Point-contact spectroscopy of MgB2

TL;DR

This study uses point-contact spectroscopy to investigate the superconducting gaps in MgB2, confirming the multiband nature with two distinct gaps that behave differently under magnetic fields and reveal phonon-related features.

Contribution

It provides experimental evidence for two superconducting gaps in MgB2 and details their behavior under magnetic fields, supporting the multiband superconductivity model.

Findings

Two gaps close at the same transition temperature.

The smaller gap is suppressed by a low magnetic field.

Reproducible phonon-related non-linearities observed.

Abstract

Point-contact spectroscopy measurements on magnesium diboride reveal the existence of two superconducting energy gaps closing at the same transition temperature in line with the multiband model of superconductivity. The sizes of the two gaps ($\Delta_{\pi}$ = 2.8 meV and $\Delta_{\sigma}$ = 6.5-7 meV) are respectively smaller and larger than the expected weak coupling value of the one-gap superconductor. The smaller gap is rapidly filled by a small magnetic field of about 1-2 Tesla much lower than the real upper critical field $H_{c2}$. The larger gap is closed at the anisotropic $H_{c2}$. Above the gap energies reproducible non-linearities are observed at the characteristic phonon energies of MgB$_2$.