MgB2 Energy Gap Determination by Scanning Tunneling Spectroscopy
  We report scanning tunneling spectroscopy (STS) measurements of the gap properties of both ceramic MgB2 and c-axis oriented epitaxial MgB2 thin films. Both show a temperature dependent zero bias conductance peak and evidence for two superconducting gaps. We report tunneling spectroscopy of superconductor-insulator-superconductor (S-I-S) junctions formed in two ways in addition to normal metal-insulator-superconductor (N-I-S) junctions. We find a gap delta=2.3-2.8 meV, with spectral features and temperature dependence that are consistent between S-I-S junction types. In addition, we observe evidence of a second, larger gap, delta=7.2 meV, consistent with a proposed two-band model. 
T.W. Heitmann, S.D. Bu, D.M. Kim, J.H. Choi, J. Giencke, C.B. Eom,   K.A. Regan, N. Rogado, M.A. Hayward, T. He, J.S. Slusky...