Interstitial-Electron Altermagnetism in Two Dimensions

TL;DR

This paper introduces a new mechanism for altermagnetism in two-dimensional electrides, where interstitial electrons induce magnetic order, enabling strain and ultrafast laser control of magnetic properties.

Contribution

It proposes interstitial-electron altermagnetism driven by Stoner instability, identifies candidate monolayers, and demonstrates control via strain and laser excitation.

Findings

Interstitial electrons can stabilize altermagnetic order in electrides.

Monolayers Zr2N and Ti2N are identified as candidates.

Strain and ultrafast laser excitation can control the magnetic state.

Abstract

Altermagnetism has so far been associated with compensated magnetic moments carried by atoms. Here we introduce Stoner instability induced interstitial-electron altermagnetism, a distinct mechanism in which altermagnetic order is carried instead by interstitial anionic electrons in electrides. We show that, owing to the quasi-nucleus-free nature of interstitial electrons, the Stoner instability in electrides hosting two interstitial electrons can naturally stabilize an altermagnetic state rather than the conventional ferromagnetic one. This mechanism leads to a practical design principle for two-dimensional materials, from which we identify monolayers Zr2N and Ti2N as representative candidates. The strong sensitivity of interstitial electrons to cavity size enables efficient strain control of the altermagnetic order and a pronounced piezo-altermagnetic effect. Moreover, we investigate the evolution of the magnetism in Zr2N under ultrafast laser excitation, which exhibits dynamics distinct from those in all previously reported magnetic materials where magnetism is carried by real atoms. Our work not only offers a novel pathway to realize altermagnetism but also reveals an efficient non-magnetic route for its control.