Anisotropic exciton-polaritons reveal non-Hermitian topology in van der Waals materials

TL;DR

This paper demonstrates topologically non-trivial exciton-polariton bands in 2D anisotropic materials within microcavities, revealing non-Hermitian phenomena like exceptional points and bulk Fermi arcs, advancing topological photonics.

Contribution

It introduces a new platform using anisotropic 2D materials to explore non-Hermitian topological physics with tunable light-matter interactions.

Findings

Observation of two pairs of exceptional points connected by bulk Fermi arcs.

Experimental band dispersion matches anisotropic Lorentz oscillator model.

Revealed non-Hermitian topology in exciton-polaritons confined in 2D materials.

Abstract

Topological band theory has expanded into various domains in applied physics, offering significant potential for future technologies. Recent developments indicate that unique bulk band topology perceived for electrons can be realized in a system of light-matter quasiparticles with reduced crystal symmetry by utilizing tunable light-matter interaction. In this work we realize topologically non-trivial energy band dispersion of exciton-polaritons confined in two-dimensional anisotropic materials inside an optical microcavity, and show the emergence of exceptional points (EPs) due to non-Hermitian topology arising from excitonic dipole oscillators with finite quasiparticle lifetime. Fourier-plane imaging reveals two pairs of EPs connected by bulk Fermi arcs for each of the transverse electric and magnetic polarized modes. An anisotropic Lorentz oscillator model captures the exact band dispersion observed in our experiment in two-dimensional momentum space. Our findings establish anisotropic two-dimensional materials as a platform for exploring non-Hermitian topological physics, with implications for polarization-controlled optical technologies.