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    Wyświetlanie 1-8 z 8
    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:
    Ground State Phase Diagram of the Extended Hubbard Model with Pair-Hopping Interaction in the Limit of Very Narrow Bandwidth
    Autorzy:
    Kapcia, K.
    Czart, W.
    Powiązania:
    https://bibliotekanauki.pl/articles/1398642.pdf
    Data publikacji:
    2016-08
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.10.Fd
    71.10.Hf
    74.20.-z
    74.25.Dw
    Opis:
    The extended Hubbard model with the pair-hopping interaction, i.e. the Penson-Kolb-Hubbard model, is one of the conceptually simplest phenomenological models for studying correlations and for description of superconductivity in very narrow-band systems with short-range, almost unretarded pairing. We present ground state phase diagrams of the model derived within the broken-symmetry Hartree-Fock approximation in the narrow-bandwidth regime and compare these results with the exact ones in the atomic limit for the limit of high dimensions. The investigation of the diagrams of the model show that results obtained within both approaches are consistent, although for the case of the finite single-electron hopping phases with magnetic long-range order also occur.
    Źródło:
    Acta Physica Polonica A; 2016, 130, 2; 617-620
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    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:
    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:
    Superconductivity, Metastability and Magnetic Field Induced Phase Separation in the Atomic Limit of the Penson-Kolb-Hubbard Model
    Autorzy:
    Kapcia, K.
    Powiązania:
    https://bibliotekanauki.pl/articles/1374357.pdf
    Data publikacji:
    2014-10
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.10.Fd
    74.20.-z
    64.75.Gh
    71.10.Hf
    74.25.Dw
    Opis:
    We present the analysis of paramagnetic effects of magnetic field (B) (Zeeman term) in the zero-bandwidth limit of the extended Hubbard model for arbitrary chemical potential μ and electron density n. The effective Hamiltonian considered consists of the on-site interaction U and the intersite charge exchange term I, determining the hopping of electron pairs between nearest-neighbour sites. The model has been analyzed within the variational approach, which treats the on-site interaction term exactly and the intersite interactions within the mean-field approximation (rigorous in the limit of infinite dimensions d → +∞). In this report we focus on metastable phases as well as phase separated states involving superconducting and nonordered phases and determine their ranges of occurrence for U/$I_0$=1.05 ($I_0$=zI) in the presence of magnetic field B≠0. Our investigations of the general case for arbitrary U/$I_0$ show that, depending on the values of interaction parameters (for fixed n), the phase separating state can occur in higher fields than the homogeneous superconducting phase (field-induced phase separated). Moreover, a first-order superconducting-nonordered transition occurs between metastable phases and these metastable phases can exist inside the regions of the phase separated state stability. Such behaviour is associated with the presence of tricritical line on the phase diagrams of the system.
    Źródło:
    Acta Physica Polonica A; 2014, 126, 4a; A-53-A-57
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Electron Phase Separations Involving Superconductivity in the Extended Hubbard Models with Pair Hopping Interaction
    Autorzy:
    Kapcia, K.
    Powiązania:
    https://bibliotekanauki.pl/articles/1384819.pdf
    Data publikacji:
    2015-02
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.10.Fd
    74.20.-z
    74.25.Dw
    64.75.Gh
    71.10.Hf
    Opis:
    In this work the extended Hubbard models with pair hopping interaction (at the atomic limit) are investigated within the variational approach, which treats the on-site interaction term exactly and the intersite interactions within the mean-field approximation (exact in d → +∞). We analyze mutual stability of the superconducting phase and charge or (ferro/antiferro-)magnetic orderings as well as homogeneous mixed phases. Our preliminary results for U=0 show that the superconducting phase can coexist with the charge or (ferro/antiferro-)magnetic phases only in states with electron phase separation.
    Źródło:
    Acta Physica Polonica A; 2015, 127, 2; 204-206
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Phase Separations in the Narrow-Bandwidth Limit of the Penson-Kolb-Hubbard Model at Zero Temperature
    Autorzy:
    Kapcia, K.
    Czart, W.
    Powiązania:
    https://bibliotekanauki.pl/articles/1030443.pdf
    Data publikacji:
    2018-03
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.10.Fd
    71.10.Hf
    74.20.-z
    74.25.Dw
    64.75.Gh
    Opis:
    In this work we study the ground state of the Penson-Kolb-Hubard model in the limit of narrow-bandwidth. We present phase diagrams of the model for fixed chemical potential and concentration (involving various phase separations). The results are derived within the Hartree-Fock approximation (HFA) in the narrow-bandwidth regime and compared with the exact ones in the atomic limit and the high-dimension regime. Our investigation reveals that the HFA can reconstruct the exact diagram at the ground state when the bandwidth approaches to zero.
    Źródło:
    Acta Physica Polonica A; 2018, 133, 3; 401-404
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-8 z 8

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