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    Wyświetlanie 1-4 z 4
    Tytuł:
    Chemical Potential as a Detector of Phase Transitions in Solids
    Autorzy:
    Matlak, M.
    Gosławska, E.
    Grabiec, B.
    Eid, Kh.
    Powiązania:
    https://bibliotekanauki.pl/articles/2012963.pdf
    Data publikacji:
    2000-03
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.70.-b
    75.30.Kz
    75.40.Cx
    Opis:
    We show that the chemical potential exhibits small but distinct kinks at all critical temperatures as the evidence for phase transitions in the electronic system, structural phase transitions included. In the case of, at least, two kinds of interacting electrons average occupation numbers exhibit the same behavior.
    Źródło:
    Acta Physica Polonica A; 2000, 97, 3; 365-368
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Extended Hubbard Model in the Dimer Representation. II. Lattice Hamiltonian in the Large U Limit
    Autorzy:
    Grabiec, B.
    Matlak, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/2030514.pdf
    Data publikacji:
    2002-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.10.-w
    71.10.Ca
    71.10.Fd
    Opis:
    Using the exact decomposition of the sc lattice into a set of interacting dimers (each dimer is described by the extended Hubbard Hamiltonian) and exact solution of the dimer problem (preceding paper) we exactly find the form of the extended Hubbard model in the case of a crystal in the large U limit. We apply a new, nonperturbative approach based on the exact projection procedure onto a dimer subspace occupied by electrons in this limit (it is the only assumption). The resulting Hamiltonian is very complicated and contains a variety of multiple magnetic and nonmagnetic interactions deeply hidden in its original form (site representation). We also present a simplified version of the model to better visualize a mixture of different interactions resulting from this approach.
    Źródło:
    Acta Physica Polonica A; 2002, 101, 4; 549-557
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Extended Hubbard Model in the Dimer Representation. I. Dimer Hamiltonian in the Large U Limit
    Autorzy:
    Grabiec, B.
    Matlak, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/2030513.pdf
    Data publikacji:
    2002-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.10.-w
    71.10.Ca
    71.10.Fd
    Opis:
    We consider the extended Hubbard model for the single cubic lattice and rewrite it in the form of interacting dimers, using the exact solution of the dimer problem. We analytically derive the second quantization form of the dimer Hamiltonian eliminating from the considerations unoccupied dimer energy levels in the large U limit (it is the only assumption). The resulting dimer Hamiltonian written with the use of the Hubbard operators and spin operators contains three terms, visualizing explicitly competing magnetic interactions (ferromagnetic, antiferromagnetic) as a generalization of the t-J model. The presented, nonperturbative method, can in principle be applied to the cluster of any size (e.g. one central atom and z its nearest neighbours). The use of the projection technique can further be applied in the case of a crystal to obtain the second quantization form of the extended Hubbard model for the sc lattice in the large U limit.
    Źródło:
    Acta Physica Polonica A; 2002, 101, 4; 537-548
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Electronic Correlations within Fermionic Lattice Models
    Autorzy:
    Matlak, M.
    Grabiec, B.
    Krawiec, S.
    Powiązania:
    https://bibliotekanauki.pl/articles/2047738.pdf
    Data publikacji:
    2007-09
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.10.-w
    71.10.Ca
    71.10.Fd
    71.20.Be
    71.27.+a
    71.28.+d
    73.21.La
    78.67.Bf
    Opis:
    We investigate two-site electronic correlations within generalized Hubbard model, which incorporates the conventional Hubbard model (parameters: t (hopping between nearest neighbours), U (Coulomb repulsion (attraction))) supplemented by the intersite Coulomb interactions (parameters: J$\text{}^{(1)}$ (parallel spins), J$\text{}^{(2)}$ (antiparallel spins)) and the hopping of the intrasite Cooper pairs (parameter: V). As a first step we find the eigenvalues E$\text{}_{α}$ and eigenvectors |E$\text{}_{α}$〉 of the dimer and we represent each partial Hamiltonian E$\text{}_{α}$|E $\text{}_{α}$〉〈 E$\text{}_{α}$| (α=1,2,...,16) in the second quantization with the use of the Hubbard and spin operators. Each dimer energy level possesses its own Hamiltonian describing different two-site interactions which can be active only in the case when the level will be occupied by the electrons. A typical feature is the appearance of two generalized t-J interactions ascribed to two different energy levels which do not vanish even for U=J$\text{}^{(1)}$=J{(2)}=V=0 and their coupling constants are equal to ±t in this case. In the large linebreak U-limit for J$\text{}^{(1)}$=J$\text{}^{(2)}$=V=0 there is only one t-J interaction with coupling constant equal to 4t$\text{}^{2}$/|U| as in the case of a real lattice. The competition between ferromagnetism, antiferromagnetism and superconductivity (intrasite and intersite pairings) is also a typical feature of the model because it persists in the case U=J$\text{}^{(1)}$=J$\text{}^{(2)}$=V=0 and t≢0. The same types of the electronic, competitive interactions are scattered between different energy levels and therefore their thermodynamical activities are dependent on the occupation of these levels. It qualitatively explains the origin of the phase diagram of the model. We consider also a real lattice as a set of interacting dimers to show that the competition between magnetism and superconductivity seems to be universal for fermionic lattice models.
    Źródło:
    Acta Physica Polonica A; 2007, 112, 3; 537-547
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-4 z 4

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