Huang Ce, Narayan Awadhesh, Zhang Enze, Liu Yanwen, Yan Xiao, Wang Jiaxiang, Zhang Cheng, Wang Weiyi, Zhou Tong, Yi Changjiang, Liu Shanshan, Ling Jiwei, Zhang Huiqin, Liu Ran, Sankar Raman, Chou Fangcheng, Wang Yihua, Shi Youguo, Law Kam Tuen, Sanvito Stefano, Zhou Peng, Han Zheng, Xiu Faxian
State Key Laboratory of Surface Physics and Department of Physics , Fudan University , Shanghai 200433 , China.
Institute for Nanoelectronic Devices and Quantum Computing , Fudan University , Shanghai 200433 , China.
ACS Nano. 2018 Jul 24;12(7):7185-7196. doi: 10.1021/acsnano.8b03102. Epub 2018 Jun 21.
The search for proximity-induced superconductivity in topological materials has generated widespread interest in the condensed matter physics community. The superconducting states inheriting nontrivial topology at interfaces are expected to exhibit exotic phenomena such as topological superconductivity and Majorana zero modes, which hold promise for applications in quantum computation. However, a practical realization of such hybrid structures based on topological semimetals and superconductors has hitherto been limited. Here, we report the strong proximity-induced superconductivity in type-II Weyl semimetal WTe, in a van der Waals hybrid structure obtained by mechanically transferring NbSe onto various thicknesses of WTe. When the WTe thickness ( t) reaches 21 nm, the superconducting transition occurs around the critical temperature ( T) of NbSe with a gap amplitude (Δ) of 0.38 meV and an unexpected ultralong proximity length ( l) up to 7 μm. With the thicker 42 nm WTe layer, however, the proximity effect yields T ≈ 1.2 K, Δ = 0.07 meV, and a short l of less than 1 μm. Our theoretical calculations, based on the Bogoliubov-de Gennes equations in the clean limit, predict that the induced superconducting gap is a sizable fraction of the NbSe superconducting one when t is less than 30 nm and then decreases quickly as t increases. This agrees qualitatively well with the experiments. Such observations form a basis in the search for superconducting phases in topological semimetals.
在拓扑材料中寻找近邻诱导超导性已在凝聚态物理领域引起广泛关注。人们期望在界面处继承非平凡拓扑结构的超导态能展现出诸如拓扑超导和马约拉纳零模等奇异现象，这为量子计算的应用带来了希望。然而，迄今为止，基于拓扑半金属和超导体的此类混合结构的实际实现仍很有限。在此，我们报道了在通过将NbSe机械转移到不同厚度的WTe上获得的范德华混合结构中，II型外尔半金属WTe中存在强近邻诱导超导性。当WTe厚度（t）达到21纳米时，超导转变发生在NbSe的临界温度（T）附近，能隙幅度（Δ）为0.38毫电子伏特，且出现了高达7微米的意外超长近邻长度（l）。然而，对于更厚的42纳米WTe层，近邻效应产生的T约为1.2开尔文，Δ = 0.07毫电子伏特，且近邻长度l小于1微米。我们基于清洁极限下的博戈留波夫 - 德热纳方程进行的理论计算预测，当t小于30纳米时，诱导超导能隙是NbSe超导能隙的相当一部分，然后随着t增加而迅速减小。这与实验结果在定性上吻合得很好。此类观测结果为在拓扑半金属中寻找超导相奠定了基础。
