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*=17K , 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 .