Higher-Order Topological Superconductivity with S-wave Pairing in Twisted Bilayer Graphene

We demonstrate that introducing s-wave superconductivity into twisted bilayer graphene induces symmetry-protected higher-order topological superconductivity. Multiple Majorana zero modes are bound to $C_{2x}$-protected corners of the sample. Using the Dirac Hamiltonian for twisted bilayer graphene, we explicitly construct Hamiltonians describing the edge and demonstrate the existence of corner modes at domain walls, provided the appropriate symmetries are preserved. We characterize the superconductor using the Wilson loop formalism and prove it is anomalous, and verify the presence of corner states with numerics. Finally, we study the fate of the Majorana zero modes in the presence of interactions, and suggest experimental setups to detect the topological superconductivity.