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中国物理学会期刊

在人工拓扑超导体磁通涡旋中寻找Majorana零能模

CSTR: 32037.14.aps.68.20181698

Search for Majorana zero mode in the magnetic vortex of artificial topological superconductor

CSTR: 32037.14.aps.68.20181698
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  • 寻找具有拓扑序的新物质态是目前一个非常活跃和令人激动的研究领域. 与拓扑绝缘体类似, 在超导体中也存在着拓扑非平庸的超导态, 它与传统的超导体在拓扑性上是不等价的, 这种具有非平庸拓扑序的超导体被称为拓扑超导体. 拓扑超导体在体内具有非零的超导能隙, 而在表面有无能隙的表面态. 理论预言在拓扑超导体中能够实现具有非Abelian 统计特性的Majorana费米子. Majorana费米子可以用来构建拓扑量子比特, 在拓扑量子计算方面有重大的科研和应用前景. 拓扑绝缘体的出现催生出了许多人工拓扑超导体材料. 本专题将主要介绍在拓扑绝缘体/超导体异质结中探测Majorana费米子的一系列实验工作. 通过对拓扑超导体的研究, 人们对超导电性有了全新的认识, 有可能找到实现Majorana费米子新奇量子物理性质的方法.

     

    The search for new states that exhibit topological order is currently a very active and exciting area of research. Like a topological insulator, superconducting order can also exhibit topological order, which is different from that of a conventional superconductor. This superconductor is so-called " topological superconductor”, which has a full pairing gap in the bulk and gapless surface state. Majorana Fermions obey non-Abelian fractional statistics, and have been proposed to construct topological qubits, so there is a great prospect of scientific research and application in topological quantum computing. It is very interesting that Majorana Fermions are predicted to exist in topological superconductors. However, natural topological superconductor is very rare. Inspired by the realization of topological insulators, theoretical physicists have proposed that via the fabrication of the s-wave superconductor/topological insulator heterostructure, Majorana Fermions may exist in the superconducting topological insulator induced by proximate effect. Due to various kinds of topological insulators and conventional s-wave superconductors, heterostructures constructed by this method can greatly increase the variety of artificial topological superconductors. In this paper we review the experimental progress in the heterostructure composed of the Bi2Te3-type topological insulator and the conventional s-wave superconductor NbSe2. Using molecular beam epitaxy, atomically flat topological insulator film can be fabricated at the top of superconductor substrate. The spatial distribution of Majorana Fermions on the surface of topological insulator can be directly observed by in situ scanning tunneling microscopy/spectroscopy. In the center of a magnetic vortex, Majorana Fermions will appear as the Majorana zero mode, a zero-energy peak inside the superconducting gap. Although the energy gap between low energy quasiparticle excitation and the Majorana zero mode is very small, the evidences such as zero bias conductance anomaly, Y-shape splitting of zero-bias conductance, spin-selective Andreev reflection are self-consistent and reveal that the Majorana zero mode exists in the center of a magnetic vortex. These experiments have led to a new insight into superconductivity. It may open a door to probing the novel physics of Majorana fermions.

     

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