The role and impact of spatial heterogeneity in two-dimensional quantum materials represents one of the major research quests regarding the future application of these materials in optoelectronics and quantum information science. In the case of transition-metal dichalcogenide heterostructures, in particular, direct access to heterogeneities in the dark-exciton landscape with nanometer spatial and ultrafast time resolution is highly desired, but remains largely elusive. Here, we introduce ultrafast dark field momentum microscopy to spatio-temporally resolve dark exciton formation dynamics in a twisted WSe2/MoS2 heterostructure with 55 femtosecond time- and 500~nm spatial resolution. This allows us to directly map spatial heterogeneity in the electronic and excitonic structure, and to correlate these with the dark exciton formation and relaxation dynamics. The benefits of simultaneous ultrafast nanoscale dark-field momentum microscopy and spectroscopy is groundbreaking for the present study, and opens the door to new types of experiments with unprecedented spectroscopic and spatiotemporal capabilities.
@article{arxiv.2305.18908,
title = {Ultrafast nano-imaging of dark excitons},
author = {David Schmitt and Jan Philipp Bange and Wiebke Bennecke and Giuseppe Meneghini and AbdulAziz AlMutairi and Marco Merboldt and Jonas Pöhls and Kenji Watanabe and Takashi Taniguchi and Sabine Steil and Daniel Steil and R. Thomas Weitz and Stephan Hofmann and Samuel Brem and G. S. Matthijs Jansen and Ermin Malic and Stefan Mathias and Marcel Reutzel},
journal= {arXiv preprint arXiv:2305.18908},
year = {2025}
}