Non-Local Correlations in Normal Metal-Superconducting Systems

TL;DR

This paper investigates nonlocal effects in normal-metal and superconductor systems, revealing voltages consistent with crossed Andreev reflection and elastic cotunneling, which involve coherent electron correlations.

Contribution

It provides experimental evidence of nonlocal voltages linked to crossed Andreev reflection and elastic cotunneling in Au/Al systems with high interface transparency.

Findings

Nonlocal voltages observed with temperature and spatial dependence.

Voltages match theoretical predictions for crossed Andreev reflection and cotunneling.

Distinct from typical charge imbalance signals.

Abstract

We examine nonlocal effects between normal-metal gold probes connected by superconducting aluminum. For highly transparent Au/Al interfaces, we find nonlocal voltages that obey a spatial and temperature evolution distinct from the nonequilibrium charge imbalance signals usually found in such systems. These voltages are consistent with the predicted effects of crossed Andreev reflection and elastic cotunneling, effects that involve coherent correlations between spatially separated electrons.