A study was made of the structure of the superconducting gap in thin films by means of point-contact spectroscopy using a Au tip. The films were produced by depositing pure B onto a sapphire substrate, using e-beam evaporation, followed by reaction with Mg vapour. The films had a TC of 38.6K and resistivity of about 20μΩcm at 40K. The point-contact spectra prove directly the existence of a multi-valued order parameter in MgB2, with 2 distinct values of the gap, Δ1 = 2.3meV and Δ2 = 6.2meV at 4.2K. Analysis of the spectra in terms of the Blonder–Tinkham–Klapwijk model revealed that both gaps close simultaneously at the TC of the film.

Structure of the Superconducting Gap in MgB2 from Point-Contact Spectroscopy. Y.Bugoslavsky, Y.Miyoshi, G.K.Perkins, A.V.Berenov, Z.Lockman, J.L.MacManus-Driscoll, L.F.Cohen, A.D.Caplin, H.Y.Zhai, M.P.Paranthaman, H.M.Christen, M.Blamire: Superconductor Science and Technology, 2002, 15, 526-32