Scanning tunneling spectroscopy imaging studies were made of the vortex lattice in monocrystalline MgB2. By tunneling parallel to the c-axis, a single superconducting gap (2.2meV) associated with the π band was observed. The vortices in the π band had a large core size as compared with estimates based upon HC2 and exhibited an absence of localized states in the core. Furthermore, superconductivity between the vortices was rapidly suppressed by an applied field. These results suggested that superconductivity in the π band was at least partially induced by the intrinsically superconducting σ band.

Vortex Imaging in the Pi Band of Magnesium Diboride. M.R.Eskildsen, M.Kugler, S.Tanaka, J.Jun, S.M.Kazakov, J.Karpinski, O.Fischer: Physical Review Letters, 2002, 89[18], 187003 (3pp)