Fully gapped topological surface states in Bi2Se3 films induced by a d-wave high-temperature superconductor

Topological insulators are a newclass of material(1,2), that exhibit robust gapless surface states protected by time-reversal symmetry(3,4). The interplay of such symmetry-protected topological surface states and symmetry-broken states (for example, superconductivity) provides a platform for exploring new quantum phenomena and functionalities, such as one-dimensional chiral or helical gapless Majorana fermions(5), and Majorana zero modes(6) that may find application in fault-tolerant quantum computation(7,8). Inducing superconductivity on the topological surface states is a prerequisite for their experimental realization(1,2). Here, by growing high-quality topological insulator Bi2Se3 films on a d-wave superconductor Bi2Sr2CaCu2O8+delta using molecular beam epitaxy, we are able to induce high-temperature superconductivity on the surface states of Bi2Se3 films with a large pairing gap up to 15meV. Interestingly, distinct from the d-wave pairing of Bi2Sr2CaCu2O8-delta, the proximity-induced gap on the surface states is nearly isotropic and consistent with predominant s-wave pairing as revealed by angle-resolved photoemission spectroscopy. Our work could provide a critical step towards the realization of the long sought Majorana zero modes.