Metal–insulator transition driven by short range ferromagnetic correlations

Abstract

One of the methods used to study strongly correlated electron systems is the moment approach of Nolting, which is based on a two-pole Ansatz for the one electron Green function, G( k → ,ω) . The two energy bands and the two spectral weights are calculated via four sum rules or spectral moments. In a new hybrid approach, we use the equation of motion for G( k → ,ω) , generating G 2(i,j,ω)≡〈〈c i,σn i, σ ̄ ;c † j,σ〉〉 (ω) , hereafter also referred to as the “double occupation” Green function, which will be approximated by a one-pole Ansatz. By using an extended equation of motion we derive Nolting's solution which satisfies the first four sum rules or moments. We propose an Ansatz for the band narrowing factor, F( k → ) , which mimics ferromagnetic (FM) or antiferromagnetic (AF) correlations between nearest neighbor ions by means of a parameter J. This interaction, for J>0 (FM correlations) drives a paramagnetic metal (PM) to paramagnetic insulator (PI) transition for several values of J. We apply our proposal to pure and Cr-doped V 2O 3.