# Single magnetic adsorbates on s-wave superconductors

## TL;DR

This paper reviews how single magnetic adsorbates on s-wave superconductors create Yu-Shiba-Rusinov states, revealing insights into magnetic interactions, anisotropy effects, quantum phase transitions, and potential links to Majorana modes.

## Contribution

It provides a comprehensive review of scanning tunneling microscopy studies on magnetic impurities in s-wave superconductors, highlighting new understanding of Shiba states and their role in topological superconductivity.

## Key findings

- Identification of Shiba states via STM.
- Effects of magnetic anisotropy on excitations.
- Observation of quantum phase transitions.

## Abstract

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.