Brightening of a dark monolayer semiconductor via strong light-matter coupling in a cavity

Abstract

Engineering the properties of quantum materials via strong light-matter coupling is a compelling research direction with a multiplicity of modern applications. Those range from modifying charge transport in organic molecules, steering particle correlation and interactions, and even controlling chemical reactions. Here, we study the modification of the material properties via strong coupling and demonstrate an effective inversion of the excitonic band-ordering in a monolayer of WSe2 with spin-forbidden, optically dark ground state. In our experiments, we harness the strong light-matter coupling between cavity photon and the high energy, spin-allowed bright exciton, and thus creating two bright polaritonic modes in the optical bandgap with the lower polariton mode pushed below the WSe2 dark state. We demonstrate that in this regime the commonly observed luminescence quenching stemming from the fast relaxation to the dark ground state is prevented, which results in the brightening of this intrinsically dark material. We probe this effective brightening by temperature-dependent photoluminescence, and we find an excellent agreement with a theoretical model accounting for the inversion of the band ordering and phonon-assisted polariton relaxation.

Room‐Temperature Exceptional‐Point‐Driven Polariton Lasing from Perovskite Metasurface

“…As a result, there exists a balance between these two effects on the polariton branch, where polaritons may efficiently accumulate and cause polariton stimulation in this state after some threshold. [24,25]…”

“…The reason for the observed effect is supposed to be in the origin of the polariton relaxation. [25,27] In the case of the ASE, the accumulated polaritons in a nonlinear regime scatter to the lower energies, as there does not exist a state where a large number of polaritons can be accumulated. However, in the lasing sample, in a nonlinear regime, there appear the specific states at the k x /k 0 ≈ 0, where the polariton condensation with a narrow lasing emission is achieved.…”

“…[ 22,23 ] If EPs appear on a polariton branch, this causes a strong enhancement of the boson scattering probability to this state, which can lead to the polariton accumulation in a nonlinear regime, resulting in the polariton lasing. [ 24,25 ]…”

“…[22,23] If EPs appear on a polariton branch, this causes a strong enhancement of the boson scattering probability to this state, which can lead to the polariton accumulation in a nonlinear regime, resulting in the polariton lasing. [24,25] In turn, halide perovskites are one of the most promising candidates to be an active medium for the metasurface-based polariton lasers. This group of materials was proved to be a promising photo-active material for photovoltaics and optoelectronics.…”

Giant Ultrafast All-Optical Modulation Based on Exceptional Points in Exciton–Polariton Perovskite Metasurfaces

“…49 In turn, the reduction of τ mod is attributed to the fact that stimulated polariton relaxation is a nonlinear process, with its rate scaling proportionally to the square of the polariton concentration. 60,61 This nonlinear scaling results in an accelerated stimulated polariton relaxation rate to the condensed state and, consequently, a reduction in the modulation time with an increasing pump fluence, as shown in Figure 3d. At the point of maximum transmission modulation, τ mod is observed to be equal to 440 fs.…”