Ultrathin Bismuth Film on High-Temperature Cuprate Superconductor Bi 2 Sr 2 CaCu 2 O 8+δ as a Candidate of a Topological Superconductor

• Published in: ACS nano 2018-11, Vol.12 (11), p.10977-10983
• Main Authors: Shimamura, Natsumi, Sugawara, Katsuaki, Sucharitakul, Sukrit, Souma, Seigo, Iwaya, Katsuya, Nakayama, Kosuke, Trang, Chi Xuan, Yamauchi, Kunihiko, Oguchi, Tamio, Kudo, Kazutaka, Noji, Takashi, Koike, Yoji, Takahashi, Takashi, Hanaguri, Tetsuo, Sato, Takafumi
• Format: Article
• Language: English
• ISSN: 1936-0851; 1936-086X
• DOI: 10.1021/acsnano.8b04869

One of the key challenges in condensed-matter physics is to establish a topological superconductor that hosts exotic Majorana fermions. Although various heterostructures consisting of conventional BCS (Bardeen-Cooper-Schrieffer) superconductors as well as doped topological insulators were intensively investigated, no conclusive evidence for Majorana fermions has been provided. This is mainly because of their very low superconducting transition temperatures ( T ) and small superconducting-gap magnitude. Here, we report a possible realization of topological superconductivity at very high temperatures in a hybrid of Bi(110) ultrathin film and copper oxide superconductor Bi Sr CaCu O (Bi2212). Using angle-resolved photoemission spectroscopy and scanning tunneling microscopy, we found that three-bilayer-thick Bi(110) on Bi2212 exhibits a proximity-effect-induced s-wave energy gap as large as 7.5 meV which persists up to T of Bi2212 (85 K). The small Fermi energy and strong spin-orbit coupling of Bi(110), together with the large pairing gap and high T , make this system a prime candidate for exploring stable Majorana fermions at very high temperatures.