A study was made of the anisotropic superconductor by using a combination of scanning electron microscopy and scanning tunnelling spectroscopy. Tunnelling spectroscopy performed on thin films and pellets revealed 2 distinct energy gaps at Δ1 = 2.3meV and Δ2 = 7.1meV. On different crystallites within the polycrystalline sample different spectral weights of the partial densities of states were observed. They reflect different tunnelling directions with respect to the crystallographic orientation of the grain in a multiband system. Indeed when tunnelling in the c-axis films only one superconducting gap was observed, which was associated with the 3D band in this system. Temperature evolution of the tunnelling spectra revealed that both gaps close simultaneously near the bulk critical temperature. The experimental results were consistent with 2-band superconductivity in the presence of strong pair interaction between the 2 bands.

MgB2 - Directional Tunnelling and Two-Band Superconductivity. M.Iavarone, G.Karapetrov, A.Koshelev, W.K.Kwok, D.Hinks, G.W.Crabtree, W.N.Kang, E.M.Choi, H.J.Kim, S.I.Lee: Superconductor Science and Technology, 2003, 16, 156-61