近日，德国科隆大学的Yoichi Ando&A. A. Taskin及其研究团队取得一项新进展。经过不懈努力，他们揭示量子反常霍尔绝缘体中的诱导超导相关性。相关研究成果已于2024年7月10日在国际知名学术期刊《自然—物理学》上发表。

该研究团队展示了交叉安德烈夫反射在与量子反常霍尔绝缘体的手性边缘态接触的窄超导铌电极上。在交叉安德烈夫反射过程中，从一端注入的电子在另一端作为空穴反射出去，在超导体中形成库珀对。这是手性边缘态诱导超导配对相关的一个令人信服的特征。交叉安德烈夫反射过程的特征长度远大于铌中的超导相干长度，这表明交叉安德烈夫反射确实是由量子反常霍尔绝缘体表面诱导的超导介导的。

这项研究结果将为未来的拓扑超导和马约拉纳物理的研究，以及对非阿贝尔零模式的研究提供了基础。

据悉，铁磁拓扑绝缘体材料薄膜可以在不需要外加磁场的情况下承载量子反常霍尔效应。在这种材料中诱导库柏配对是一种，很有希望实现具有相关手性马约拉纳边态的拓扑超导性的方法。然而，由于固有的实验困难，在这种状态下寻找超导邻近效应的证据仍然是一个相当大的挑战。

附：英文原文

Title: Induced superconducting correlations in a quantum anomalous Hall insulator

Author: Uday, Anjana, Lippertz, Gertjan, Moors, Kristof, Legg, Henry F., Joris, Rikkie, Bliesener, Andrea, Pereira, Lino M. C., Taskin, A. A., Ando, Yoichi

Issue&Volume: 2024-07-10

Abstract: Thin films of ferromagnetic topological insulator materials can host the quantum anomalous Hall effect without the need for an external magnetic field. Inducing Cooper pairing in such a material is a promising way to realize topological superconductivity with the associated chiral Majorana edge states. However, finding evidence of the superconducting proximity effect in such a state has remained a considerable challenge due to inherent experimental difficulties. Here we demonstrate crossed Andreev reflection across a narrow superconducting Nb electrode that is in contact with the chiral edge state of a quantum anomalous Hall insulator. In the crossed Andreev reflection process, an electron injected from one terminal is reflected out as a hole at the other terminal to form a Cooper pair in the superconductor. This is a compelling signature of induced superconducting pair correlation in the chiral edge state. The characteristic length of the crossed Andreev reflection process is found to be much longer than the superconducting coherence length in Nb, which suggests that the crossed Andreev reflection is, indeed, mediated by superconductivity induced on the quantum anomalous Hall insulator surface. Our results will invite future studies of topological superconductivity and Majorana physics, as well as for the search for non-abelian zero modes.

DOI: 10.1038/s41567-024-02574-1

Source: https://www.nature.com/articles/s41567-024-02574-1