Observation of topological superconductivity on the surface of an iron-based superconductor

TLDR

Topological superconductors host Majorana bound states useful for quantum computing, but most realizations rely on proximity-induced spin‑helical states in BCS superconductors, which suffer from low transition temperatures and complex heterostructures. High‑resolution spin‑ and angle‑resolved photoelectron spectroscopy reveals that FeTe₀.₅₅Se₀.₄₅ possesses Dirac‑cone spin‑helical surface states that acquire an s‑wave superconducting gap below 14.5 K, demonstrating two‑dimensional topological superconductivity and offering a simple, potentially high‑Tc platform for Majorana fermions.

Abstract

Topological superconductors, whose edge hosts Majorana bound states or Majorana fermions that obey non-Abelian statistics, can be used for low-decoherence quantum computations. Most of the proposed topological superconductors are realized with spin-helical states through proximity effect to BCS superconductors. However, such approaches are difficult for further studies and applications because of the low transition temperatures and complicated hetero-structures. Here by using high-resolution spin-resolved and angle-resolved photoelectron spectroscopy, we discover that the iron-based superconductor FeTe1-xSex (x = 0.45, Tc = 14.5 K) hosts Dirac-cone type spin-helical surface states at Fermi level, which open an s-wave SC gap below Tc. Our study proves that the surface states of FeTe0.55Se0.45 are 2D topologically superconducting, and thus provides a simple and possibly high-Tc platform for realizing Majorana fermions.