Contact resistance dependence of crossed Andreev reflection

TL;DR

This study experimentally investigates how contact resistance influences crossed Andreev reflection in superconductor/normal metal devices, revealing conditions where CAR dominates and highlighting its potential for solid-state entanglement.

Contribution

It demonstrates the dependence of crossed Andreev reflection dominance on contact resistance in hybrid devices, providing insights for controlling CAR in quantum applications.

Findings

CAR can dominate nonlocal transport at specific contact resistances

Higher contact resistances weaken CAR relative to elastic cotunneling

Systematic change in nonlocal resistance with contact resistance variations

Abstract

We show experimentally that in nanometer scaled superconductor/normal metal hybrid devices and in a small window of contact resistances, crossed Andreev reflection (CAR) can dominate the nonlocal transport for all energies below the superconducting gap. Besides CAR, elastic cotunneling (EC) and nonlocal charge imbalance (CI) can be identified as competing subgap transport mechanisms in temperature dependent four-terminal nonlocal measurements. We demonstrate a systematic change of the nonlocal resistance vs. bias characteristics with increasing contact resistances, which can be varied in the fabrication process. For samples with higher contact resistances, CAR is weakened relative to EC in the midgap regime, possibly due to dynamical Coulomb blockade. Gaining control of CAR is an important step towards the realization of a solid state entangler.