Characterization of off-axis MgB2 epitaxial thin films for planar junctions

Using scanning tunneling spectroscopy, we perform a full mapping of the quasiparticle density of states of magnesium diboride (MgB2) epitaxial thin films grown on (110) yttrium stabilized zirconia (YSZ) by hybrid physical-chemical vapor deposition. The films have critical temperatures of 40 K. X-ray measurements show an epitaxial MgB2 growth having the c-axis tilted by 32 degrees with respect to the normal to the substrate, consistent with the atomic force microscopy images of the sample. Scanning tunneling spectroscopy clearly finds that the spectroscopic peak associated to the pi gap is reduced on most of the film surface and the feature representative of the sigma gap is present, with different intensity, on the majority of the sample's surface, which is consistent with x-ray measurements.