Electron-hole asymmetry in electron systems with orbital degeneracy and correlated hopping

Skorenkyy Skorenkyy,Kramar Kramar,Dovhopyaty Dovhopyaty

doi:10.5488/cmp.23.43714

Abstract

Microscopic models of electronic subsystems with orbital degeneracy of energy states and non-diagonal matrix elements of electron interactions (correlated hopping) are considered within the configuration-operator approach. Equations for arbitrary-temperature numerical calculation of the doublon concentration for the integer band filling $n=1$ at different forms of the model density of states are derived. The energy spectra obtained within the Green function method are discussed with special emphasis on the role of correlated hopping in transition from itinerant to localized behavior observed in vanadium Magneli phases V$_n$O$_{2n-1}$, transition-metal dichalcogenides NiS$_{2-x}$Se$_x$, fulleride A$_n$C$_{60}$ systems.

Highlights

The idea of interaction-driven electron localization in a paramagnet due to Coulomb forces and attempts to explain ferromagnetism of transition metals have led to the elaboration of extremely simple and insightful models of quantum statistics, namely Anderson model [3] and Hubbard model [4]
To describe the peculiarities of real materials, the matrix elements of electron interactions neglected in the original form of the Hubbard model as well as orbital degeneracy of atomic energy levels [10, 11] are to be taken into account
Continuing the studies of non-denenerate Hubbard model generalized with taking into account the correlated hopping of electrons, quasiparticle energy spectra for doubly- and triply degenerated model are calculated to show that both the orbital degeneracy and the correlated hopping remove the particle-hole symmetry and have a strong effect on the electron localization

Summary

Introduction

The idea of interaction-driven electron localization in a paramagnet due to Coulomb forces (the Mott transition [1, 2]) and attempts to explain ferromagnetism of transition metals have led to the elaboration of extremely simple and insightful models of quantum statistics, namely Anderson model [3] and Hubbard model [4]. To describe the peculiarities of real materials, the matrix elements of electron interactions neglected in the original form of the Hubbard model as well as orbital degeneracy of atomic energy levels [10, 11] are to be taken into account. The present study is devoted to investigation of a system close to Mott-Hubbard transition within the models taking into account the orbital degeneracy of energy levels, strong Coulomb interaction and correlated hopping of electrons. Where niσ = ai+σaiσ is the site occupancy operator, hopping integrals tij(n), Tij taking into account two types of correlated hopping of electrons [37] in non-degenerate model are introduced Such a generalized model is not invariant under particle-hole transformation ai+σ → aiσ, in distinction from the Hubbard model [45]

Hdeg Hloc Htr

Results and discussion

In analogous way we obtain equation with C

Conclusions