Highly tunable room-temperature plexcitons in monolayer WSe2 /gap-plasmon nanocavities

TL;DR

This paper demonstrates real-time, room-temperature tunable strong plasmon-exciton coupling in monolayer WSe2 using strain and electro-mechanical control, enabling precise manipulation of plexciton states for nanophotonic applications.

Contribution

It introduces a versatile approach combining strain engineering and nano-electromechanical control to achieve tunable plexcitons in 2D materials at room temperature.

Findings

Achieved >100 meV Rabi splitting in monolayer WSe2.

Controlled exciton and plasmon resonance via pressure and voltage.

Demonstrated stable, reversible tuning over multiple cycles.

Abstract

The advancement of quantum photonic technologies relies on the ability to precisely control the degrees of freedom of optically active states. Here, we realize real-time, room-temperature tunable strong plasmon-exciton coupling in 2D semiconductor monolayers enabled by a general approach that combines strain engineering plus force- and voltage-adjustable plasmonic nanocavities. We show that the exciton energy and nanocavity plasmon resonance can be controllably toggled in concert by applying pressure with a plasmonic nanoprobe, allowing in operando control of detuning and coupling strength, with observed Rabi splittings >100 meV. Leveraging correlated force spectroscopy, nano-photoluminescence (nano-PL) and nano-Raman measurements, augmented with electromagnetic simulations, we identify distinct polariton bands and dark polariton states, and map their evolution as a function of nanogap and strain tuning. Uniquely, the system allows for manipulation of coupling strength over a range of cavity parameters without dramatically altering the detuning. Further, we establish that the tunable strong coupling is robust under multiple pressing cycles and repeated experiments over multiple nanobubbles. Finally, we show that the nanogap size can be directly modulated via an applied DC voltage between the substrate and plasmonic tip, highlighting the inherent nature of the concept as a plexcitonic nano-electro-mechanical system (NEMS). Our work demonstrates the potential to precisely control and tailor plexciton states localized in monolayer (1L) transition metal dichalcogenides (TMDs), paving the way for on-chip polariton-based nanophotonic applications spanning quantum information processing to photochemistry.