In narrow electron bands where the Coulomb interaction energy becomes comparable to the bandwidth, interactions can drive new quantum phases. Such flat bands in twisted graphene-based systems result in correlated insulator, superconducting, and topological states. Here we report evidence of low energy flat bands in twisted bilayer WSe2, with signatures of collective phases observed over twist angles ranging from 4◦ to 5.1◦. At half band filling, a correlated insulator appears that is tunable with both twist angle and displacement field. At 5.1◦ twist, zero-resistance pockets are observed upon doping away from half filling, at temperatures below 3K, indicating a possible transition to a superconducting state. The observation of tunable collective phases in a simple band, which hosts only two holes per unit cell at full filling, establishes twisted bilayer transition metal dichalcogenides as an ideal platform to study correlated physics in 2D on a triangular lattice.

En-Min Shih

Columbia University