Resistivity saturation in Kondo insulators

Kondo insulators exhibit a characteristic low-temperature saturation in resistivity the reasons for which have so far eluded physical explanation. Here, using many-body simulations the authors propose an alternative mechanism where the finite lifetimes of the intrinsic bulk carriers play an integral role. Resistivities of heavy-fermion insulators typically saturate below a characteristic temperature T*. For some, metallic surface states, potentially from a non-trivial bulk topology, are a likely source of residual conduction. Here, we establish an alternative mechanism: at low temperature, in addition to the charge gap, the scattering rate turns into a relevant energy scale, invalidating the semi-classical Boltzmann picture. Then, finite lifetimes of intrinsic carriers drive residual conduction, impose the existence of a crossover T*, and control-now on par with the gap-the quantum regime emerging below it. Assisted by realistic many-body simulations, we showcase the mechanism for the Kondo insulator Ce3Bi4Pt3, for which residual conduction is a bulk property, and elucidate how its saturation regime evolves under external pressure and varying disorder. Deriving a phenomenological formula for the quantum regime, we also unriddle the ill-understood bulk conductivity of SmB6-demonstrating a wide applicability of our mechanism in correlated narrow-gap semiconductors.

Automated summary

Kondo insulators exhibit characteristic low-temperature saturation in resistivity, potentially due to the finite lifetimes of intrinsic bulk carriers. Metallic surface states may serve as a likely source of residual conduction. At low temperature, in addition to the charge gap, the scattering rate becomes a relevant energy scale, leading to invalidation of the semi-classical Boltzmann picture.