Nematic Superconductivity

Nematic superconductivity refers to the spontaneous breaking of rotational symmetry of a system in superconducting state. Nematic superconductivity in topological insulator Bi2Se3 doped with Cu, Nb, or Sr atoms was observed in numerous experiments, including Kinght shift, upper critical field, specific heat, magnetic torque, and STM measurements. Remarkably, such a nematic state appears to be a clear signature of topological superconductivity. In this talk, I will discuss the theoretically predicted properties of these compounds and their relation to the existing experiments. Furthermore, the recent measurements of the upper critical field in twisted bilayer graphene revealed strong two-fold anisotropy of the superconducting state, indicating nematic superconductivity. Motivated by these experiments, I will also briefly describe some theoretical proposals aiming to explain such an exotic state.