Low-temperature conducting state in two candidate topological Kondo insulators: SmB6 and Ce3Bi4Pt3

We have investigated the low-temperature conducting state of two Kondo insulators, SmB6 and Ce3Bi4Pt3, which have been theoretically predicted to host topological surface states. Through comparison of the specific heat of as-grown and powdered single crystals of SmB6, we show that the residual term that is linear in temperature is not dominated by any surface state contribution, but rather is a bulk property. In Ce3Bi4Pt3, we find that the Hall coefficient is independent of sample thickness, which indicates that conduction at low temperatures is dominated by the bulk of the sample, and not by a surface state. The low-temperature resistivity of Ce3Bi4Pt3 is found to monotonically decrease with low concentrations of disorder introduced through ion irradiation. This is in contrast to SmB6, which is again indicative of the contrasting origins of the low-temperature conduction. In SmB6, we also show that the effect of low concentrations of irradiation damage of the surface with Fe+ ions is qualitatively consistent with damage with nonmagnetic ions.