  Topological insulators are materials characterized by dissipationless,
spin-polarized surface states resulting from non-trivial band topologies.
Recent theoretical models and experiments suggest that SmB6 is the first
topological Kondo insulator, in which the topologically non-trivial band
structure results from electron-electron interactions via Kondo hybridization.
Here, we report that the surface conductivity of SmB6 increases systematically
with bulk carbon content. Further, addition of carbon is linked to an increase
in n-type carriers, larger low temperature electronic contributions to the
specific heat with a characteristic temperature scale of T* = 17 K, and a
broadening of the crossover to the insulating state. Additionally, X-ray
absorption spectroscopy shows a change in Sm valence at the surface. Our
results highlight the importance of phonon dynamics in producing a Kondo
insulating state and demonstrate a correlation between the bulk thermodynamic
state and low temperature resistance of SmB6.
