Resistivity saturation in Kondo insulators

Resistivities of heavy-fermion insulators typically saturate below a characteristic temperature $T^*$. For some, metallic surface states, potentially from non-trivial bulk topology, are likely source residual conduction. Here, we establish an alternative mechanism: At low temperature, in addition to the charge gap, scattering rate turns into relevant energy scale, invalidating semiclassical Boltzmann picture. Finite lifetimes intrinsic carriers limit conduction, impose existence crossover $T^*$, and control - now on par with gap quantum regime emerging it. We showcase mechanism realistic many-body simulations elucidate how saturation Kondo insulator Ce$_3$Bi$_4$Pt$_3$, for which conduction is property, evolves under external pressure varying disorder. Using phenomenological formula derived regime, also unriddle ill-understood conductivity SmB$_6$ demonstrating that our widely applicable correlated narrow-gap semiconductors.