Break-junction technique in application to layered superconductors (Review article)

TL;DR

This review discusses the application of the break-junction technique to layered superconductors, enabling detailed spectroscopic analysis of superconducting gaps, electron-boson interactions, and phonon modes in various high-temperature superconductors.

Contribution

It provides a comprehensive overview of how the break-junction method can be used to study superconducting properties and gap anisotropy in layered superconductors, highlighting its advantages and challenges.

Findings

Determination of superconducting gap values and temperature dependence.

Estimation of gap anisotropy and electron-boson coupling constants.

High-resolution investigation of optical phonon modes.

Abstract

Here presented a systematic study of superconductor-constriction-superconductor contacts realized by a break-junction technique in layered superconductors. Depending on the constriction transparency the tunneling and SnS-Andreev spectroscopies could be used, for the direct determination of values of superconducting gaps, characteristic BCS-ratios and gap temperature dependences in cuprate superconductors, magnesium diboride, novel pnictides and chalcogenides. Basing on these data, one can estimate the gap anisotropy magnitude as well as values of electron-boson coupling constants. We discuss the advantages and difficulties of the break-junction technique and demonstrate this method is powerful enough for high-resolution investigation of optical phonon modes in high-temperature superconducting cuprates and for creating of the contacts with the selective transparence in Mg$_{1-x}$Al$_x$B$_2$ compounds.