Non-Kondo-like Electronic Structure in the Correlated Rare-Earth Hexaboride YbB$_6$

TL;DR

This study reveals that YbB$_6$ is a topological insulator with surface states not driven by Kondo physics, challenging previous predictions and suggesting new mechanisms for correlated topological phases.

Contribution

The paper demonstrates that YbB$_6$ hosts a topological insulator state independent of Kondo effects, supported by experimental ARPES data and first-principles calculations.

Findings

YbB$_6$ exhibits Dirac cone surface states at the Fermi level.

The f-orbital is about 1 eV below the Fermi level, not involved in the topological state.

The topological phase arises from band inversion between Yb d and B p bands.

Abstract

We present angle-resolved photoemission studies on the rare-earth hexaboride YbB$_6$, which has recently been predicted to be a topological Kondo insulator. Our data do not agree with the prediction and instead show that YbB$_6$ exhibits a novel topological insulator state in the absence of a Kondo mechanism. We find that the Fermi level electronic structure of YbB$_6$ has three 2D Dirac cone like surface states enclosing the Kramers' points, while the f-orbital which would be relevant for the Kondo mechanism is $\sim1$ eV below the Fermi level. Our first-principles calculation shows that the topological state which we observe in YbB$_6$ is due to an inversion between Yb $d$ and B $p$ bands. These experimental and theoretical results provide a new approach for realizing novel correlated topological insulator states in rare-earth materials.