Soft point contact spectroscopy to probe superconductor-normal metal junctions

Abstract

Point contact Andreev Reflection (PCAR) spectroscopy is a powerful tool to study superconductors, in particular the superconducting energy gap and its symmetry. We report on the use of the “soft point contact technique” which has been integrated with a cryogen free platform where its vibrations does not disturb the stability of the contact giving noise free PCAR spectra. We further show for large area, high transparency junctions between normal metals and superconductors, an additional peak is observed in the PCAR spectra at the zero bias referred to as the zero bias conductance (ZBC) anomaly. Through our studies on various superconducting films and various contacts, we associate the ZBC anomaly with the increased influence of the superconducting proximity effect which suppresses the transition temperature (Tc) of the junction.