Proximity-induced Shiba states in a molecular junction

TL;DR

This study demonstrates the creation and control of Yu-Shiba-Rusinov states in a molecular junction with a magnetic radical, revealing how paramagnetic impurities interact with proximity-induced superconductivity.

Contribution

It introduces a novel experimental platform integrating a stable organic radical into superconductor junctions to study Shiba states with tunable coupling.

Findings

Observation of spin-induced Shiba states in a molecular junction.

Ability to access both singlet and doublet ground states.

Shiba states mediated by electron-hole pairs instead of Cooper pairs.

Abstract

Superconductors containing magnetic impurities exhibit intriguing phenomena derived from the competition between Cooper pairing and Kondo screening. At the heart of this competition are the Yu-Shiba-Rusinov (Shiba) states which arise from the pair breaking effects a magnetic impurity has on a superconducting host. Hybrid superconductor-molecular junctions offer unique access to these states but the added complexity in fabricating such devices has kept their exploration to a minimum. Here, we report on the successful integration of a model spin 1/2 impurity, in the form of a neutral and stable all organic radical molecule, in proximity-induced superconducting break-junctions. Our measurements reveal excitations which are characteristic of a spin-induced Shiba state due to the radical's unpaired spin strongly coupled to a superconductor. By virtue of a variable molecule-electrode coupling, we access both the singlet and doublet ground states of the hybrid system which give rise to the doublet and singlet Shiba excited states, respectively. Our results show that Shiba states are a robust feature of the interaction between a paramagnetic impurity and a proximity-induced superconductor where the excited state is mediated by correlated electron-hole (Andreev) pairs instead of Cooper pairs.