Nanocavity Clock Spectroscopy: Resolving Competing Exciton Dynamics in WSe2/MoSe2 Heterobilayers

• DOI: 10.1021/acs.nanolett.0c03979
• Publication Date: 2020-12-11T08:52:14Z
• Authors: Molly A. May; Tao Jiang; Chenfeng Du; Kyoung-Duck Park; Xiaodong Xu; Alexey Belyanin; Markus B. Raschke
• Keywords: MOS2/WS2; WAALS; INDIRECT INTERLAYER EXCITONS; 02 engineering and technology; MONOLAYER; 530; MODE VOLUMES; near-field spectroscopy; EMITTERS; tip-enhanced photoluminescence; ULTRAFAST CHARGE-TRANSFER; HETEROSTRUCTURES; plasmonic nanocavity; EMISSION; 0210 nano-technology; exciton lifetime; TRANSITION; Interlayer exciton

Transition-metal dichalcogenide heterostructures are an emergent platform for novel many-body states from exciton condensates to nanolasers. However, their exciton dynamics are difficult to disentangle due to multiple competing processes with time scales varying over many orders of magnitude. Using a configurable nano-optical cavity based on a plasmonic scanning probe tip, the radiative (rad) and nonradiative (nrad) relaxation of intra- and interlayer excitons is controlled. Tuning their relative rates in a WSe2/MoSe2 heterobilayer over 6 orders of magnitude in tip-enhanced photoluminescence spectroscopy reveals a cavity-induced crossover from nonradiative quenching to Purcell-enhanced radiation. Rate equation modeling with the interlayer charge transfer time as a reference clock allows for a comprehensive determination from the long interlayer exciton (IX) radiative lifetime τIXrad = (94 ± 27) ns to the 5 orders of magnitude faster competing nonradiative lifetime τIXnrad = (0.6 ± 0.2) ps. This approach of nanocavity clock spectroscopy is generally applicable to a wide range of excitonic systems with competing decay pathways.