Conductance features in point contact Andreev reflection spectra

Abstract

Point contact Andreev reflection (PCAR) spectroscopy is a common technique fordetermining the spin polarization of a ferromagnetic sample. The polarization is extractedby measuring the bias dependence of the conductance of a metallic/superconducting pointcontact. Under ideal conditions, the conductance is dominated by Andreev reflection andthe Blonder–Tinkham–Klapwijk (BTK) model can be used to extract a value for thepolarization. However, PCAR spectra often exhibit unwanted features in theconductance that cannot be appropriately modelled with the BTK theory. Inthis paper we isolate some of these unwanted features and show that any furtherextraction of the spin polarization from these non-ideal spectra proves unreliable.Understanding the origin of these features provides an objective criterion forrejection of PCAR spectra unsuitable for fitting with the modified BTK model.