Pseudospin-electron model spectrum in alloy analogy approximation

Stasyuk Stasyuk,Krasnov Krasnov

doi:10.5488/cmp.9.4.725

Abstract

Energy spectrum of the pseudospin-electron model is investigated in the alloy analogy approximation within the framework of the dynamical mean field theory (DMFT). The case of two near Hubbard-like electron subbands, which determine the location of chemical potential at a certain set of model parameter values, is considered. The conditions of gap appearance in the spectrum are established. The effect of the asymmetry field h and tunneling-like splitting of levels in the local anharmonic well on the critical value Ucrit of the on-site Hubbard interaction constant is investigated.

Highlights

Pseudospin-electron model (PEM) is one of the models that are used in the physics of stronglycorrelated electron systems in recent years
The electron energy spectrum of the pseudospin-electron model allowing for interaction of the near energy subbands is considered
The effective single-site problem is solved within the auxiliary fermion field approach using the procedure of different-time decoupling of the higher order Green’s functions; the alloy analogy approximation is used

Summary

Introduction

Pseudospin-electron model (PEM) is one of the models that are used in the physics of stronglycorrelated electron systems in recent years. The previous consideration of this problem in the Hubbard-I approximation [6] revealed complicated structure of the spectrum and the presence of a certain number of subbands (their appearance is caused by the correlational splitting due to Coulomb correlation U and interaction g of electrons with pseudospins). Contrary to this approach, when subbands are always energetically separated at the arbitrary U and g values, an AA approximation allows us to describe transitions with the joining of some subband and the disappearance of the gap. Based on two subbands which are close to each other at certain values of the asymmetry field h, the chemical potential of electrons being placed in the region of these subbands

Hamiltonian of the model

Dynamical mean field theory

The equations of motion for the Green’s functions

Different-time decoupling of irreducible Green’s functions

Two near subbands in alloy analogy approximation

Conclusions