Correlation between bulk thermodynamic measurements and the low-temperature-resistance plateau in SmB₆

Topological insulators are materials characterized by dissipationless, spin-polarized surface states resulting from nontrivial band topologies. Recent theoretical models and experiments suggest that SmB₆ is the first topological Kondo insulator, in which the topologically nontrivial 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 the low-temperature resistance of SmB₆.