We report on the results of scanning tunneling spectroscopy measurements on single crystals of MgB2. Tunneling was performed both parallel and perpendicular to the crystalline c-axis. In the first case, a Single superconducting gap (△π= 2.2 meV) associated with the π-band is observed. Tunneling parallel to the ab-plane reveals an additional, larger gap (△ ∂〜7 meV) originating in the highly two -dimensional ∂- band. Vortex imaging in the π -band was performed with the field and tunnel current parallel to the c-axis. The vortices have a large core size compared to estimates based on Hc2, and show an absence of localized states in the core. Furthermore, superconductivity between the vortices is rapidly suppressed by an applied field. A comparison to specific heat measurements is performed.

Keywords MgB2, STS, vortex