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

TL;DR

This paper demonstrates that the Kondo insulating gap is highly fragile against disorder, which explains the metallic behaviors in topological Kondo insulators like SmB$_6$, challenging their presumed topological protection.

Contribution

It reveals that moderate disorder can fill the Kondo gap with states, undermining the insulating state and questioning the topological nature of these materials.

Findings

Disorder fills the Kondo gap with states, destroying insulating behavior.

The fragile Kondo gap explains metallic behaviors in SmB$_6$ and similar materials.

Topological protection may not hold in disordered Kondo insulators.

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.