Emergent electronic structure and optical properties in two-dimensional materials

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As a new member of the two dimensional material family, the transition metal dichalcogenide (TMDC) has attracted a lot of interest because many new fascinating physical properties start to emerge at the monolayer limit, such as a direct band gap at the edge of Brillion zone, extraordinarily intense light-matter interaction, access to the valley degree of freedom, and unusually strong Coulomb interaction with reduced screening. In the past, we have discovered a tightly bound exciton stable even at room temperature in TMDC monolayer and successfully controlled its valley coherence using ultrafast light. These extraordinary properties, together with the flexible nature of the material, have triggered tremendous interest in device applications such as flexible screens and touchpads. In this proposed program, our main focus is to explore more emergent phenomena such as the topological Moiré pattern, single photon emitter, and steady Floquet state in 2D TMDCs and related heterostructures towards quantum information applications. We are particularly interested in employing new experimental techniques such as photoinduced force microscopy, ultrafast laser with tunable pulse duration, and high-Q optical micro cavity to study TMDCs in the intense optical field with sub-diffractional spatial resolution. Within the next five years, we will investigate a series of open questions such as the formation mechanism behind the TMDC quantum dot, the impact of Moiré pattern on the optical property of TMDC heterostructures, and the thermalization process of Floquet states. Moreover, we will demonstrate some new control possibilities including the full valley pseudospin manipulation, tunable topological insulator nanostructure array, and the optical induced topologically nontrivial steady Floquet state. A new type of surface-plasmon assisted optical nearfield probe is also in our development plan. The proposed research will have a large impact in physics, material science engineering, and electrical engineering. On the one hand, our study will provide fundamental understanding of topological effects and nonequilibrium physics in solids. The deep insights obtained for TMDCs will help further improve the performance of 2D material/heterostructure based devices. On the other hand, the proposed emergent phenomena are promising to be combined with the spin and valley degrees of freedom to enable scalable quantum information processing in an integrated platform.