Low-temperature conducting state in two candidate topological Kondo insulators:SmB6andCe3Bi4Pt3

Abstract

The authors have studied SmB${}_{6}$ and Ce${}_{3}$Bi${}_{4}$Pt${}_{3}$. Both of these Kondo insulators show a saturation of the increasing resistivity at low temperature that suggests an additional conduction channel and is consistent with the theoretical prediction that these systems should host robust surface states due to their nontrivial topology. While previous work has shown that the resistance saturation in SmB${}_{6}$ is due to conducting surface states, this work demonstrates that the origin of the resistance saturation in Ce${}_{3}$Bi${}_{4}$Pt${}_{3}$ is through the bulk of the material and not the surface. The contrasting behavior of the two materials when the surface is disordered with ion-irradiation supports this conclusion, and also demonstrates the sensitivity of the resistance of the surface state in SmB${}_{6}$ to small levels of disorder. Finally, the low-temperature specific heat of SmB${}_{6}$ shows a residual linear term, and the origin of this term has been highly debated recently. Through measurements of single crystals and powders, it is shown that this term dominantly arises from the bulk and not the surface state.