Magic continuum in twisted bilayer WSe2

TL;DR

This study reports the discovery of correlated insulating and superconducting states in twisted bilayer WSe2 across a continuum of twist angles, demonstrating tunable quantum phases in a semiconducting TMD system.

Contribution

It provides the first experimental observation of correlated phenomena over a broad range of twist angles in twisted bilayer WSe2, expanding the understanding of flat band physics beyond graphene.

Findings

Correlated insulator observed at half band filling.

Superconductivity evidenced near 5.1 degrees twist angle.

Insulator strength correlates with density of states at half filling.

Abstract

Emergent quantum phases driven by electronic interactions can manifest in materials with narrowly dispersing, i.e. "flat", energy bands. Recently, flat bands have been realized in a variety of graphene-based heterostructures using the tuning parameters of twist angle, layer stacking and pressure, and resulting in correlated insulator and superconducting states. Here we report the experimental observation of similar correlated phenomena in twisted bilayer tungsten diselenide (tWSe2), a semiconducting transition metal dichalcogenide (TMD). Unlike twisted bilayer graphene where the flat band appears only within a narrow range around a "magic angle", we observe correlated states over a continuum of angles, spanning 4 degree to 5.1 degree. A Mott-like insulator appears at half band filling that can be sensitively tuned with displacement field. Hall measurements supported by ab initio calculations suggest that the strength of the insulator is driven by the density of states at half filling, consistent with a 2D Hubbard model in a regime of moderate interactions. At 5.1 degree twist, we observe evidence of superconductivity upon doping away from half filling, reaching zero resistivity around 3 K. Our results establish twisted bilayer TMDs as a model system to study interaction-driven phenomena in flat bands with dynamically tunable interactions.