Magnetic switching of self-hybridized exciton-polaritons in CrSBr photonic crystal slabs

TL;DR

This study demonstrates magnetic control of exciton-polariton propagation in CrSBr photonic crystal slabs, enabling reversible switching of polariton direction with minimal magnetic field changes.

Contribution

It introduces a method to actively control polariton transport via magnetic field-induced spin-flip transitions in CrSBr photonic structures.

Findings

Polariton energy tracks magnetic phase transitions.

Reversible switching of polariton group velocity with 40 mT field.

Continuous redistribution of oscillator strength across magnetic states.

Abstract

Layered van der Waals antiferromagnet CrSBr supports strong light--matter coupling and formation of magnetically tunable exciton-polaritons, yet active magnetic control over polariton propagation direction has remained elusive. Here, we investigate self-hybridized exciton-polaritons in photonic crystal slabs fabricated from CrSBr flakes and their evolution across the antiferromagnetic-to-ferromagnetic spin-flip transition induced by moderate in-plane magnetic fields. Using angle-resolved reflectance and photoluminescence spectroscopy supported by modeling, we show that the polariton energy continuously tracks the layer-by-layer magnetization switching, revealing a gradual redistribution of oscillator strength from antiferromagnetic to ferromagnetic excitons near the critical field. Most notably, we demonstrate that the sign of the polariton group velocity can be reversed by a small change in the external magnetic field of only 40 mT, resulting in complete switching of the polariton propagation direction. Our results establish CrSBr photonic crystal slabs as a platform for magnetically controlled polariton transport, opening opportunities for active integrated photonic and polaritonic devices.