Motional narrowing, ballistic transport, and trapping of room-temperature exciton polaritons in an atomically-thin semiconductor

M Wurdack,T Yun,A G Truscott,E Estrecho,S K Earl,S Todd,E A Ostrovskaya,C Schneider,M Pieczarka,J A Davis

doi:10.1038/s41467-021-25656-7

Abstract

Monolayer transition metal dichalcogenide crystals (TMDCs) hold great promise for semiconductor optoelectronics because their bound electron-hole pairs (excitons) are stable at room temperature and interact strongly with light. When TMDCs are embedded in an optical microcavity, excitons can hybridise with cavity photons to form exciton polaritons, which inherit useful properties from their constituents. The ability to manipulate and trap polaritons on a microchip is critical for applications. Here, we create a non-trivial potential landscape for polaritons in monolayer WS2, and demonstrate their trapping and ballistic propagation across tens of micrometers. We show that the effects of dielectric disorder, which restrict the diffusion of WS2 excitons and broaden their spectral resonance, are dramatically reduced for polaritons, leading to motional narrowing and preserved partial coherence. Linewidth narrowing and coherence are further enhanced in the trap. Our results demonstrate the possibility of long-range dissipationless transport and efficient trapping of TMDC polaritons in ambient conditions.

Highlights

Monolayer transition metal dichalcogenide crystals (TMDCs) hold great promise for semiconductor optoelectronics because their bound electron-hole pairs are stable at room temperature and interact strongly with light
The all-dielectric monolithic microcavity investigated in this work was fabricated with the flip-chip approach[26,35], by transferring a small piece of a dielectric Bragg reflector (DBR) from a polypropylene carbonate (PPC) film onto a DBR substrate at the position of a mechanically exfoliated WS2 monolayer
Measuring the polariton emission spectrum along the dashed line at the angle of approximately zero incidence allows us to estimate the profile of the potential landscape[34,39] for polaritons corresponding to zero kinetic energy. This measurement reveals the non-trivial shape of the potential caused by strong variation of the detuning between the cavity photon energy, EC, and the exciton resonance, EX. This variation is likely caused by an air gap between the DBR chip and the DBR substrate, which leads to a local modification of the cavity length

Summary

Introduction

Monolayer transition metal dichalcogenide crystals (TMDCs) hold great promise for semiconductor optoelectronics because their bound electron-hole pairs (excitons) are stable at room temperature and interact strongly with light. Polariton condensation and trapping in engineered potential landscapes at room temperature were demonstrated by utilising semiconductors with large exciton binding energies[12,13,14,15,16,17,18,19,20,21], the search for the optimal polaritonic material platforms that combine stability of the samples and low disorder continues[8]. We demonstrate room-temperature WS2 polaritons under non-resonant continuous-wave (cw) optical excitation in a high-quality all-dielectric monolithic microcavity with a nontrivial potential landscape This potential landscape allows us to investigate both free and trapped WS2 polaritons in the “thermal” regime, below the onset of bosonic condensation. Long-range transport of polaritons enables their trapping in a quasi-1D potential well, even when the excitation spot is located tens of micrometers away from the trap

Methods

Results

Conclusion