Identifying Exceptional Points in Two-Dimensional Excitons Coupled to an Open Optical Cavity

TL;DR

This paper demonstrates that polariton-like states can form in a two-dimensional exciton-cavity system without traditional strong coupling, by identifying exceptional points through experimental and theoretical analysis.

Contribution

It provides the first experimental evidence of polariton-like behavior at exceptional points without Rabi splitting in a 2D exciton-cavity system.

Findings

Observation of transition from weak to strong coupling regimes.

Identification of exceptional points in the system.

Agreement between experimental results and theoretical analysis.

Abstract

Strong coupling in the conventional sense requires that the Rabi cycling process between two interacting states is faster than other dissipation rates. Some recent experimental findings show intriguing properties that were attributed to polaritonic states (e.g., plexcitons) even though the above criterion is not satisfied. Here, we theoretically predict and provide experimental evidence of polariton-like behavior in a system that does not show Rabi splitting. The photoluminescence of an exciton-cavity system consisting of a two-dimensional exciton monolayer (tungsten disulfide, WS2) coupled to a planar, open, one-mirror optical cavity configuration is studied. We experimentally observed a transition from the weak coupling regime crossing an exceptional point to form polariton-like states by varying the coupling strength and the cavity loss. Our observations are fully in agreement with a theoretical quasi-normal mode analysis, which predicts this transition and confirms the presence of exceptional points in the system. These results provide evidence that polaritonic effects can be experimentally observed even when the conventional strong coupling condition is not satisfied.