Title：Engineering electronic correlation and excitons in 2D moiré superlattices

Speaker：Yanhao Tang，Cornell University

Date：July 10, 2020 9:30 AM

Meeting Link：Tecent Meeting

https://meeting.tencent.com/s/CDlCZh11MeT8

Meeting ID: 831 835 820

Abstract：Van der Waals moiré superlattices, simply formed either by lattice mismatch or stacking angle, open an unprecedented opportunity for tailoring interactions between quantum particles and their coupling to electromagnetic field. Combining with tuning knobs like doping, electric and magnetic field, properties of moiré superlattices can be well controlled, which provide a model platform for investigating electron-electron correlation and its effects on optical properties. For example, magical-angle-twisted bilayer graphene (MATBG) has showed as an exotic phase factory, which holds Mott insulator, superconductivity and quantum anomalous hall. However, due to its complicated band structure and narrow window of magical angle, there is a demand for a complementary system. In this talk, I will show optical spectroscopy studies on 2D moiré superlattices based on transition metal dichalcogenides. I will first discuss a recent experimental realization of the two-dimensional triangular lattice Hubbard model in angle-aligned WSe2/WS2 moiré superlattices. We obtain a quantum phase diagram of the two-dimensional triangular lattice Hubbard model near v=1 filling by probing both the charge and magnetic order of the system [1]. Then I will discuss the observation of enhanced magnetic interaction at v=2/3 filling, and possible mechanism. Finally, I will discuss a direct observation of spatially mixed excitons in angle-aligned WSe2/WS2 and MoSe2/WS2 superlattices, where the energy of such mixed excitons can be widely tuned by electric field, with maintaining strong light-matter interaction [2].

[1] Tang, et al., Nature, 579, 353 (2020)

[2] Tang, et al., arXiv:2002.10067 (2020)