Realizing Majorana zero modes by proximity effect between topological insulators and d-wave high-temperature superconductors

We theoretically study the superconducting proximity effect between a topological insulator (TI) and a hightemperature d-wave superconductor (dSC). When the TI-dSC heterostructure violates 90. rotation and certain reflection symmetries, we show that a sizable s-wave pairing, coexisting with a d-wave one, emerges in the proximity-induced superconductivity in the TI's top surface states. Weak disorder further suppresses d-wave pairing (but not s-wave pairing) in the TI's surface states. More importantly, the pairing gap in the surface states is found to be nodeless and nearly isotropic when the Fermi pocket of surface states is relatively small. Our theoretical results qualitatively explain recent experimental evidences of a nearly-isotropic pairing gap on surface states of Bi2Se3 induced by proximity to high-Tc cuprate Bi2Ca2Cu2O8+delta. We also demonstrate convincing evidence of Majorana zero modes in a magnetic hc/2e vortex core which may be detectable in future experiments.