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Wyświetlanie 1-15 z 89
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:
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:
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
Wyświetlanie 1-15 z 89

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