Normal reflection at superconductor - normal metal interfaces due to Fermi surface mismatch

TL;DR

This paper investigates how Fermi surface mismatch causes normal electron reflection at superconductor-normal metal interfaces, using Andreev reflection measurements on Nb and Al contacts, revealing discrepancies with theoretical predictions.

Contribution

It provides experimental evidence linking Fermi surface mismatch to normal reflection at superconductor-normal metal interfaces, highlighting differences from existing theoretical models.

Findings

Distribution of interface barrier strength Z peaks due to Fermi surface mismatch

Reflection coefficients are smaller than theoretical predictions

Results suggest Fermi surface mismatch significantly influences interface reflection

Abstract

Electrons can be reflected at an interface between two metals because of a dielectric barrier or different properties of the Fermi surface. Andreev reflection allows to directly measure normal reflection when one of the metals is a superconductor. We have investigated normal reflection at interfaces between non-magnetic normal metals and superconducting Nb (Tc = 9.2 K) and Al (Tc = 1.2 K). The distribution of the values of the relative strength of the interface barrier, Z, for a number of contacts of a specific metal combination shows a well-defined peak which can be attributed to Fermi surface mismatch. Our reflection coefficients are generally smaller than those predicted theoretically or those derived from proximity-effect studies of normal-superconductor bi-layers.