Directional Flow of Confined Polaritons in CrSBr

TL;DR

This paper demonstrates that the van der Waals magnet CrSBr inherently enables directional polariton transport and confinement due to its optical anisotropy and magneto-exciton coupling, paving the way for integrated optoelectronic devices.

Contribution

It reveals that CrSBr's intrinsic properties allow for low-loss, directional polariton guiding and confinement without complex device engineering, enhanced by microcavity embedding.

Findings

CrSBr supports low-loss guided polariton modes along the a-axis.

Strong confinement occurs along the orthogonal b-axis.

Magneto-exciton coupling enables control over propagation direction and confinement.

Abstract

Nanoscale control of energy transport is a central challenge in modern photonics. Utilization of exciton-polaritons hybrid light-matter quasiparticles is one viable approach, but it typically demands complex device engineering to enable directional transport. Here, we demonstrate that the van der Waals magnet CrSBr offers an inherent avenue for steering polariton transport leveraging a unique combination of intrinsic optical anisotropy, high refractive index, and excitons dressed by photons. This combination enables low-loss guided modes that propagate tens of microns along the crystal $a$-axis, while simultaneously inducing strong one-dimensional confinement along the orthogonal $b$-axis. By embedding CrSBr flakes in a microcavity, we further enhance the confinement, as evidenced by energy modes that are discretized along the $b$-axis but continuous along the $a$-axis. Moreover, the magneto-exciton coupling characteristic of CrSBr allows unprecedented control over both unidirectional propagation and confinement. Our results establish CrSBr as a versatile polaritonic platform for integrated optoelectronic device applications, including energy-efficient optical modulators and switches.