Topological superconductors, whose edge hosts Majorana bound states orMajorana fermions that obey non-Abelian statistics, can be used forlow-decoherence quantum computations. Most of the proposed topologicalsuperconductors are realized with spin-helical states through proximity effectto BCS superconductors. However, such approaches are difficult for furtherstudies and applications because of the low transition temperatures andcomplicated hetero-structures. Here by using high-resolution spin-resolved andangle-resolved photoelectron spectroscopy, we discover that the iron-basedsuperconductor FeTe1-xSex (x = 0.45, Tc = 14.5 K) hosts Dirac-cone typespin-helical surface states at Fermi level, which open an s-wave SC gap belowTc. Our study proves that the surface states of FeTe0.55Se0.45 are 2Dtopologically superconducting, and thus provides a simple and possibly high-Tcplatform for realizing Majorana fermions.
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