Marginal Metals and Kosterlitz-Thouless Type Phase Transition in Disordered Altermagnets

TL;DR

This paper investigates how disorder affects two-dimensional altermagnets, revealing a Kosterlitz-Thouless type transition from a marginal metal to an insulator, with implications for experimental detection.

Contribution

It uncovers a disorder-driven phase transition in altermagnets and interprets it through vortex-antivortex pairs, advancing understanding of their stability and properties.

Findings

Discovered a disorder-induced transition from metallic to insulating phase.

Identified the transition as belonging to the Kosterlitz-Thouless class.

Showed the persistence and gradual fading of spin anisotropy across the transition.

Abstract

Altermagnetism, a recently discovered magnetic phase characterized by spin-split bands without net magnetization, has emerged as promising platform for novel physics and potential applications. However, its stability against disorder-ubiquitous in real materials-remains poorly understood. Here, we study the electron localization properties of two-dimensional $d$-wave altermagnets subject to disorder. Remarkably, we discover a disorder-driven phase transition from a marginal metallic phase to an insulator, which falls into the Kosterlitz-Thouless class. We demonstrate this by strong numerical evidence and propose an interpretation in terms of vortex-antivortex pairs in the disorder-induced local in-plane spin magnetization. Moreover, we show that the characteristic spin anisotropy of altermagnets persists but gradually fades away across the transition. These changes directly affect the spin splitting features that are detectable in angle-resolved photoemission spectroscopy and tunneling magnetoconductance. Our findings provide a new perspective on recent experimental observations of altermagnetism in candidate materials.