Self-energy Effect of Superconducting Energy Gap in Point-Contact Spectra of MgB$_2$

TL;DR

This paper investigates how self-energy effects influence the superconducting energy gap features in point-contact spectra of MgB₂, providing theoretical expressions that match experimental observations.

Contribution

It derives asymptotic expressions for phonon structures in MgB₂'s point-contact spectra, accounting for self-energy effects in different contact regimes.

Findings

Expressions match experimental spectra of MgB₂'s π-band

Self-energy effects significantly influence spectral features

Theoretical results are semi-quantitatively consistent with measurements

Abstract

In strong-coupling superconductors with a short electron mean free path the self-energy effects in the superconducting order parameter play a major role in the phonon manifestation of the point-contact spectra at the above-gap energies. We derive asymptotic expressions of the phonon structure in MgB$%_{2}$ in the case $eV\gg\Delta $ for tunnel, ballistic, and diffusive point-contacts and show that these expressions not only qualitatively, but also semi-quantitatively correspond to the measurements of the phonon structure in the point-contact spectra for the $\pi$-band of MgB$_{2}$ c-axis oriented thin films.