Room-temperature exciton-polaritons with two-dimensional WS2.

L C Flatten,A A P Trichet,D M Coles,R A Taylor,J H Warner,Z He,J M Smith,A W Powell

doi:10.1038/srep33134

Abstract

Two-dimensional transition metal dichalcogenides exhibit strong optical transitions with significant potential for optoelectronic devices. In particular they are suited for cavity quantum electrodynamics in which strong coupling leads to polariton formation as a root to realisation of inversionless lasing, polariton condensation and superfluidity. Demonstrations of such strongly correlated phenomena to date have often relied on cryogenic temperatures, high excitation densities and were frequently impaired by strong material disorder. At room-temperature, experiments approaching the strong coupling regime with transition metal dichalcogenides have been reported, but well resolved exciton-polaritons have yet to be achieved. Here we report a study of monolayer WS2 coupled to an open Fabry-Perot cavity at room-temperature, in which polariton eigenstates are unambiguously displayed. In-situ tunability of the cavity length results in a maximal Rabi splitting of ħΩRabi = 70 meV, exceeding the exciton linewidth. Our data are well described by a transfer matrix model appropriate for the large linewidth regime. This work provides a platform towards observing strongly correlated polariton phenomena in compact photonic devices for ambient temperature applications.

Highlights

(black, dashed) and photoluminescence spectra after off-resonant, continuous wave excitation of marked region in a. (d) Schematics of cavity setup: The left side consists of a distributed Bragg reflector (DBR) with 10 pairs of SiO2/TiO2 with single WS2 flakes transferred to the low refractive-index terminated surface
The chemical vapour deposition (CVD) grown WS2 flakes have lateral dimensions exceeding 100 μm(Fig. 1a), which are transfered with a PMMA transfer layer onto a low-index terminated distributed Bragg reflector (DBR)
The off-resonant pump leads to excitation high in the conduction band of the WS2 monolayer which is followed by a rapid thermalisation, creating an exciton bath which populates the lower polariton branch[29,30]

Summary

Introduction

(black, dashed) and photoluminescence (colour) spectra after off-resonant, continuous wave excitation (λexc = 473 nm) of marked region in a. (d) Schematics of cavity setup: The left side consists of a DBR with 10 pairs of SiO2/TiO2 with single WS2 flakes transferred to the low refractive-index terminated surface. The cavity is formed by positioning a silver mirror opposite the DBR. We extend the theoretical description of classical polariton formation to the room-temperature large linewidth regime, for which we found corrections to current theory[25]. We investigate the polariton distribution as a function of cavity detuning and coupling strength. Our findings establish a platform towards integrated polariton devices at room temperature suitable for spinoptronics and strongly correlated phenomena

Methods

Results

Conclusion