least seven different states, including 3 types of phase separated (PS) states: CDW-SS (PS1), CDW-normal (PS2) and the state of electron droplets (PS3). By taking into account the PS states and the effects of longer-range density-density interactions (beyond nearest neighbors) our paper substantially generalizes and modifies the conclusions of previous papers concerning the models considered.
Źródło:: Acta Physica Polonica A; 1996, 90, 3; 569-586
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 81.

Tytuł:: Critical Values for Electron Pairing in t-U-J-V and t-J-V Models
Autorzy:: Bak, M.
Powiązania:: https://bibliotekanauki.pl/articles/1812342.pdf
Data publikacji:: 2008-07
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
74.20.Fg
74.20.Rp
74.25.Dw
71.10.Fd
71.27.+a
Opis:: The critical values for pairing of s*- and d-wave symmetry are calculated within the t-U-J-V and the t-J-V models in renormalized mean field theory. It is shown that the first model yields the proper critical values in the low density limit while the other does not. Renormalized mean field theory strongly decreases the absolute value of (negative) critical values for larger electron densities.
Źródło:: Acta Physica Polonica A; 2008, 114, 1; 275-279
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 82.

Tytuł:: On the Ratio of the Energy Gap Amplitude to the Critical Temperature for Cuprates
Autorzy:: Szczęiśniak, R.
Durajski, A.
Powiązania:: https://bibliotekanauki.pl/articles/1382034.pdf
Data publikacji:: 2014-10
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
74.20.Fg
74.20.Mn
74.25.Bt
74.72.-h
74.72.Bk
74.72.Jt
Opis:: The model for the cuprates based on the modified electron-phonon pairing mechanism has been tested. For this purpose, the superconductors with high value of the critical temperature have been taken into consideration. In particular: $YBa_{2}Cu_{3}O_{7-y}$, $HgBa_{2}CuO_{4+y}$, $HgBa_{2}Cu_{1-x}Zn_{x}O_{4+y}$, and $HgBa_{2}Ca_{2}Cu_{3}O_{8+y}$. It has been shown that the dependence of the ratio $R_{1}$ ≡ $2Δ_\text{tot}^{(0)}$/$k_{B}T_{C}$ on the doping (p) can be properly predicted in the framework of the presented theory; the symbol $Δ_\text{tot}^{(0)}$ denotes the energy gap amplitude at the temperature of zero kelvin, and $T_{C}$ is the critical temperature. The numerical results have been supplemented by the formula which describes the function $R_{1}(p)$.
Źródło:: Acta Physica Polonica A; 2014, 126, 4a; A-92-A-96
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 83.

Tytuł:: Some Properties of the Model of a~Superconductor with Pair Hopping and Magnetic Interactions at Half-Filling
Autorzy:: Kapcia, K.
Powiązania:: https://bibliotekanauki.pl/articles/1431185.pdf
Data publikacji:: 2012-04
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 71.10.Fd
71.10.-w
74.20.-z
74.81.-g
75.30.Fv
Opis:: We present our preliminary studies of an effective model of a superconductor with short coherence length involving magnetic interactions. The Hamiltonian considered consists of (i) the effective on-site interaction U, (ii) the intersite magnetic exchange interactions ($J^z,$ $J^{xy}$) between nearest-neighbors and (iii) the intersite charge exchange term I, determining the hopping of electron pairs between nearest-neighbor sites. In the analysis of the phase diagrams and thermodynamic properties of this model for half-filling (n=1) we have adopted the variational approach, which treats the on-site interaction term exactly and the intersite interactions within the mean-field approximation. One finds that the system considered can exhibit very interesting multicritical behaviors (including tricritical, critical-end and bicritical points) caused by the competition between magnetism and superconductivity, even for n=1. Our investigations show that, depending on the values of interaction parameters, the system at half-filling can exhibit three homogeneous phases: superconducting (SS), (anti-)ferromagnetic (F) and nonordered (NO). The transitions between ordered phases (SS, F) and the NO phase can be first order as well as second order ones, whereas SS-F transition is first order one. Temperature dependencies of the order parameters and thermodynamic properties of the system at the sequence of transitions: SS→F→NO with increasing temperature for J/I=0.3, U/I_0 = 0.69 and n=1 are also presented.
Źródło:: Acta Physica Polonica A; 2012, 121, 4; 733-737
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 84.

Tytuł:: Superconductivity, Metastability and Magnetic Field Induced Phase Separation in the Atomic Limit of the Penson-Kolb-Hubbard Model
Autorzy:: Kapcia, K.
Powiązania:: https://bibliotekanauki.pl/articles/1374357.pdf
Data publikacji:: 2014-10
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 71.10.Fd
74.20.-z
64.75.Gh
71.10.Hf
74.25.Dw
Opis:: We present the analysis of paramagnetic effects of magnetic field (B) (Zeeman term) in the zero-bandwidth limit of the extended Hubbard model for arbitrary chemical potential μ and electron density n. The effective Hamiltonian considered consists of the on-site interaction U and the intersite charge exchange term I, determining the hopping of electron pairs between nearest-neighbour sites. The model has been analyzed within the variational approach, which treats the on-site interaction term exactly and the intersite interactions within the mean-field approximation (rigorous in the limit of infinite dimensions d → +∞). In this report we focus on metastable phases as well as phase separated states involving superconducting and nonordered phases and determine their ranges of occurrence for U/$I_0$=1.05 ($I_0$=zI) in the presence of magnetic field B≠0. Our investigations of the general case for arbitrary U/$I_0$ show that, depending on the values of interaction parameters (for fixed n), the phase separating state can occur in higher fields than the homogeneous superconducting phase (field-induced phase separated). Moreover, a first-order superconducting-nonordered transition occurs between metastable phases and these metastable phases can exist inside the regions of the phase separated state stability. Such behaviour is associated with the presence of tricritical line on the phase diagrams of the system.
Źródło:: Acta Physica Polonica A; 2014, 126, 4a; A-53-A-57
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 85.

Tytuł:: Electron Phase Separations Involving Superconductivity in the Extended Hubbard Models with Pair Hopping Interaction
Autorzy:: Kapcia, K.
Powiązania:: https://bibliotekanauki.pl/articles/1384819.pdf
Data publikacji:: 2015-02
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 71.10.Fd
74.20.-z
74.25.Dw
64.75.Gh
71.10.Hf
Opis:: In this work the extended Hubbard models with pair hopping interaction (at the atomic limit) are investigated within the variational approach, which treats the on-site interaction term exactly and the intersite interactions within the mean-field approximation (exact in d → +∞). We analyze mutual stability of the superconducting phase and charge or (ferro/antiferro-)magnetic orderings as well as homogeneous mixed phases. Our preliminary results for U=0 show that the superconducting phase can coexist with the charge or (ferro/antiferro-)magnetic phases only in states with electron phase separation.
Źródło:: Acta Physica Polonica A; 2015, 127, 2; 204-206
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 86.

Tytuł:: Crossover from BCS to Bose-Einstein in Hubbard Model
Autorzy:: Pedersen, M. H.
Schneider, T.
Beck, H.
Powiązania:: https://bibliotekanauki.pl/articles/1955835.pdf
Data publikacji:: 1997-02
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 71.27.+a
71.10.Fd
74.20.-z
71.10.-w
Opis:: We generalize the standard attractive Hubbard, having an on-site pair creation operator Q$\text{}_{i}$ = a$\text{}_{i↑}$a$\text{}_{i↓}$, to one with n components Q$\text{}_{iα}$ = a$\text{}_{iα↑}$a$\text{}_{iα↓}$, α=1,2,...,n. In the limit n → ∞ we obtain the Ginzburg-Landau functional. On this basis we explore the crossover from weak (BCS) to strong coupling (Bose-Einstein condensation) superconductivity. The associated self-consistent equations for the Ginzburg-Landau parameters are similar to those of the T-matrix approach. The evolution of the band structure with increasing interaction strength is studied and correlated with the behavior of the pair propagator and the transition temperature. We find that the pairing interaction creates a new band which moves downwards in energy as the interaction strength increases and separates into a lower Hubbard band when the interaction strength becomes comparable to the band width. In the strong coupling regime, a third band with small spectral weight is also found in between the lower and upper Hubbard bands.
Źródło:: Acta Physica Polonica A; 1997, 91, 2; 419-422
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 87.

Tytuł:: Phase Separations in the Narrow-Bandwidth Limit of the Penson-Kolb-Hubbard Model at Zero Temperature
Autorzy:: Kapcia, K.
Czart, W.
Powiązania:: https://bibliotekanauki.pl/articles/1030443.pdf
Data publikacji:: 2018-03
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 71.10.Fd
71.10.Hf
74.20.-z
74.25.Dw
64.75.Gh
Opis:: In this work we study the ground state of the Penson-Kolb-Hubard model in the limit of narrow-bandwidth. We present phase diagrams of the model for fixed chemical potential and concentration (involving various phase separations). The results are derived within the Hartree-Fock approximation (HFA) in the narrow-bandwidth regime and compared with the exact ones in the atomic limit and the high-dimension regime. Our investigation reveals that the HFA can reconstruct the exact diagram at the ground state when the bandwidth approaches to zero.
Źródło:: Acta Physica Polonica A; 2018, 133, 3; 401-404
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 88.

Tytuł:: Obtaining a Rough Flux Front in Type-II Superconductors Using a Critical State Model
Autorzy:: Romero-Salazar, C.
Hernández-Flores, O.
Chabanenko, V.
Kuchuk, E.
Abaloszewa, I.
Nabialek, A.
Pérez-Rodríguez, F.
Powiązania:: https://bibliotekanauki.pl/articles/1398648.pdf
Data publikacji:: 2016-08
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 74.20.-z
74.20.De
74.25.Ha
74.25.N-
74.25.Op
74.25.Sv
74.25.Wx
74.62.Dh
74.81.-g
Opis:: In this work we numerically modelled a periodic magnetic flux pattern which qualitatively reproduces the so-called sand avalanches scenario in type-II superconductors. To model these sand-pile patterns we consider a perturbation on the critical current which, as a first approximation, follows a periodic function which depends on the position.
Źródło:: Acta Physica Polonica A; 2016, 130, 2; 645-648
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 89.

Tytuł:: Electron Orderings of Half-Filled Extended Hubbard Models with Spin- and Charge-Exchange Interaction
Autorzy:: Czart, W. R.
Robaszkiewicz, S.
Powiązania:: https://bibliotekanauki.pl/articles/2046752.pdf
Data publikacji:: 2006-04
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 71.10.Fd
75.10.-b
75.30.Gw
71.45.Lr
74.20.-z
Opis:: The electron orderings of the half-filled extended Hubbard models (i) with anisotropic spin-exchange interactions (the t-U-J$\text{}_{ǁ}$-J$\text{}_{⊥}$ model) and (ii) with charge-exchange interaction (the t-U-I model) are discussed. In particular, we present new results concerning the phase diagrams of the model (i) in the case of uniaxial spin exchange (J$\text{}_{ǁ}$≢0) for d-dimensional hypercubic lattices (1≤d≤∞) and conclude about the basic effects of the particular spin- and charge-exchange interaction terms (J$\text{}_{ǁ}$, J$\text{}_{⊥}$, and I) in both models.
Źródło:: Acta Physica Polonica A; 2006, 109, 4-5; 577-582
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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