Surface and Bulk Electronic Structure of the Strongly Correlated System SmB$_{6}$ and Implications for a Topological Kondo Insulator

TL;DR

This study uses angle-resolved photoemission spectroscopy to investigate the electronic structure of SmB$_{6}$, revealing bulk hybridized bands, a Kondo gap, and surface states that support its classification as a topological Kondo insulator.

Contribution

The paper provides experimental evidence of surface states and bulk hybridization in SmB$_{6}$, supporting its status as a topological Kondo insulator, which was not conclusively demonstrated before.

Findings

Identification of a bulk hybridized 5d band at the X point

Observation of a Kondo bandgap of approximately 20 meV

Detection of surface states consistent with topological insulator behavior

Abstract

Recent theoretical calculations and experimental results suggest that the strongly correlated material SmB$_{6}$ may be a realization of a topological Kondo insulator. We have performed an angle-resolved photoemission spectroscopy study on SmB$_{6}$ in order to elucidate elements of the electronic structure relevant to the possible occurrence of a topological Kondo insulator state. The obtained electronic structure in the whole three-dimensional momentum space reveals one electron-like 5d bulk band centred at the X point of the bulk Brillouin zone that is hybridized with strongly correlated f electrons, as well as the opening of a Kondo bandgap ($\Delta_B$ $\sim$ 20 meV) at low temperature. In addition, we observe electron-like bands forming three Fermi surfaces at the center $\bar{\Gamma}$ point and boundary $\bar{X}$ point of the surface Brillouin zone. These bands are not expected from calculations of the bulk electronic structure, and their observed dispersion characteristics are consistent with surface states. Our results suggest that the unusual low-temperature transport behavior of SmB$_{6}$ is likely to be related to the pronounced surface states sitting inside the band hybridisation gap and/or the presence of a topological Kondo insulating state.