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

Abstract

Topological insulators are a new class of material1,2, that exhibit robust gapless surface states protected by time-reversal symmetry3,4. 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 fermions5, and Majorana zero modes6 that may find application in fault-tolerant quantum computation7,8. Inducing superconductivity on the topological surface states is a prerequisite for their experimental realization1,2. Here, by growing high-quality topological insulator Bi2Se3 films on a d-wave superconductor Bi2Sr2CaCu2O8+δ 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 15 meV. Interestingly, distinct from the d-wave pairing of Bi2Sr2CaCu2O8+δ, 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.