Probing dark exciton navigation through a local strain landscape in a WSe 2 monolayer

• Published in: Nature communications Vol. 13; no. 1; p. 232
• Main Authors: Gelly, Ryan J, Renaud, Dylan, Liao, Xing, Pingault, Benjamin, Bogdanovic, Stefan, Scuri, Giovanni, Watanabe, Kenji, Taniguchi, Takashi, Urbaszek, Bernhard, Park, Hongkun, Lončar, Marko
• Format: Journal Article
• Language: English
• Published: England 11.01.2022
• ISSN: 2041-1723

In WSe monolayers, strain has been used to control the energy of excitons, induce funneling, and realize single-photon sources. Here, we developed a technique for probing the dynamics of free excitons in nanoscale strain landscapes in such monolayers. A nanosculpted tapered optical fiber is used to simultaneously generate strain and probe the near-field optical response of WSe monolayers at 5 K. When the monolayer is pushed by the fiber, its lowest energy states shift by as much as 390 meV (>20% of the bandgap of a WSe monolayer). Polarization and lifetime measurements of these red-shifting peaks indicate they originate from dark excitons. We conclude free dark excitons are funneled to high-strain regions during their long lifetime and are the principal participants in drift and diffusion at cryogenic temperatures. This insight supports proposals on the origin of single-photon sources in WSe and demonstrates a route towards exciton traps for exciton condensation.