Topological superconductivity from repulsive interactions in twisted WSe$_2$

Abstract

The recent observation of superconductivity in twisted bilayer WSe$_2$ raises intriguing questions concerning the origin and the properties of superconducting states realized in bands with non-trivial topological properties and repulsive electron-electron interactions. Using a continuum band structure model, we analyze a mechanism for Coulomb interaction-driven superconductivity in twisted bilayers of WSe$_2$. We discuss the symmetries and the phenomenological properties of the resulting superconducting phases and their evolution with interlayer potential difference, tunable via an out of plane electric field. The pairing strength is a non-monotonic function of interlayer potential, being larger at intermediate values due to mixing of singlet and triplet pairing. In contrast, at larger interlayer potential, the pairing tendency is suppressed due to enhanced Coulomb repulsion. The superconducting state is chiral in a large regime of parameters and undergoes a transition to a nodal nematic superconductor at a critical potential difference. The chiral state, characterized by an intervalley-symmetric superposition of triplet and singlet pairs, is classified as a topological superconductor within the Altland-Zirnbauer class C. At zero interlayer potential difference, the superconducting state is instead of class D, which hosts Majorana zero modes, making it a promising candidate for applications in quantum computation.