Li Yuanji, Yin Ruotong, Li Mingzhe, Gong Jiashuo, Chen Ziyuan, Zhang Jiakang, Yan Ya-Jun, Feng Dong-Lai
School of Emerging Technology and Department of Physics, University of Science and Technology of China, Hefei, 230026, China.
Hefei National Laboratory, University of Science and Technology of China, Hefei, 230088, China.
Nat Commun. 2024 Nov 22;15(1):10121. doi: 10.1038/s41467-024-54525-2.
The hybrid ferromagnet-superconductor heterostructures have attracted extensive attention as they potentially host topological superconductivity. Relevant experimental signatures have recently been reported in CrBr/NbSe ferromagnet-superconductor heterostructure, but controversies remain. Here, we reinvestigate CrBr/NbSe by an ultralow temperature scanning tunneling microscope with higher spatial and energy resolutions. We find that the single-layer CrBr film is insulating and acts likely as a vacuum barrier, the measured superconducting gap and vortex state on it are nearly the same as those of NbSe substrate. Meanwhile, in-gap features are observed at the edges of CrBr island, which display either a zero-energy conductance peak or a pair of particle-hole symmetric bound states. They are discretely distributed at the edges of CrBr film, and their appearance is found closely related to the atomic lattice reconstruction near the edges. By increasing tunneling transmissivity, the zero-energy conductance peak quickly splits, while the pair of nonzero in-gap bound states first approach each other, merge, and then split again. These behaviors are unexpected for Majorana edge modes, but in consistent with the conventional Yu-Shiba-Rusinov states. Our results provide critical information for further understanding the interfacial coupling in CrBr/NbSe heterostructure.
混合铁磁体-超导体异质结构因其可能存在拓扑超导性而受到广泛关注。最近在CrBr/NbSe铁磁体-超导体异质结构中报道了相关的实验特征，但仍存在争议。在此，我们使用具有更高空间和能量分辨率的超低温扫描隧道显微镜对CrBr/NbSe进行了重新研究。我们发现单层CrBr薄膜是绝缘的，并且可能起到真空势垒的作用，在其上测量的超导能隙和涡旋态与NbSe衬底的几乎相同。同时，在CrBr岛的边缘观察到了能隙内特征，其表现为零能电导峰或一对粒子-空穴对称束缚态。它们离散地分布在CrBr薄膜的边缘，并且发现它们的出现与边缘附近的原子晶格重构密切相关。通过增加隧穿透射率，零能电导峰迅速分裂，而一对非零能隙束缚态首先相互靠近、合并，然后再次分裂。这些行为对于马约拉纳边缘模式来说是出乎意料的，但与传统的宇-芝-鲁西诺夫态一致。我们的结果为进一步理解CrBr/NbSe异质结构中的界面耦合提供了关键信息。
