Superconductivity in the twisted bilayer transition metal dichalcogenide WSe₂

The observation of superconductivity and correlated insulating states in twisted bilayer graphene has brought to the forefront the topic of twisted systems. The reproducibility in graphene-based systems can be difficult, hence new materials possessing similar features, like transition metal dichalcogenides (TMD), are being considered.  The enhancement of electronic correlations by the introduction of a small twist angle between the two layers can be seen in a TMD bilayer such as twisted WSe2. Experimental observations in this TMD have revealed the presence of flat energy bands for a continuum of angles. Evidence of superconductivity was also reported (Wang, L. et al., Nat. Mater. 19, 861–866 (2020)). 

We report on an investigation of superconductivity within an effective Hubbard model defined on a triangular lattice for twisted WSe2. We use the variational cluster approximation (VCA) and cluster dynamical mean field theory (CDMFT) to take into account short-range correlations exactly, and work at zero temperature with an exact-diagonalization impurity solver. We find a superconducting phase of type d+id away from half-filling, that can be tuned by the twist angle and by the application of a perpendicular electric field.