Yang Zhongzheng, Zheng Fanbang, Wu Dingsong, Zhang Bin-Bin, Li Ning, Li Wenhui, Zhang Chaofan, Zhang Guang-Ming, Chen Xi, Chen Yulin, Yan Shichao
State Key Laboratory of Quantum Functional Materials, School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China.
Department of Physics, University of Oxford, Oxford OX1 3PU, UK.
Natl Sci Rev. 2025 Jul 4;12(8):nwaf267. doi: 10.1093/nsr/nwaf267. eCollection 2025 Aug.
The recently discovered heavy-fermion superconductor, UTe, is an excellent candidate for spin-triplet superconductors in which electrons form spin-triplet Cooper pairs with spin = 1 and odd parity. Unconventional superconductivity often hosts unconventional vortices. Yet, the vortex core and lattice in UTe have not been directly visualized and characterized. Here, by using ultralow-temperature scanning tunnelling microscopy and spectroscopy, we study the superconducting vortices on the (0-11) surface termination of UTe with an out-of-plane external magnetic field. At the centre of the vortex core, we observe a robust zero-energy vortex-core state that exhibits a cigar-shaped spatial distribution and extends to ∼30 nm along the [100] direction (crystallographic -axis) of UTe. Along the direction perpendicular to [100], the superconducting gap is deeper and the coherence peak on one side of the vortex core is stronger than on the opposite side, and they are even enhanced in comparison with those under zero field. Due to the anisotropy of magnetic susceptibility in UTe, the asymmetric d/d spectra on the two sides of the vortex core result from the interplay between the magnetization-induced bound current and supercurrent around the vortex core. Our work reveals the important role of magnetization in the vortex behaviours of UTe and provides essential microscopic information for understanding its superconducting properties in a magnetic field.
最近发现的重费米子超导体UTe₂是自旋三重态超导体的极佳候选者，在这种超导体中，电子形成自旋为1且宇称奇的自旋三重态库珀对。非常规超导通常存在非常规涡旋。然而，UTe₂中的涡旋核心和晶格尚未得到直接成像和表征。在此，我们利用超低温扫描隧道显微镜和能谱，在面外外磁场下研究了UTe₂的(001)表面终端上的超导涡旋。在涡旋核心中心，我们观察到一个稳健的零能涡旋核心态，它呈现出雪茄形的空间分布，并沿UTe₂的[100]方向（结晶学a轴）延伸至约30纳米。沿垂直于[100]的方向，超导能隙更深，涡旋核心一侧的相干峰比另一侧更强，并且与零场下相比它们甚至增强了。由于UTe₂中磁化率的各向异性，涡旋核心两侧不对称的dI/dV能谱是由涡旋核心周围磁化诱导的束缚电流和超电流之间的相互作用导致的。我们的工作揭示了磁化在UTe₂涡旋行为中的重要作用，并为理解其在磁场中的超导特性提供了重要的微观信息。
