Two-particle propagator and magnetic susceptibility in the Hubbard model- An improved treatment

TL;DR

This paper introduces an improved tau-CPA method for calculating the two-particle Green's function and magnetic susceptibility in the Hubbard model, capturing spin wave spectra and magnetism with hybrid CPA and VCA techniques.

Contribution

It develops a hybrid tau-CPA approach combining CPA and VCA to better evaluate two-particle propagators and magnetic properties in the Hubbard model.

Findings

Predicts magnetism using a modified Stoner criterion.

Calculates dynamical susceptibility with vertex corrections.

Shows spin wave spectrum in ferromagnetic regime.

Abstract

We treat the two-particle Green's function in the Hubbard model using the recently developed tau-CPA, a hybrid treatment that applies the coherent-potential approximation (CPA) up to a time tau related to the inverse of the band width, after which the system is averaged using the virtual-crystal approximation (VCA). This model, with suitable approximations, does predict magnetism for a modified Stoner criterion. The evaluation of the two-particle propagator in the tau-CPA requires the solution of the pure CPA, within whose formalism the vertex correction and the weighted Green's functions are obtained. The dynamical susceptibility, including the vertex correction and the weighted scattering by the residual interaction, is calculated and shows a spin wave spectrum in the ferromagnetic regime.