A systematic scanning tunnelling spectroscopy study was made of high-quality thin films. Electron microscopy images and STM topography, together with the scanning tunnelling spectroscopy investigation, permitted a direct correlation to be found between the tunnelling direction and the observed tunnelling spectra, thus confirming that the 2-gap state was intrinsic to MgB2.

STM Tunnelling Spectroscopy in MgB2 Thin Films - the Role of Band Structure in Tunnelling Spectra. M.Iavarone, G.Karapetrov, A.E.Koshelev, W.K.Kwok, G.W.Crabtree, W.N.Kang, E.M.Choi, H.J.Kim, S.I.Lee: Superconductor Science and Technology, 2004, 17, S106-11