Temperature and field dependence of MgB2 energy gaps from tunneling spectra

TL;DR

This study investigates the temperature and magnetic field effects on the superconducting energy gaps of MgB2 using tunneling spectra, revealing evidence for multiple gaps and their behavior under varying conditions.

Contribution

The paper provides the first detailed analysis of MgB2's multiple energy gaps and their dependence on temperature and magnetic field through tunneling spectroscopy.

Findings

Identification of a small energy gap around 2 meV

Evidence for a larger gap approximately 4.5 times the smaller one

Superconducting junction stability up to 3.2 Tesla

Abstract

We have synthesized MgB2/Pb planar junctions to study the temperature and field dependence of the superconducting energy gap of MgB2. The major peak occurs at Delta of about 2 meV, and this corresponds to a 2Delta/kBTc value of 1.18. While this is significantly smaller than the BCS weak coupling value, there are features in the tunneling spectra indicating the possibility of another larger gap. By fitting the dI/dV curves with a simple model, the larger gap is estimated to be about 4.5 times the smaller gap. The study of the effect of magnetic field on the junctions shows a stability only up to a field of 3.2T then junctions "collapsed" into Josephson tunneling for higher fields. Estimation of the major energy gap from Josephson tunneling is consistent with that from quasiparticle tunneling.