近日，清华大学的宋灿立&薛其坤及其研究团队与中国科学院苏州纳米技术与纳米仿生研究所的李坊森等人合作并取得一项新进展。经过不懈努力，他们揭示K₃C₆₀中量子自旋驱动的Yu-Shiba-Rusinov多重态和费米子宇称守恒的相变。相关研究成果已于2024年3月27日在国际知名学术期刊《科学通报》上发表。

该研究团队利用扫描隧道显微技术，系统地分析了K₃C₆₀超导体中单个过渡金属(Fe、Cr和Ni)杂质诱导的YSR多重态及其塞曼效应。YSR多重态展现出了与三重K₃C₆₀(111)主表面在对称性上不匹配的相似d轨道波函数特征，这一特性打破了YSR束缚态在实空间分布中的点群对称性。

值得一提的是，研究团队在具有相反单轴磁各向异性符号的基态之间，首次观测到了费米子宇称守恒的量子相变现象，该相变可以通过外部磁场进行调控。这些发现可以从量子杂质自旋各向异性分裂的角度得到合理解释，进而揭示了磁各向异性与YSR多重态之间错综复杂的相互作用关系。

据悉，由于在容错量子计算中出现了Yu-Shiba-Rusinov (YSR)态和马约拉纳零模式，超导体中的磁性杂质越来越引起人们的兴趣。然而，YSR多重态与量子杂质自旋磁各向异性分裂之间的直接关系仍然缺乏表征。

附：英文原文

Title: Quantum spin driven Yu-Shiba-Rusinov multiplets and fermion-parity-preserving phase transition in K₃C₆₀

Author: Shu-Ze Wang1†, Xue-Qing Yu1†, Li-Xuan Wei1, Li Wang2, Qiang-Jun Cheng1, Kun Peng2, Fang-Jun Cheng1, Yu Liu1, Fang-Sen Li2*, Xu-Cun Ma1,3, Qi-Kun Xue1,3,4,5*, Can-Li Song1,3*

Issue&Volume: 2024/03/27

Abstract: Magnetic impurities in superconductors are of increasing interest due to emergent Yu-Shiba-Rusinov (YSR) states and Majorana zero modes for fault-tolerant quantum computation. However, a direct relationship between the YSR multiple states and magnetic anisotropy splitting of quantum impurity spins remains poorly characterized. By using scanning tunneling microscopy, we resolve systematically individual transition-metal (Fe, Cr and Ni) impurities induced YSR multiplets as well as their Zeeman effects in K₃C₆₀ superconductor. The YSR multiplets show identical d orbital-like wave functions that are symmetry-mismatched to the threefold K₃C₆₀(111) host surface, breaking point-group symmetries of the spatial distribution of YSR bound states in real space. Remarkably, we identify an unprecedented fermion-parity-preserving quantum phase transition between ground states with opposite signs of the uniaxial magnetic anisotropy that can be manipulated by an external magnetic field. These findings can be readily understood in terms of anisotropy splitting of quantum impurity spins, and thus elucidate the intricate interplay between the magnetic anisotropy and YSR multiplets.

DOI: 10.1016/j.scib.2024.03.052

Source: https://www.sciencedirect.com/science/article/abs/pii/S2095927324002081