Magnetizing altermagnets by ultrafast asymmetric spin dynamics

TL;DR

This paper demonstrates that linearly polarized ultrafast laser pulses can induce a controllable net magnetization in altermagnets by asymmetric spin dynamics, revealing a universal, light-controlled magnetization mechanism.

Contribution

The study introduces a novel method to generate and control magnetization in altermagnets using ultrafast laser pulses, highlighting the role of polarization and spin transfer mechanisms.

Findings

Laser pulses induce a photo-magnetized state in altermagnets.

Magnetization controllable by laser polarization.

Universal applicability across various d-wave altermagnets.

Abstract

Laser pulses are known to induce symmetric demagnetization: equal loss of magnetic moments in the identical sublattices of antiferromagnets and ferromagnets at ultrashort timescales. Using time-dependent density functional theory, we show that linearly polarized laser pulses can drive asymmetric demagnetization between otherwise identical sublattices in the $d$-wave compensated altermagnet (AM) RuO$_2$, resulting in a \textit{photo-induced ferrimagnetic state} with a strong net magnetization of $\sim$0.2 $\mu_B$ per unit cell. The sign and magnitude of this metastable magnetization are highly controllable by laser polarization. We identify polarization-selective asymmetric optical intersite spin transfer (a-OISTR) as the primary mechanism generating the net moment, followed by asymmetric spin flips (a-SF) that further amplifies it. Both effects originate from the characteristic nodal spin band topology of \textit{d}-wave AMs. Moreover, we demonstrate that this laser-induced magnetization is universal across various $d$-wave AMs, including experimentally confirmed KV$_2$Se$_2$O and RbV$_2$Te$_2$O. We uncover a robust route to light-controlled magnetization in AMs on ultrafast timescales.