From Cooper pair splitting to the non-local spectroscopy of a Shiba state

TL;DR

This paper investigates how non-local conductance correlations in a quantum dot-superconductor system can arise from both Cooper pair splitting and the probing of Shiba states, clarifying their interplay through experiments and modeling.

Contribution

It provides a detailed experimental and theoretical analysis distinguishing between Cooper pair splitting and Shiba state effects in non-local conductance correlations.

Findings

Correlation strength varies with tunnel barrier tuning.

Model fitting yields device tunnel couplings.

CPS contribution to non-local signals quantified.

Abstract

Cooper pair splitting (CPS) is a way to create spatially separated, entangled electron pairs. To this day, CPS is often identified in experiments as a spatial current correlation. However, such correlations can arise even in the absence of CPS, when a quantum dot is strongly coupled to the superconductor, and a subgap Shiba state is formed. Here, we present a detailed experimental characterization of those spatial current correlations, as the tunnel barrier strength between the quantum dot and the neighboring normal electrode is tuned. The correlation of the non-local signal and the barrier strength reveals a competition between CPS and the non-local probing of the Shiba state. We describe our experiment with a simple transport model, and obtain the tunnel couplings of our device by fitting the model's prediction to the measured conductance correlation curve. Furthermore, we use our theory to extract the contribution of CPS to the non-local signal.