Dynamics and transport properties of Kondo insulators

TL;DR

This paper develops a non-perturbative local moment approach within dynamical mean-field theory to analyze the dynamics and transport properties of paramagnetic Kondo insulators, revealing universal scaling and connecting theory with experiments.

Contribution

It introduces a new theoretical framework for Kondo insulators that captures universal scaling and matches experimental transport and optical data.

Findings

Universal low-energy scale behavior identified.

Good quantitative agreement with experimental data.

Distinct features of optical gap and temperature effects clarified.

Abstract

A many-body theory of paramagnetic Kondo insulators is described, focusing specifically on single-particle dynamics, scattering rates, d.c. transport and optical conductivities. This is achieved by development of a non-perturbative local moment approach to the symmetric periodic Anderson model within the framework of dynamical mean-field theory. Our natural focus is the strong coupling, Kondo lattice regime; in particular the resultant `universal' scaling behaviour in terms of the single, exponentially small low-energy scale characteristic of the problem. Dynamics/transport on all relevant ($\omega, T$) scales are considered, from the gapped/activated behaviour characteristic of the low-temperature insulator through to explicit connection to single-impurity physics at high $\omega$ and/or $T$; and for optical conductivities emphasis is given to the nature of the optical gap, the temperature scale responsible for its destruction, and the consequent clear distinction between indirect and direct gap scales. Using scaling, explicit comparison is also made to experimental results for d.c. transport and optical conductivites of Ce_3Bi_4Pt_3, SmB_6 and YbB_{12}. Good agreement is found, even quantitatively; and a mutually consistent picture of transport and optics results.