Richard L. Greene Dissertation Award Talk: Coherent Light-Matter Interactions in 2D Materials

Monolayer transition-metal dichalcogenides are prime examples of 2D semiconductors that exhibit remarkable electronic properties. They have a pair of electronic valleys that can serve as a new degree of freedom to carry information. However, these valleys are normally locked in the same energy level, which limits their potential use for applications. Here, we discuss a direct optical method to tune the exciton energy levels of monolayer WS₂ in a valley-selective manner through the optical Stark effect [1] and the Bloch-Siegert shift [2], performed at MIT. The two effects are found to obey opposite selection rules, which enables us to separate the two effects at two different valleys. Finally, I will briefly discuss our recent experiments where the topological phases of semimetal WTe₂ can be manipulated using light-induced atomic-scale lattice distortions [3], performed at SLAC/Stanford University.

References
[1] EJ Sie, JW McIver, YH Lee, L Fu, J Kong, N Gedik, Nature Materials 14, 290 (2015)
[2] EJ Sie, CH Lui, YH Lee, L Fu, J Kong, N Gedik, Science 355, 1066 (2017)
[3] EJ Sie, CM Nyby, AM Lindenberg et al, Nature (2019)