Uniform Diffusion of Cooper Pairing Mediated by Hole Carriers in Topological Sb₂Te₃/Nb.

Abstract

Spin-helical Dirac Fermions at a doped topological insulator's boundaries can support Majorana quasiparticles when coupled with <i>s</i>-wave superconductors, but in <i>n</i>-doped systems, the requisite induced Cooper pairing in topological states is often buried at heterointerfaces or complicated by degenerate coupling with bulk conduction carriers. Rarely probed are <i>p</i>-doped topological structures with nondegenerate Dirac and bulk valence bands at the Fermi level, which may foster long-range superconductivity without sacrificing Majorana physics. Using ultrahigh-resolution photoemission, we report proximity pairing with a large decay length in <i>p</i>-doped topological Sb₂Te₃ on superconducting Nb. Despite no momentum-space degeneracy, the topological and bulk states of Sb₂Te₃/Nb exhibit the same isotropic superconducting gaps at low temperatures. Our results unify principles for realizing accessible pairing in Dirac Fermions relevant to topological superconductivity.