Yu-Shiba-Rusinov multiplets and clusters of multiorbital adatoms in superconducting substrates: Subgap Green's function approach

TL;DR

This paper provides a comprehensive analysis of Yu-Shiba-Rusinov states in multiorbital impurity clusters on superconductors, using an exact Green's function approach to explore their spectral properties and interactions.

Contribution

It introduces an exact calculation method for subgap states considering multiorbital effects and derives an effective Hamiltonian for impurity hybridization in superconducting substrates.

Findings

Identifies the spectral features of YSR states in multiorbital impurity clusters.

Derives an effective Hamiltonian for impurity interactions mediated by the superconductor.

Analyzes the impact of impurity orientation and frustration on subgap spectra.

Abstract

We discuss all the characteristics of Yu-Shiba-Rusinov states for clusters of impurities with classical magnetic moments in a superconducting substrate with s-wave symmetry. We consider the effect of the multiorbital structure of the impurities and the effect of the crystal field splitting. We solve the problem exactly and calculate the subgap Green's function, which has poles at the energies of the Shiba states and defines the local density of states associated to their wave functions. For the case of impurities sufficiently separated, we derive an effective Hamiltonian to describe the hybridization mediated by the substrate. We analyze the main features of the spectrum and the spectral density of the subgap excitations for impurities in dimer configurations with different relative orientations of the magnetic moments. We also illustrate how the same formalism applies for the solution of a trimer with frustration in the orientation of the magnetic moments.