Fragility of the Kondo insulating gap against disorder: Relevance to recent puzzles in topological Kondo insulators

Sudeshna Sen,Eduardo Miranda,Vladimir Dobrosavljević,Wei Ku,N S Vidhyadhiraja

doi:10.1103/physrevresearch.2.033370

Abstract

Kondo insulators are strongly correlated system in which a clean insulating gap emerges only at very low temperature due to many-body effects involving localized $f$-electrons. However, certain Kondo insulators, like SmB$_6$ and Ce${_3}$Bi${_4}$Pt${_3}$, display metallic behaviors at extremely low temperatures, that have defied current understanding. Recent advances in topological effects in materials has raised the attention on the protected surface states in these "topological Kondo insulators" as a potential resolution to some of the puzzling behaviors. Here we resolve these puzzles via a different route, by showing that the emergent Kondo insulating scale is extremely vulnerable against moderate degree of disorder, such that the gap is filled with a small number of states. Therefore, the real samples are probably never truly insulating and this in turn compromises the essential building block of topological considerations. Our results suggest strongly that systems like the Slater insulators would be a more promising direction to extend the realm of topology to strongly correlated systems.

Highlights

In recent years, topological Kondo insulators [1] have emerged as a new class of materials where both the physics of strong electron correlations and/or topology could play a significant role
More recent studies further found significant sample variation in the low-temperature properties of these systems, depending on the synthesis methods and seed materials used [19,23,32,33]. Careful characterization of such samples indicates that even in the nominally purest samples, a minimal yet detectable amount (
In all our subsequent discussions based on the electronic density of states, we choose the d electrons, as they are the ones involved in the transport

Summary

Introduction

Topological Kondo insulators [1] have emerged as a new class of materials where both the physics of strong electron correlations and/or topology could play a significant role. Kondo insulators are strongly correlated systems in which a clean insulating gap emerges only at very low temperature due to many-body effects involving localized f electrons.

Results

Conclusion