Stoner Transition at Finite Temperature in a 2D Isotropic Fermi Liquid

TL;DR

This paper investigates the temperature-dependent behavior of the Stoner ferromagnetic transition in a 2D isotropic Fermi liquid, revealing reentrant phenomena and extending previous zero-temperature analyses.

Contribution

It introduces a finite-temperature analysis of the Stoner transition in 2D systems with flat dispersions, uncovering new reentrant behavior not observed at zero temperature.

Findings

Reentrant ferromagnetic transition at finite temperature.

Reentrant behavior increases with dispersion parameter .

Finite-temperature transition features differ from zero-temperature case.

Abstract

We present the results of a mean-field analysis of the temperature evolution of a ferromagnetic Stoner transition in a two-dimensional (2D) system with an isotropic dispersion $\varepsilon_k \propto k^{2\alpha}$, which for $\alpha >1$ models flat dispersions in various multi-layer graphene systems in a displacement field. This study is an extension to a finite $T$ of previous studies at $T=0$, which found both first-order and second-order Stoner transitions, depending on the value of $\alpha$ and special behavior at $\alpha =1$ and $\alpha =2$. We find that the Stoner transition at a finite $T$ displays new features not seen at $T=0$. The most interesting one is the reentrant behavior, where the ordered state emerges as temperature is increased. This behavior develops at $\alpha >1.4$ and the range where it holds increases with $\alpha$. We conjecture that the reentrant behavior is the fundamental feature of the Stoner transition in 2D, not sensitive to the details of the electronic structure.