Local and non-local two-electron tunneling processes in a Cooper pair splitter

TL;DR

This paper experimentally investigates local and non-local two-electron tunneling processes in a Cooper pair splitter, revealing significant differences in coupling strengths and providing theoretical explanations for these phenomena.

Contribution

It provides the first detailed measurement of tunneling rates and coupling coefficients for various Andreev and cotunneling processes in a Cooper pair splitter.

Findings

Non-local Andreev and elastic cotunneling have similar coupling coefficients.

Local Andreev process is over two orders of magnitude stronger than non-local.

Theory explains the difference based on electron diffusion and junction transparency.

Abstract

We measure the tunneling rates and coupling coefficients for local Andreev, non-local Andreev and elastic cotunneling processes. The non-local Andreev process, giving rise to Cooper pair splitting, exhibits the same coupling coefficient as the elastic co-tunneling whereas the local Andreev process is more than two orders of magnitude stronger than the corresponding non-local one. Theory estimates describe the findings and explain the large difference in the non-local and local coupling arising from competition between electron diffusion in the superconductor and tunnel junction transparency.