The role of critical current on point contact Andreev Reflection spectrum between a normal metal and a superconductor

TL;DR

This paper investigates the unexpected conductance dips in point contact spectra between normal metals and superconductors, attributing them to non-ballistic contact conditions and analyzing their impact on BTK model interpretations.

Contribution

It provides a systematic study linking conductance dips to contact area and non-ballistic effects, highlighting limitations of the standard BTK analysis.

Findings

Dips are caused by non-ballistic contact conditions.

Contact area correlates with the presence of dips.

Standard BTK analysis may introduce errors when dips are present.

Abstract

The point contact spectrum between a normal metal and a superconductor often shows unexpected sharp dips in the conductance at voltage values larger than the superconducting energy gap. These dips are not predicted in the Blonder-Tinkham-Klapwizk (BTK) theory, commonly used to analyse these contacts. We present here a systematic study of these dips in a variety of contacts between different combinations of a superconductor and a normal metal. From the correlation between the characteristics of these dips with the contact area, we can surmise that such dips are caused by the contact not being in the ballistic limit. An analysis of the possible errors introduced while analysing such a spectrum with the standard BTK model is also presented.