Electron and hole transmission through superconductor - normal metal interfaces

TL;DR

This study measures electron and hole transmission at superconductor-normal metal interfaces, revealing high transmission coefficients (~80%) with negligible barriers, using Andreev-reflection spectroscopy and modified BTK theory.

Contribution

It provides detailed transmission measurements across various normal metals, showing consistent high transmission and minimal barriers, advancing understanding of interface properties in superconductor-normal metal contacts.

Findings

Transmission coefficients around 80% across different metals

Interfaces exhibit negligible dielectric tunneling barriers

Fermi surface mismatch does not significantly affect transmission

Abstract

We have investigated the transmission of electrons and holes through interfaces between superconducting aluminum (Tc = 1.2 K) and various normal non-magnetic metals (copper, gold, palladium, platinum, and silver) using Andreev-reflection spectroscopy at T = 0.1 K. We analyzed the point contacts with the modified BTK theory that includes Dynes' lifetime as a fitting parameter G in addition to superconducting energy gap 2D and normal reflection described by Z. For contact areas from 1 nm^2 to 10000 nm^2 the BTK Z parameter was 0.5, corresponding to transmission coefficients of about 80 %, independent of the normal metal. The very small variation of Z indicates that the interfaces have a negligible dielectric tunneling barrier. Fermi surface mismatch does not account for the observed transmission coefficient.