Scanning tunneling microscopic measurements were made of the surface of MgB2 having a critical temperature of 39K. In a zero magnetic field, the conductance spectra could be analyzed in terms of standard BCS theory, with a smearing parameter. The value of the superconducting gap was 5meV at 4.2K, with no experimentally significant variation across the surface of the sample. The temperature dependence of the gap was of BCS form, fully consistent with phonon-mediated superconductivity. The application of a magnetic field induced strong pair-breaking as seen in the conductance spectra at fields of up to 6T.

Scanning Tunneling Spectroscopy in MgB2. G.Karapetrov, M.Iavarone, W.K.Kwok, G.W.Crabtree, D.G.Hinks: Physical Review Letters, 2001, 86[19], 4374-7