Two-dimensional Stoner transitions beyond mean-field

TL;DR

This paper investigates the nature of the two-dimensional Stoner transition beyond mean-field theory, revealing how spin and valley anisotropies influence the transition's order and susceptibility divergence, with implications for quantum well systems.

Contribution

It extends the analysis of 2D Stoner transitions beyond mean-field, highlighting the effects of valley anisotropy and density on the transition's behavior.

Findings

Suppression of the Stoner instability in low-density, isotropic systems.

Transition remains mean-field-like with larger anisotropy.

Application relevance to AlAs quantum wells.

Abstract

We have previously shown that the Stoner instability 2D has unconventional behavior: it is strongly first order but features a susceptibility which diverges at the transition point. Here, we analyze the Stoner transition for two-dimensional systems with spin and valley degrees of freedom, beyond mean field. At low density, we show that in one-valley and isotropic two-valley systems the leading effect beyond mean-field theory is suppression of the Stoner instability. In anisotropic two-valley systems, we show that, for larger anisotropy, the transition remains mean-field-like and retains its unconventional properties. We discuss applications to AlAs quantum wells.