Temperature Dependence of Superconducting Gaps in Mg(Al)B2 System Investigated by SnS-Andreev Spectroscopy

TL;DR

This study uses SnS-Andreev spectroscopy to analyze the temperature dependence of superconducting gaps in Mg(Al)B2, revealing deviations from BCS behavior due to interband effects and confirming theoretical models.

Contribution

First direct measurement of superconducting gap temperature dependence in Mg(Al)B2 showing deviations from BCS theory and agreement with theoretical predictions.

Findings

Deviations from standard BCS behavior due to k-space proximity effect.

Qualitative agreement with theoretical models of interband coupling.

Effective analysis of samples with structural defects and Tc variations.

Abstract

Detailed temperature dependence of both superconducting gaps was obtained directly by means of SnS-Andreev spectroscopy. The \Delta \sigma,\pi(T) -curves were shown to be deviated from standard BCS-like behavior, due to k-space proximity effect between \sigma - and \pi - condensates, which could give a key to experimental determination of interband electron-phonon coupling constants. For the first time, an excellent qualitative agreement with theoretical predictions of Nicol and Carbotte, and Moskalenko and Suhl was shown. dI(V)/dV-spectra of SnS-Andreev contacts based on MgB2 samples (with defects of crystal structure), and Mg(Al)B2 polycrystalline samples (with the local critical temperatures Tc variation 10 K < Tc < 37 K) were studied by means of the "break-junction" technique within the temperature range 4.2 K < T < Tc.