Anatomy of point-contact Andreev reflection spectroscopy from the experimental point of view (review)

TL;DR

This review discusses the principles, models, and challenges of point-contact Andreev-reflection spectroscopy in studying elemental and complex superconductors, highlighting unresolved issues in the method.

Contribution

It provides a comprehensive overview of the experimental aspects, theoretical models, and open problems in point-contact Andreev-reflection spectroscopy for superconductors.

Findings

Theoretical models need refinement for complex superconductors.

Certain aspects of the spectroscopy method remain unresolved.

Application to elemental superconductors is well-understood but challenging for complex cases.

Abstract

We review application of point-contact Andreev-reflection spectroscopy to study elemental superconductors, where theoretical conditions for the smallness of the point-contact size with respect to the characteristic lengths in the superconductor can be satisfied. We discuss existing theoretical models and identify new issues that have to be solved, especially when applying this method to investigate more complex superconductors. We will also demonstrate that some aspects of point-contact Andreev-reflection spectroscopy still need to be addressed even when investigating ordinary metals.