Spatial variations of the superconductor gap structure in MgB2/Al composite

Abstract

Composites consisting of MgB2 and Al, 11% by volume, undergo a transition to superconductivity onset at TC = 38 K, close to the value reported for pure MgB2. The transition appears to have broadened, as determined by both magnetic and transport measurements, possible due to the proximity effect and disorder. Spatially resolved tunneling spectroscopy at 4.2 K exhibit a distribution of gap structures, from BCS-like spectra with 2D/kBTc = 3.2 to spectra that are typical for proximity superconductors.