  Topological Kondo insulator SmB6 has attracted quite a lot of attentions from
condensed matter physics community. A number of unique electronic properties,
including low- temperature resistivity anomaly, 1D electronic transport and 2D
Fermi surfaces have been observed in SmB6. Here, we report on thermoelectric
transport properties of polycrystalline SmB6 over a broad temperature from 300
K to 2 K. An anomalous transition in the temperature-dependent Seebeck
coefficient S from S(T) ~ T-1 to S(T) ~ T was observed around 12 K. Such a
transition demonstrates a transition of conductivity from 3D metallic bulk
states to 2D metallic surface states with insulating bulk states. Our results
suggest that the thermotransport measurements could be used for the
characterization of state transition in topological insulators.
