Effect of transport-induced charge inhomogeneity on point-contact Andreev reflection spectra at ferromagnet-superconductor interfaces

TL;DR

This paper models how charge inhomogeneity at ferromagnet-superconductor interfaces affects point-contact Andreev reflection spectra, explaining anomalous features observed experimentally.

Contribution

It introduces a modified 3D BTK formalism considering charge inhomogeneity via evanescent modes, revealing its impact on conductance spectra.

Findings

Charge inhomogeneity causes dip structures and zero-bias conductance peaks.

Transport mechanisms like evanescent Andreev reflection are key to spectral features.

Charge effects can explain anomalous PCAR spectra characteristics.

Abstract

We investigate the transport properties of a ferromagnet-superconductor interface within the framework of a modified three-dimensional Blonder-Tinkham-Klapwijk formalism. In particular, we propose that charge inhomogeneity forms via two unique transport mechanisms, namely, evanescent Andreev reflection and evanescent quasiparticle transmission. Furthermore, we take into account the influence of charge inhomogeneity on the interfacial barrier potential and calculate the conductance as a function of bias voltage. Point-contact Andreev reflection (PCAR) spectra often show dip structures, large zero-bias conductance enhancement, and additional zero-bias conductance peak. Our results indicate that transport-induced charge inhomogeneity could be a source of all these anomalous characteristics of the PCAR spectra.