Special Seminar-Dicke Candidate-Shaowen Chen-Columbia University-"Tunable Correlated States in Twisted Graphene""-2:00 PM-Jadwin Room 303

Tue, Dec 17, 2019, 2:00 pm to 3:00 pm

Magic angle twisted graphene hosts low energy flat band as a result of interlayer hybridization. In the flat band Coulomb interaction is large relative to the bandwidth, promoting a collection of correlated insulating (CI) states at commensurate partial band filling, superconducting (SC) phases with dome-like structure, ferromagnetism and even quantum anomalous Hall effect. In the meantime, the system is highly tunable with experimental knobs such as interlayer pressure, displacement field and twist angle. I will first discuss using pressure to reduce the bandwidth of twisted bilayer graphene at larger than the magic angle. Using the transition temperatures of CI and SC we show by changing interlayer hybridization with pressure, the bandwidth can be controlled. I will also show recent results in twisted monolayer-bilayer ("2+1") graphene. Due to the reduced symmetry the displacement field can tune the bandwidth into different regimes, promoting distinct correlated states. Finally, I will talk about a new technique which makes it possible to continuously tune the twist angle between van der Waals materials.

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