Observation of in-gap surface states in the Kondo insulator SmB6 by photoemission

TL;DR

This study uses ARPES to directly observe in-gap surface states in SmB6, supporting its classification as a topological Kondo insulator with surface states that vanish at higher temperatures.

Contribution

First direct ARPES evidence of dispersive in-gap surface states in SmB6, indicating their topological nature and clarifying the origin of in-gap states in this Kondo insulator.

Findings

Dispersive in-gap states cross the Fermi level

States show negligible kz dependence, indicating surface origin

In-gap states vanish around 150 K, correlating with gap closing

Abstract

Kondo insulators (KIs) are strongly correlated materials in which the interactions between 4f and conduction electrons lead to a hybridization gap opening at low temperature 1-2. SmB6 is a typical KI, but its resistivity does not diverge at low temperatures, which was attributed to some in-gap states 3-10. However after several decades of research, the nature and origin of the in-gap states remain unclear. Recent band calculation and transport measurements suggest that the in-gap states could actually be ascribed to topological surface states. SmB6 thus might be the first realization of topological Kondo insulator (TKI) 13, the strongly correlated version of topological insulator (TI) 11,12. Here by performing angle-resolved photoemission spectroscopy (ARPES), we directly observed several dispersive states within the hybridization gap of SmB6, which cross the Fermi level and show negligible kz dependence, indicative of their surface origin. Furthermore, the circular dichroism (CD) ARPES results of the in-gap states suggest the chirality of orbital momentum, and temperature dependent measurements have shown that the in-gap states vanish simultaneously with the hybridization gap around 150 K. These strongly suggest their possible topological origin.