Combinatorics

Physics

Bound state

Topology (electrical circuits)

Fermi surface

MAJORANA

Mathematics

Photoemission spectroscopy

Topological insulator

Neutrino

Surface (topology)

Geometry

Condensed matter physics

Majorana fermion

Spin (aerodynamics)

Spectral line

Fermion

Superconductivity

Dirac (video compression format)

Quantum mechanics

Surface states

Thermodynamics

Science

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.

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