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

Zhang, Peng; Yaji, Koichiro; Hashimoto, Takahiro; Ota, Yuichi; Kondo, Takeshi; Okazaki, Kozo; Wang, Zhijun; Wen, Jinsheng et al. · Science · 2018

basic_science · Level V

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Abstract

Topological superconductors are predicted to host exotic Majorana states that obey non-Abelian statistics and can be used to implement a topological quantum computer. Most of the proposed topological superconductors are realized in difficult-to-fabricate heterostructures at very low temperatures. By using high-resolution spin-resolved and angle-resolved photoelectron spectroscopy, we find that the iron-based superconductor FeTe<sub>1-</sub><i><sub>x</sub></i> Se <i><sub>x</sub></i> (<i>x</i> = 0.45; superconducting transition temperature <i>T</i><sub>c</sub> = 14.5 kelvin) hosts Dirac-cone-type spin-helical surface states at the Fermi level; the surface states exhibit an s-wave superconducting gap below <i>T</i><sub>c</sub> Our study shows that the surface states of FeTe<sub>0.55</sub>Se<sub>0.45</sub> are topologically superconducting, providing a simple and possibly high-temperature platform for realizing Majorana states.