Investigation of the Yu-Shiba-Rusinov states of a multi-impurity Kondo system

Understand

Recent studies of mutually interacting magnetic atoms coupled to a superconductor have gained enormous interest due to the potential realization of topological superconductivity.

• The Kondo exchange coupling J_K of such atoms with the electrons in the superconductor has a pair-breaking effect which produces so-called Yu-Shiba-Rusinov (YSR) states within the superconducting energy gap, whose energetic positions are intimately connected with the requirements for topological superconductivity.
• Here, using the tip of a scanning tunneling microscope, we artificially craft a multi-impurity Kondo system coupled to a superconducting host consisting of an Fe adatom interacting with an assembly of interstitial Fe atoms on an oxygen-reconstructed Ta(100) surface and we experimentally investigate the signatures of Kondo screening and the YSR states.
• With the help of numerical renormalization group (NRG) calculations, we show that the observed behavior can be qualitatively reproduced by a two-impurity Kondo system whose inter-impurity antiferromagnetic interaction J is adjusted by the number of interstitial Fe atoms in the assembly.