In superconductors, magnetic impurities induce a pair-breaking potential for Cooper pairs, which locally affects the Bogoliubov quasiparticles and gives rise to Yu-Shiba-Rusinov (YSR or Shiba, in short) bound states in the density of states (DoS). These states carry information on the magnetic coupling strength of the impurity with the superconductor, which determines the many-body ground state properties of the system. Recently, the interest in Shiba physics was boosted by the prediction of topological superconductivity and Majorana modes in magnetically coupled chains and arrays of Shiba impurities. Here, we review the physical insights obtained by scanning tunneling microscopy into single magnetic adsorbates on the $s$-wave superconductor lead (Pb). We explore the tunneling processes into Shiba states, show how magnetic anisotropy affects many-body excitations, and determine the crossing of the many-body groundstate through a quantum phase transition. Finally, we discuss the coupling of impurities into dimers and chains and their relation to Majorana physics.

中文翻译：

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单磁吸附在 s 波超导体上

在超导体中，磁性杂质会引起库珀对的对断裂电位，这会局部影响 Bogoliubov 准粒子并在态密度 (DoS) 中产生 Yu-Shiba-Rusinov（简称 YSR 或 Shiba）束缚态。这些状态携带有关杂质与超导体的磁耦合强度的信息，这决定了系统的多体基态特性。最近，对磁耦合链和 Shiba 杂质阵列中的拓扑超导性和 Majorana 模式的预测提高了对 Shiba 物理学的兴趣。在这里，我们回顾了通过将隧道显微镜扫描到 $s$-波超导体引线 (Pb) 上的单个磁性吸附物而获得的物理见解。我们探索进入 Shiba 状态的隧道过程，展示磁各向异性如何影响多体激发，并通过量子相变确定多体基态的交叉。最后，我们讨论了杂质与二聚体和链的耦合及其与马约拉纳物理学的关系。