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

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