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

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.

Nonlocal conductance spectroscopy of Andreev bound states in gate-defined InAs/Al nanowires

“…Using the same transport processes, quantum dots coupled to one superconducting and two normal leads have been used to demonstrate Cooper-pair splitting [10][11][12][13]. Nonlocal spectroscopy of subgap states induced by quantum dot states have been reported in vapor-liquid-solid grown NWs and carbon nanotubes [12,14].…”