Ultrafast electron dynamics in altermagnetic materials

TL;DR

This paper investigates the ultrafast spin and charge dynamics in altermagnetic materials, revealing long-lived spin polarization and contrasting behaviors with conventional magnetic materials, using a minimal tight-binding model.

Contribution

It introduces a microscopic model to study ultrafast electron dynamics in altermagnets, highlighting their unique long-lived spin polarization compared to traditional magnets.

Findings

Long-lived (~1 ps) optically excited spin polarization in altermagnets.

Contrasts with short (~10 fs) spin lifetimes in ferromagnets and antiferromagnets.

Electron-electron and electron-phonon scattering redistribute carriers in the Brillouin zone.

Abstract

Altermagnets constitute a new class of magnetic materials that combine properties previously thought to be exclusive to either antiferromagnets or ferromagnets, and have unique properties of their own. In particular, a combination of symmetries connecting magnetic sublattices gives rise to a band spin splitting exhibiting unconventional d, g, or i-wave character. Their unique electronic properties have already led to new spin-dependent transport effects. Here, we consider their spin and charge dynamics on ultrafast timescales. We use a minimal tight binding model that captures the main features of the altermagnetic candidate material KRu$_4$O$_8$. In the framework of this model, we compute the spin-dependent electronic scattering dynamics after ultrashort-pulse excitation and show through these microscopic calculations how electron-electron and electron-phonon scattering processes redistribute optically excited carriers in a 2D slice of the Brillouin zone. We find that the optically excited spin polarization is long lived (~1ps) compared to the electron-electron momentum scattering lifetime of roughly 10fs. This contrasts remarkably with the much shorter spin lifetimes observed in typical ultrafast electronic spin dynamics in conventional ferromagnets and antiferromagnets, making these pulse-driven spin excitation experiments a key probe of altermagnetism.