Browsing by Subject "Paramagnetism"

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    Hubbard model In Square Lattices: A Mean-field Hartree-fock Approach
    (2005) Yönaç, Muhammed
    This thesis is mainly an effort to reproduce the well-known results that HartreeFock approximation gives for the Hubbard Model in two dimensions. As the area of application magnetic phases in the finite-size square lattices was chosen. The reason of choosing this particular area is that in the sources we went through mean-field theory was used only for examining the magnetic phases for rectangular density of state not for the actual density of states of a square lattice. We used the mean-field Hartree-Fock approximation and obtained the phase diagrams for the paramagnetic, ferromagnetic, charge density wave (CDW) and spin density wave (SDW) phases. The antiferromagnetic phase was found to be a special kind of the SDW phase. The hamiltonians used for the ferromagnetic and paramagnetic cases were identical. However because of the non-diagonal correlations present in the system the CDW and SDW hamiltonian was different.
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    Spin correlations in a quasi-one-dimensional electron gas
    (Elsevier BV, 1996) Tanatar, Bilal
    We study the spin correlations in a quasi-one-dimensional electron gas within the self-consistent-field approximation (SCFA). Electrons confined in a parabolic potential restricted to have free motion in one space dimension, and interact via a Coulomb-type potential are assumed to model quantum wires as realized in semiconductor structures. Density and spin-density response of the interacting electron system is investigated where correlation effects beyond the random-phase approximation (RPA) are embodied in the local-field factors. We calculate the spin-dependent pair-correlation functions and effective potentials, and determine the paramagnon dispersion. We find that electron correlation effects signal a paramagnetic instability for rs > 1.5.