Tuning Yu-Shiba-Rusinov States in a Quantum Dot

TL;DR

This paper investigates sub-gap states in an InAs nanowire quantum dot coupled to superconducting and normal leads, using transport spectroscopy and numerical renormalization group theory to understand their behavior under tuning parameters.

Contribution

It provides a detailed experimental and theoretical analysis of Yu-Shiba-Rusinov states in a quantum dot system, including parameter extraction and intuitive descriptions.

Findings

Resolved sub-gap states tracked with tuning parameters

System parameters extracted via numerical renormalization group fits

Observation of quantum phase transition in the system

Abstract

We present transport spectroscopy of sub-gap states in a bottom gated InAs nanowire coupled to a normal lead and a superconducting aluminium lead. The device shows clearly resolved sub-gap states which we can track as the coupling parameters of the system are tuned and as the gap is closed by means of a magnetic field. We systematically extract system parameters by using numerical renormalization group theory fits as a level of the quantum dot is tuned through a quantum phase transition electrostatically and magnetically. We also give an intuitive description of sub-gap excitations.