  We use scanning tunneling microscopy to investigate the (001) surface of
cleaved SmB6 Kondo insulator. Variable temperature dI/dV spectroscopy up to 60
K reveals a gap-like density of state suppression around the Fermi level, which
is due to the hybridization between the itinerant Sm 5d band and localized Sm
4f band. At temperatures below 40 K, a sharp coherence peak emerges within the
hybridization gap near the lower gap edge. We propose that the in-gap resonance
state is due to a collective excitation in magnetic origin with the presence of
spin-orbital coupling and mixed valence fluctuations. These results shed new
lights on the electronic structure evolution and transport anomaly in SmB6.
