Hybridization, Inter-Ion Correlation, and Surface States in the Kondo Insulator SmB6

TL;DR

This study uses point-contact spectroscopy to investigate the electronic structure of SmB6, revealing Kondo hybridization, inter-ion correlations, and surface conduction states, supporting its classification as a topological Kondo insulator.

Contribution

It provides direct experimental evidence of the temperature-dependent evolution of electronic states and surface conduction in SmB6, highlighting the interplay of Kondo hybridization and topological surface states.

Findings

Kondo hybridization observed below 100 K

Inter-ion correlation effects emerge below 30 K

Surface conduction states support topological insulator behavior

Abstract

As an exemplary Kondo insulator, SmB6 has been studied for several decades; however, direct evidence for the development of the Kondo coherent state and the evolution of the electronic structure in the material has not been obtained due to the rather complicated electronic and thermal transport behavior. Recently, these open questions attracted increasing attention as the emergence of a time-reversal invariant topological surface state in the Kondo insulator has been suggested. Here, we use point-contact spectroscopy to reveal the temperature dependence of the electronic states in SmB6. We demonstrate that SmB6 is a model Kondo insulator: below 100 K, the conductance spectra reflect the Kondo hybridization of Sm ions, but below ~ 30 K, signatures of inter-ion correlation effects clearly emerge. Moreover, we find evidence that the low-temperature insulating state of this exemplary Kondo lattice compound harbors conduction states on the surface, in support of predictions of nontrivial topology in Kondo insulators.