Exciton-Coupled Coherent Magnons in a 2D Semiconductor

TL;DR

This paper demonstrates strong coupling between excitons and coherent magnons in a 2D magnetic semiconductor, enabling optical access to spin information and long-distance magnon coherence.

Contribution

It reports the first observation of exciton-coupled coherent magnons in a 2D vdW antiferromagnetic material, with potential applications in magnonics and quantum technologies.

Findings

Magnons can coherently travel over 7 micrometers.

Coherence time of magnons exceeds 5 nanoseconds.

Coupling observed in bilayer and multilayer structures.

Abstract

Two-dimensional (2D) magnetic semiconductors feature both tightly-bound excitons with large oscillator strength and potentially long-lived coherent magnons due to the presence of bandgap and spatial confinement. While magnons and excitons are energetically mismatched by orders of magnitude, their coupling can lead to efficient optical access to spin information. Here we report strong magnon-exciton coupling in the 2D van der Waals (vdW) antiferromagnetic (AFM) semiconductor CrSBr. Coherent magnons launched by above-gap excitation modulate the interlayer hybridization, which leads to dynamic modulation of excitonic energies. Time-resolved exciton sensing reveals magnons that can coherently travel beyond 7 micrometer, with coherence time above 5 ns. We observe this exciton-coupled coherent magnons in both even and odd number of layers, with and without compensated magnetization, down to the bilayer limit. Given the versatility of vdW heterostructures, these coherent 2D magnons may be basis for optically accessible magnonics and quantum interconnects.