Magnetic phases near the Van Hove singularity in s- and d-band Hubbard model

TL;DR

This paper explores how magnetic phases near the Van Hove singularity in two-dimensional Hubbard models depend on band type, electron density, and correlations, revealing differences between s- and d-band behaviors.

Contribution

It provides a comparative analysis of magnetic instabilities in s- and d-band Hubbard models considering many-body effects and local correlations.

Findings

Ferromagnetism in s-band is limited to low electron densities and flat bands.

d-band exhibits more robust ferromagnetism due to smaller reduction of the Stoner parameter.

Local spin-spin correlations have limited impact on magnetic stability.

Abstract

We investigate the magnetic instabilities of the nondegenerate (s-band) and a degenerate (d-band) Hubbard model in two dimensions using many-body effects due to the particle-particle diagrams and Hund's rule local correlations. The density of states and the position of Van Hove singularity change depending on the value of next-nearest neighbor hopping t'. The Stoner parameter is strongly reduced in the s-band case, and ferromagnetism survives only if electron density is small, and the band is almost flat at small momenta due to next-nearest neighbor hopping. In contrast, for the d-band case the reduction of the Stoner parameter which follows from particle-particle correlations is much smaller and ferromagnetism survives to a large extent. Inclusion of local spin-spin correlations has a limited destabilizing effect on the magnetic states.