Tailoring exciton dynamics in TMDC heterobilayers in the ultranarrow gap-plasmon regime

Control of excitons in transition metal dichalcogenides (TMDCs) and their heterostructures is fundamentally interesting for tailoring light-matter interactions and exploring their potential applications in high-efficiency optoelectronic and nonlinear photonic devices. While both intra- and interlayer excitons in TMDCs have been heavily studied, their behavior in the quantum tunneling regime, in which the TMDC or its heterostructure is optically excited and concurrently serves as a tunnel junction barrier, remains unexplored. Here, using the degree of freedom of a metallic probe in an atomic force microscope, we investigated both intralayer and interlayer excitons dynamics in TMDC heterobilayers via locally controlled junction current in a finely tuned sub-nanometer tip-sample cavity. Our tip-enhanced photoluminescence measurements reveal a significantly different exciton-quantum plasmon coupling for intralayer and interlayer excitons due to different orientation of the dipoles of the respective e-h pairs. Using a steady-state rate equation fit, we extracted field gradients, radiative and nonradiative relaxation rates for excitons in the quantum tunneling regime with and without junction current. Our results show that tip-induced radiative (nonradiative) relaxation of intralayer (interlayer) excitons becomes dominant in the quantum tunneling regime due to the Purcell effect. These findings have important implications for near-field probing of excitonic materials in the strong-coupling regime.