Microscopic Scattering Approach to In-Gap States: Cr Adatoms on Superconducting \beta-Bi2Pd

TL;DR

This paper introduces a detailed microscopic scattering model for Yu-Shiba-Rusinov states caused by Cr adatoms on Pd, combining ab initio calculations with Green's functions to interpret STM data and explore topological impurity chains.

Contribution

It develops a novel microscopic framework integrating ab initio and Green's function methods to accurately describe impurity-induced in-gap states in superconductors.

Findings

Reproduces key STM features of YSR states, including asymmetric peaks and isotropic maps.

Decomposes YSR states revealing contributions from nearly degenerate symmetry representations.

Shows spin-orbit coupling causes partial spin polarization and spatial asymmetry from hybridization.

Abstract

We develop a microscopic scattering formalism to describe Yu-Shiba-Rusinov (YSR) states due to a single Cr adatom on the Bi-terminated surface of $\beta-Bi_2Pd$, by combining ab initio Wannier functions with a real-space Green's function approach in the Bogoliubov-de Gennes formalism. Our framework reproduces key scanning tunneling spectroscopy features, including a single particle-hole asymmetric YSR peak and isotropic dIdV maps around the impurity. Decomposing the YSR states reveals contributions from four nearly degenerate C4v representations, with energy broadening masking their individual signatures. Spin-orbit coupling induces partial spin polarization, while the spatial asymmetry between particle and hole components arises from Cr d-Bi p hybridization. These results highlight the importance of realistic band structures and microscopic modeling for interpreting STM data and provide a foundation for studying impurity chains hosting topological excitations.