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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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
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
Artykuł
Wyświetlanie 1-50 z 89

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