Magnetic field and contact resistance dependence of non-local charge imbalance

TL;DR

This paper investigates how magnetic fields and contact resistance affect non-local charge imbalance in superconductor/normal metal devices, providing methods to distinguish it from crossed Andreev reflection and extract relaxation times.

Contribution

It demonstrates the magnetic field dependence of non-local charge imbalance and its relation to contact resistance, offering a way to differentiate it from crossed Andreev reflection.

Findings

Charge imbalance depends on magnetic field orientation and strength.

Contact resistance influences the magnitude of non-local charge imbalance.

Results agree quantitatively with recent theoretical models.

Abstract

Crossed Andreev reflection (CAR) in metallic nanostructures, a possible basis for solid-state electron entangler devices, is usually investigated by detecting non-local voltages in multi-terminal superconductor/normal metal devices. This task is difficult because other subgap processes may mask the effects of CAR. One of these processes is the generation of charge imbalance (CI) and the diffusion of non-equilibrium quasi-particles in the superconductor. Here we demonstrate a characteristic dependence of non-local CI on a magnetic field applied parallel to the superconducting wire, which can be understood by a generalization of the standard description of CI to non-local experiments. These results can be used to distinguish CAR and CI and to extract CI relaxation times in superconducting nanostructures. In addition, we investigate the dependence of non-local CI on the resistance of the injector and detector contacts and demonstrate a quantitative agreement with a recent theory using only material and junction characteristics extracted from separate direct measurements.