Resistivity saturation in Kondo insulators

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 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.

Prototypical many-body signatures in transport properties of semiconductors

“…In this scenario, possible impurity states influence transport solely by limiting the lifetime of intrinsic carriers through scattering, not by providing additional carriers. Our findings establish a new phenomenology for transport properties in semiconductors: Below a temperature T * ρ , ρ saturates [22] instead of growing exponentially (see the Boltzmann result (dashed line) in Fig. 1).…”

“…This residual conductivity is at the heart of the resistivity saturation in (non-topological) Kondo insulators and has been discussed in detail in Ref. 22. Similarly, the Hall conductivity in Eq.…”

“…Charge transport. One of the main observations is that in the zero temperature limit T → 0 the electrical (σ) [22] and Hall conductivity (σ B ) remain finite in the presence of residual scattering (Γ > 0). In Eqs.…”

“…Here, our theory provides a complementary microscopic origin for the appearance of the chemical potential-driven characteristic temperature scales T µ ν and T µ ∆ . Note that for particle-hole symmetric systems, where the chemical potential is temperature independent, no such crossover exists and there is only one activation-like regime [22].…”

“…1. For instance, other marcasite compounds (FeAs 2 , RuSb 2 [17,[23][24][25], CrSb 2 [26]), silicides (FeSi [27][28][29], RuSi [30][31][32]), Heusler systems (e.g., Fe 2 VAl [33][34][35][36][37]), other intermetallic compounds [38] (e.g., FeGa 3 , RuGa 3 [18,39,40]), as well as Kondo insulators (e.g., Ce 3 Bi 4 Pt 3 [22,[41][42][43][44][45][46])-strongly suggesting that our scenario based on carriers with finite lifetimes is prototypical for a wide array of different systems.…”