208 research outputs found
Ground state ferromagnetism in a doubly orbitally degenerate model
In the present paper the ground state of a double orbitally degenerate model
at weak intra-atomic interaction is studied using the Green functions method.
Beside the diagonal matrix elements of electron-electron interactions the model
includes correlated hopping integrals and inter-atomic exchange interaction.
The influence of orbital degeneracy with Hund's rule coupling, correlated
hopping and inter-atomic direct exchange on the ferromagnetic ordering is
investigated. The expressions for ground state energy and magnetization, the
criterion of transition from paramagnetic to ferromagnetic ground state as
functions of the model parameters are obtained. The obtained results are
compared with some experimental data for magnetic materials.Comment: 13 pages, 11 eps figure
Magnetic field dependence of conductivity and effective mass of carriers in a model of Mott-Hubbard material
The influence of external magnetic field on a static conductivity of
Mott-Hubbard material which is described by model with correlated hopping of
electrons has been investigated. By means of canonical transformation the
effective Hamiltonian which takes into account strong intra-site Coulomb
repulsion and correlated hopping is obtained. Using a variant of generalized
Hartree-Fock approximation the single-electron Green function and quasiparticle
energy spectrum of the model have been calculated. The static conductivity
has been calculated as a function of , electron concentration
and temperature . The correlated hopping is shown to cause the electron-hole
asymmetry of transport properties of narrow band materials.Comment: 10 pages, 7 figures, submitted to Condensed Matter Physics journa
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