# Probing and dressing magnetic impurities in a superconductor

## TL;DR

This paper introduces a microwave-based method to probe and control magnetic impurity interactions in superconductors by utilizing Yu-Shiba-Rusinov states, enabling insights into magnetic order and potential applications in spin glasses.

## Contribution

It presents a novel technique to manipulate and measure magnetic impurity interactions in superconductors using microwave radiation and YSR states, offering new experimental possibilities.

## Key findings

- Microwave radiation can induce ferro- or antiferromagnetic interactions depending on detuning.
- Measurement of microwave response reveals magnetic order of impurities.
- Estimated microwave absorption and interaction strength are feasible for experimental realization.

## Abstract

We propose a method to probe and control the interactions between an ensemble of magnetic impurities in a superconductor via microwave radiation. Our method relies upon the presence of sub-gap Yu-Shiba-Rusinov (YSR) states associated with the impurities. Depending on the sign of the detuning, radiation generates either a ferro- or antiferromagnetic contribution to the exchange interaction. This contribution can bias the statistics of the random exchange constants stemming from the RKKY interaction. Moreover, by measuring the microwave response at the YSR resonance, one gains information about the magnetic order of the impurities. To this end, we estimate the absorption coefficient as well as the achievable strength of the microwave-induced YSR-interactions using off-resonant radiation. The ability to utilize microwave fields to both probe and control impurity spins in a superconducting host may open new paths to studying metallic spin glasses.