Exciton transport driven by spin excitations in an antiferromagnet

TL;DR

This paper demonstrates exciton transport driven by spin excitations in the antiferromagnetic semiconductor CrSBr, revealing ultrafast, anisotropic, and superdiffusive behaviors linked to magnon currents, with implications for magneto-optical applications.

Contribution

It introduces a novel mechanism of exciton transport mediated by spin excitations in a van der Waals antiferromagnet, expanding understanding of magneto-optical interactions.

Findings

Ultrafast, nearly isotropic exciton propagation observed.

Enhanced exciton transport at the Neel temperature.

Superdiffusive behavior in bilayer samples.

Abstract

A new class of optical quasiparticles called magnetic excitons recently emerged in magnetic van der Waals materials. Akin to the highly effective strategies developed for electrons, the strong interactions of these excitons with the spin degree of freedom may provide innovative solutions for long-standing challenges in optics, such as steering the flow of energy and information. Here, we demonstrate transport of excitons by spin excitations in the van der Waals antiferromagnetic semiconductor CrSBr. Key results of our study are the observations of ultrafast, nearly isotropic exciton propagation substantially enhanced at the Neel temperature, transient contraction and expansion of the exciton clouds at low temperatures, as well as superdiffusive behavior in bilayer samples. These signatures largely defy description by commonly known exciton transport mechanisms and are related to the currents of incoherent magnons induced by laser excitation instead. We propose that the drag forces exerted by these currents can effectively imprint characteristic properties of spin excitations onto the motion of excitons. The universal nature of the underlying exciton-magnon scattering promises driving of excitons by magnons in other magnetic semiconductors and even in non-magnetic materials by proximity in heterostructures, merging the rich physics of magneto-transport with optics and photonics.