Topological Crystalline Kondo Insulator in Mixed Valence Ytterbium Borides

TL;DR

This paper investigates the electronic structures of YbB$_6$ and YbB$_12$, revealing YbB$_6$ as a topological insulator and YbB$_12$ as a novel strongly correlated topological crystalline Kondo insulator with distinct surface states.

Contribution

It introduces YbB$_12$ as a new type of strongly correlated topological crystalline Kondo insulator with a non-zero mirror Chern number, expanding the understanding of topological phases in mixed valence ytterbium borides.

Findings

YbB$_6$ is a Z$_2$ topological insulator with a large bulk band gap.

YbB$_12$ is a strongly correlated topological crystalline Kondo insulator.

YbB$_6$ has three Dirac cones on the surface, YbB$_12$ has four.

Abstract

The electronic structures of two mixed valence insulators YbB$_6$ and YbB$_12$ are studied by using the local density approximation (LDA) supplemented with the Gutzwiller method and dynamic mean field theory (DMFT). YbB$_6$ is found to be a moderately correlated Z$_2$ topological insulator, similar to SmB$_6$ but having much larger bulk band gap. Notably, YbB$_12$ is revealed to be in a new novel quantum state, strongly correlated topological crystalline Kondo insulator, which is characterized by its non-zero mirror Chern number. The surface calculations find odd (three) and even (four) number of Dirac cones for YbB$_6$ and YbB$_12$, respectively.