Experimental observation of bias-dependent non-local Andreev reflection

TL;DR

This study experimentally demonstrates how non-local Andreev reflection and elastic cotunneling in superconductor-normal metal structures depend on bias energy, with implications for quantum entangler devices.

Contribution

It provides the first clear experimental evidence of bias-dependent non-local Andreev reflection and elastic cotunneling, highlighting the role of the Thouless energy.

Findings

Non-local Andreev reflection occurs at higher energies.

Elastic cotunneling dominates at low energies.

The crossover energy matches the superconductor's Thouless energy.

Abstract

We investigate transport through hybrid structures consisting of two normal metal leads connected via tunnel barriers to one common superconducting electrode. We find clear evidence for the occurrence of non-local Andreev reflection and elastic cotunneling through superconductor when the separation of the tunnel barrier is comparable to the superconducting coherence length. The probability of the two processes is energy dependent, with elastic cotunneling dominating at low energy and non-local Andreev reflection at higher energies. The energy scale of the crossover is found to be the Thouless energy of the superconductor, which indicates the phase coherence of the processes. Our results are relevant for the realization of recently proposed entangler devices.