  The study of the anisotropic superconductor MgB2 using a combination of
scanning tunneling microscopy and spectroscopy reveals two distinct energy gaps
at Delta1=2.3 meV and Delta2=7.1 meV. Different spectral weights of the partial
superconducting density of states (PDOS) are a reflection of different
tunneling directions in this multi-band system. Our experimental observations
are consistent with the existence of two-band superconductivity in the presence
of interband superconducting pair interaction and quasiparticle scattering.
Temperature evolution of the tunneling spectra follows the BCS scenario with
both gaps vanishing at the bulk Tc. Indeed, the study of tunneling junctions
exhibiting only the small gap (c-axis tunneling) clearly and reproducibly show
that this gap persists up to the bulk Tc. The data confirm the importance of
Fermi-surface sheet dependent superconductivity in MgB2 proposed in the
multigap model by Liu et al.
