Superconducting energy gap distribution of MgB2 investigated by point-contact spectroscopy

We performed point-contact spectroscopy on the binary superconductor MgB2. The differential conductance shows gap-related structures which vary in wid th and position from contact to contact. The distribution of energy gaps sh ows a distinct accumulation around 1.7 and 7 meV which is associated with t he occurrence of a small and a large energy gap in MgB2. While with increas ing T the structure in dI/dV associated with the small gap is present up to T-c, in magnetic field it is suppressed well below B-c2.