Phase separation of antiferromagnetic ground states in systems with imperfect nesting

TL;DR

This paper studies how imperfect nesting in electron systems leads to phase separation in antiferromagnetic ground states, revealing a broad instability due to competition between different magnetic orders.

Contribution

It demonstrates that systems with slightly mismatched Fermi surfaces are prone to electronic phase separation, expanding understanding of magnetic instabilities in such materials.

Findings

Uniform ground state is unstable to phase separation.

Instability spans a wide range of parameters.

Results applicable to chromium, pnictides, and graphene bilayers.

Abstract

We analyze the phase diagram for a system of weakly-coupled electrons having an electron- and a hole-band with imperfect nesting. Namely, both bands have spherical Fermi surfaces, but their radii are slightly different, with a mismatch proportional to the doping. Such a model is used to describe: the antiferromagnetism of chromium and its alloys, pnictides, AA-stacked graphene bilayers, as well as other systems. Here we show that the uniform ground state of this model is unstable with respect to electronic phase separation in a wide range of model parameters. Physically, this instability occurs due to the competition between commensurate and incommensurate antiferromagnetic states and could be of importance for other models with imperfect nesting.