Unconventional superconductivity in twisted bilayer WSe2

TL;DR

This paper reports the discovery of robust superconductivity in twisted bilayer WSe2, a semiconductor moiré material, revealing strong correlation effects and a transition to an insulator, expanding understanding beyond graphene-based systems.

Contribution

It demonstrates superconductivity in twisted bilayer WSe2 with a flat Chern band, highlighting strong correlations and a continuous transition to an insulator, which is novel for semiconductor moiré materials.

Findings

Superconductivity observed at 220 mK in twisted bilayer WSe2.

Superconductivity occurs near half-band filling with a flat Chern band.

Transition to a correlated insulator by tuning sublattice potential.

Abstract

Moir\'e materials have enabled the realization of flat electron bands and quantum phases that are driven by strong correlations associated with flat bands. Superconductivity has been observed, but solely, in graphene moir\'e materials. The absence of robust superconductivity in moir\'e materials beyond graphene, such as semiconductor moir\'e materials, has remained a mystery and challenged our current understanding of superconductivity in flat bands. Here, we report the observation of robust superconductivity in 3.65-degree twisted bilayer WSe2 which hosts a honeycomb moir\'e lattice. Superconductivity emerges at half-band filling and under small sublattice potential differences, where the moir\'e band is a flat Chern band. The optimal superconducting transition temperature is about 220 mK and constitutes 2% of the effective Fermi temperature; the latter is comparable to the value in high-temperature cuprate superconductors and suggests strong pairing. The superconductor borders on two distinct metals below and above half-band filling; it undergoes a continuous transition to a correlated insulator by tuning the sublattice potential difference. The observed superconductivity on the verge of Coulomb-induced charge localization suggests roots in strong electron correlations.