Negative-mass exciton polaritons induced by dissipative light-matter coupling in an atomically thin semiconductor

TL;DR

This paper demonstrates that dissipative light-matter coupling in atomically thin semiconductors can produce exciton polaritons with negative effective mass, enabling control over their propagation and opening new avenues for quantum phases.

Contribution

It introduces a novel method of non-Hermitian dispersion engineering to create negative-mass exciton polaritons in monolayer WS$_2$ microcavities, expanding the possibilities for quantum matter.

Findings

Observation of inverted dispersion in exciton polaritons

Propagation direction opposite to momentum for negative-mass polaritons

Establishment of dissipative coupling as a tool for dispersion control

Abstract

Dispersion engineering is a powerful and versatile tool that can vary the speed of light signals and induce negative-mass effects in the dynamics of particles and quasiparticles. Here, we show that dissipative coupling between bound electron-hole pairs (excitons) and photons in an optical microcavity can lead to the formation of exciton polaritons with an inverted dispersion of the lower polariton branch and hence a negative mass. We perform direct measurements of the anomalous dispersion in atomically thin (monolayer) WS$_2$ crystals embedded in planar microcavities and demonstrate that the propagation direction of the negative-mass polaritons is opposite to their momentum. Our study introduces a new concept of non-Hermitian dispersion engineering for exciton polaritons and opens a pathway for realising new phases of quantum matter in a solid state.