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_c) 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 Bi₂Sr₂CaCu₂O_8+δ (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_c 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_c, make this system a prime candidate for exploring stable Majorana fermions at very high temperatures.

中文翻译：

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高温铜酸盐超导体Bi ₂ Sr ₂ CaCu ₂ O _{8 +δ}作为拓扑超导体候选的超薄铋膜

凝聚态物理的主要挑战之一是要建立一种拓扑超导体，其中容纳了奇异的马约拉纳费米子。尽管已深入研究了由常规BCS（巴登-库珀-施里弗）超导体以及掺杂的拓扑绝缘体组成的各种异质结构，但并未提供马约拉那费米子的确凿证据。这主要是因为它们的超导转变温度（T _c）非常低，超导间隙幅值也很小。在这里，我们报告在Bi（110）超薄膜和氧化铜超导体Bi ₂ Sr ₂ CaCu ₂ O _{8 +δ}的混合物中，在非常高的温度下实现拓扑超导的可能实现（Bi2212）。使用角度分辨光发射光谱法和扫描隧道显微镜，我们发现Bi2212上三层厚的Bi（110）表现出近效应感应的s波能隙，最大为7.5 meV，一直持续到Bi2212的T _c为止。 （85 K）。Bi（110）的小费米能量和强自旋轨道耦合，以及大的配对间隙和较高的T _c，使该系统成为在高温下探索稳定的马里亚纳费米子的主要候选者。