Andreev Reflection Spectroscopy in Niobium Point Contacts in Magnetic Field

TL;DR

This paper improves the understanding of Andreev reflection spectroscopy in niobium point contacts under magnetic fields by modifying existing models to account for vortex core contributions, affecting spin polarization measurements.

Contribution

The authors extend the Blonder-Tinkham-Klapwijk model to include vortex core effects, enhancing the interpretation of PCAR experiments in magnetic fields.

Findings

Modified model better fits experimental data in magnetic fields.

Stray magnetic fields influence spin polarization measurements.

Potential misinterpretation of spin polarization due to magnetic effects.

Abstract

The Blonder-Tinkham-Klapwijk model of the Point-Contact Andreev Reflection spectroscopy does not provide an adequate description of experiment in the presence of magnetic field. We demonstrate this using a junction between a niobium tip and a copper film. We modify the the-ory to explicitly take into account the contribution to conductance that stems from the normal vortex cores in the superconductor. These results have important implications for interpretation of transport spin polarisation measurements using PCAR technique. We demonstrate that stray magnetic fields can be responsible for the experimentally observed dependence of the spin po-larisation on the strength of the interface barrier, and potential misassignment of the inferred spin polarisation.