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

Abstract

Crossed Andreev reflection (CAR) in metallic nanostructures, a possible basis forsolid-state electron entangler devices, is usually investigated by detecting non-local voltagesin multi-terminal superconductor/normal metal devices. This task is difficult because othersubgap processes may mask the effects of CAR. One of these processes is the generation ofcharge imbalance (CI) and the diffusion of non-equilibrium quasi-particles in thesuperconductor. Here we demonstrate a characteristic dependence of non-local CIon a magnetic field applied parallel to the superconducting wire, which can beunderstood by a generalization of the standard description of CI to non-localexperiments. These results can be used to distinguish CAR and CI and to extract CIrelaxation times in superconducting nanostructures. In addition, we investigatethe dependence of non-local CI on the resistance of the injector and detectorcontacts and demonstrate a quantitative agreement with a recent theory using onlymaterial and junction characteristics extracted from separate direct measurements.