Emergent surface superconductivity of nanosized Dirac puddles in a topological insulator

Abstract

Surfaces of three-dimensional topological insulators have emerged as one of the most remarkable states of condensed quantum matter1-5 where exotic electronic phases of Dirac particles should arise1,6-8. Here we report a discovery of surface superconductivity in a topological material (Sb2Te3) with resistive transition at a temperature of ~9 K induced through a minor tuning of growth chemistry that depletes bulk conduction channels. The depletion shifts Fermi energy towards the Dirac point as witnessed by about two orders of magnitude reduction of carrier density and by very large (~25,000 cm^2/Vs) carrier mobility. Direct evidence from scanning tunneling spectroscopy and from magnetic response show that the superconducting condensate forms in surface puddles at unprecedentedly higher temperatures, near 60 K and above. The new superconducting state we observe to emerge in puddles can be tuned by the topological material's parameters such as Fermi velocity and mean free path through band engineering; it could potentially become a hunting ground for Majorana modes6 and lead to a disruptive paradigm change9 in how quantum information is processed.