Current driven quantum criticality in itinerant electron ferromagnets

TL;DR

This paper investigates how an in-plane current influences the quantum critical behavior of a 2D itinerant electron ferromagnet, revealing small effects on fluctuations but potential instability in ordered states due to symmetry breaking.

Contribution

It introduces a model for nonequilibrium steady states under current flow near a quantum critical point, highlighting the effects of symmetry breaking terms on critical properties.

Findings

Current induces an effective temperature proportional to voltage drop.

Symmetry breaking terms have a small effect on critical fluctuations.

Current can destabilize classically ordered states when rotational symmetry is relevant.

Abstract

We determine the effect of an in-plane current flow on the critical properties of a 2d itinerant electron system near a ferromagnetic-paramagnetic quantum critical point. We study a model in which a nonequilibrium steady state is established as a result of exchange of particles and energy with an underlying substrate. the current $\vec{j}$ gives rise not only to an effective temperature equal to the voltage drop over a distance of order the mean free path, but also to symmetry breaking terms of the form $\vec{j}\cdot \vec{nabla}$ in the effective action. The effect of the symmetry breaking on the fluctuational and critical properties is found to be small although (in agreement with previous results) if rotational degrees of freedom are important, the current can make the classically ordered state dynamically unstable.