Magnetic field dependence of conductivity and effective mass of carriers in a model of Mott-Hubbard material

Abstract

The influence of external magnetic field h on a static conductivity of MottHubbard 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 σ has been calculated as a function of h, electron concentration n and temperature T . The correlated hopping is shown to cause the electron-hole asymmetry of transport properties of narrow band materials. keywordsMott-Hubbard material, conductivity, magnetic field pacs72.15-v; 72.80.Ga. The achievements of the recent years in the field of strongly correlated electron systems give us the opportunity to understand the properties of narrow-band materials, in particular those in which metal-insulator transition under the action of external influences (pressure, doping, temperature) is realized [1]. The strongly correlated electron systems demonstrate unusual transport properties [2]. For understanding of the physical mechanisms, which cause these peculiarities, the experimental and theoretical researches of the temperature dependence of conductivity are needed. The results concerning low-frequency behavior of conductivity are of the prior importance, because it gives the information about the scattering processes close to the Fermi surface. The theoretical investigation of conductivity σ(ω, T ) are mainly concentrated in the limit T = 0. Behavior of the static conductivity σ(T ) = σ(ω = 0, T ) at T > 0 has not been studied sufficiently. Theoretical investigations of the optical conductivity in the Hubbard model [3] in the frameworks of the Kubo linear response theory [4] last for many decades, we note here the investigations by analytical methods: moment method [5], in composite operators method [6], in the mean-field theory [7, 8], in the perturbative theory method [9, 10] in the limit of weak interaction (|t| ≫ U), in method of the memory function [11, 12], in the opposite limit (U ≫ |t|). The conductivity has been intensively studied in onedimensional Hubbard model [13]-[15], where the numerical results can be compared with exact ones obtained by Bethe ansatz application.