Topological surface state in the Kondo Insulator Samarium Hexaboride

TL;DR

This paper provides experimental evidence that SmB6 is a 3D topological insulator with a robust metallic surface state that is destroyed only when time reversal symmetry is broken, and explores the effects of doping on its topological properties.

Contribution

It demonstrates that SmB6 is a perfect 3D topological insulator with a nearly zero residual bulk conductivity and investigates how doping affects its surface state and topological nature.

Findings

Surface state is destroyed when time reversal symmetry is broken.

Doping induces a quantum percolation limit transforming the insulator.

SmB6 exhibits virtually zero residual bulk conductivity.

Abstract

Strongly correlated electron systems show many exotic properties such as unconventional superconductity, quantum criticality, and Kondo insulating behavior. In addition, the Kondo insulator SmB6 has been predicted theoretically to be a 3D topological insulator with a metallic surface state. We report here transport measurements on doped SmB6, which show that ~3% magnetic and non-magnetic dopants in SmB6 exhibit clearly contrasting behavior, evidence that the metallic surface state is only destroyed when time reversal symmetry is broken. We find as well a quantum percolation limit of impurity concentration which transform the topological insulator into a conventional band insulator by forming impurity band. Our careful thickness dependence results show that SmB6 is the first demonstatrated perfect 3D topological insulator with virtually zero residual bulk conductivity.