Energy gap substructures in conductance measurements of MgB<inf>2</inf>-based Josephson junctions: beyond the two-gap model

Abstract

© 2015 IOP Publishing Ltd Several theoretical analyses of the two superconducting energy gaps of magnesium diboride,Δπ and Δσ, predict substructures within each energy gap. We report additional experimental evidence for these features, in tunneling conductance data using multiple samples measured at very low temperatures. The absence of these features in c-axis tunneling, and a sharp peak in the subgap (associated with the counterelectrode material), support the conclusion that these features are intrinsic to MgB2. By demonstrating the inadequacy of a simple two-gap model in fitting the data, we illustrate that distinctions between theoretical models of energy gap substructures are experimentally accessible.