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Electron correlation and topology are two major themes of modern condensed matter physics. The magic angle twisted graphene (MATG) moiré superlattice features extremely flat energy bands, emerging as a new and highly tunable platform to study strongly correlated and topological quantum states, such as superconductivity, correlated insulators, quantum anomalous Hall effect, etc. The mechanism underlying these quantum phases has attracted intense interests. In this talk, I will present a novel van der Waals heterostructure, where the magic-angle twisted graphene and a Bernal bilayer graphene (BLG) are separated by an insulating barrier (hBN) with the thickness of only 2 ~ 3 nm. Benefiting from the charge screening effect from the nearby BLG, the strength of Coulomb interactions within the magic-angle twisted graphene can be continuously tuned. We have systematically studied the influence of the strength of Coulomb interaction on the stability of the superconductivity and correlated insulating states in MATG. Our findings not only provide the important theoretical constraints on understanding the nature of superconductivity in twisted graphene moiré systems, but also pave the way towards discovering, understanding, and manipulating more exotic phases based on the versatile 2D van der Waals heterostructures.
Xiaoxue Liu got her PhD in 2018 from Peking University, under the supervision of Prof. Rui-Rui Du. She is currently a postdoctoral researcher at Brown University working with Prof. Jia Leo Li. Her research interest is to explore and understand exotic quantum phases of matter based on low-dimensional materials, such as twisted graphene moiré systems and 2D semiconductor quantum wells. The research topics include strongly correlated phases, superconductivity, exciton condensation and fractional quantum hall states.