Complete band structure of microscopic MoS₂and WSe₂flakes

Transition-metal dichalcogenides (TMDC) have a MX₂ layered structure with 2H symmetry and M = Mo, W; X = S, Se, Te etc. They occupy a unique place in the class of two-dimensional materials thanks to their fascinating electronic properties [1]. Recently, it has been predicted theoretically = that a topological phase transition can be induced entirely with shaped light fields, such as trefoil polarization states, in conventional hexagonal materials [2]. This opens a route towards a new device based on creating a topologically protected electronic state using ultrashort structured light pulses. By orienting the trefoil symmetry it is possible to populate alternatively K and K’ valleys in the conduction band. With this in mind, we experimentally determined the complete band structure (both occupied and unoccupied states) of single crystal microscopicTMDC flakes using full k-space imaging of photoemission electron microscopy and secondary electron emission, following ref [3]. These results allowed us to accurately calculate the valence and conduction band structures in a single photoemission experiment and are compared with first-principles calculations. They will be used in future pump-probe experiments to explore the electron dynamics in the conduction band and photo-induced multi-topological states.

[1] S. Manzeli et al., Nat. Rev. Mat. 2, 17033 (2017)

[2] R. E. F. Silva et al., Nat. Phot. 13, 849–854 (2019)

[3] G. Wan et al., Adv. Funct. Mater. 31, 2007319 (2021)