  We perform a detailed experimental study of the band excitations and
tunneling properties of ultracold fermions in optical lattices. Employing a
novel multi-band spectroscopy for fermionic atoms we can measure the full band
structure and tunneling energy with high accuracy. In an attractive Bose-Fermi
mixture we observe a significant reduction of the fermionic tunneling energy,
which depends on the relative atom numbers. We attribute this to an
interaction-induced increase of the lattice depth due to self-trapping of the
atoms.
