Resistivity saturation in Kondo insulators

TL;DR

This paper proposes a new explanation for resistivity saturation in Kondo insulators, attributing it to finite carrier lifetimes and quantum effects rather than surface states, supported by simulations and analysis of experimental data.

Contribution

It introduces an alternative mechanism for resistivity saturation in Kondo insulators, emphasizing the role of scattering rates and quantum regimes over surface conduction.

Findings

Resistivity saturation arises from finite carrier lifetimes and quantum effects.

The mechanism explains the behavior of Ce$_3$Bi$_4$Pt$_3$ under pressure and disorder.

It accounts for the bulk conductivity of SmB$_6$ in narrow-gap semiconductors.

Abstract

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 semiclassical Boltzmann picture. Finite lifetimes of intrinsic carriers limit conduction, impose the existence of a crossover $T^*$, and control - now on par with the gap - the quantum regime emerging below it. We showcase the mechanism with realistic many-body simulations and elucidate how the saturation regime of the Kondo insulator Ce$_3$Bi$_4$Pt$_3$, for which residual conduction is a bulk property, evolves under external pressure and varying disorder. Using a phenomenological formula we derived for the quantum regime, we also unriddle the ill-understood bulk conductivity of SmB$_6$ - demonstrating that our mechanism is widely applicable to correlated narrow-gap semiconductors.