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    Wyświetlanie 1-9 z 9
    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:
    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:
    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:
    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:
    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:
    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:
    Critical Values for Electron Pairing in t-U-J-V and t-J-V Models
    Autorzy:
    Bak, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/1812342.pdf
    Data publikacji:
    2008-07
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.20.-z
    74.20.Fg
    74.20.Rp
    74.25.Dw
    71.10.Fd
    71.27.+a
    Opis:
    The critical values for pairing of s*- and d-wave symmetry are calculated within the t-U-J-V and the t-J-V models in renormalized mean field theory. It is shown that the first model yields the proper critical values in the low density limit while the other does not. Renormalized mean field theory strongly decreases the absolute value of (negative) critical values for larger electron densities.
    Źródło:
    Acta Physica Polonica A; 2008, 114, 1; 275-279
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    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
      Wyświetlanie 1-9 z 9

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