Surface Kondo Effect and Non-Trivial Metallic State of the Kondo Insulator YbB12

TL;DR

This study reveals a metallic surface state on YbB12(001), a candidate topological Kondo insulator, showing temperature-dependent reconstruction linked to the Kondo effect, supporting the existence of topological surface states in Kondo insulators.

Contribution

It provides experimental evidence of a temperature-dependent metallic surface state on YbB12(001), advancing understanding of topological Kondo insulators and surface state behavior.

Findings

Metallic surface state observed on YbB12(001)

Surface state shows temperature-dependent reconstruction

Surface state forms a closed Fermi contour around ar{ ext{G}}amma

Abstract

A synergistic effect between strong electron correlation and spin-orbit interaction (SOI) has been theoretically predicted to result in a new topological state of quantum matter on Kondo insulators (KIs), so-called topological Kondo insulators (TKIs). One TKI candidate has been experimentally observed on the KI SmB6(001), and the origin of the surface states (SS) and the topological order of SmB6 has been actively discussed. Here, we show a metallic SS on the clean surface of another TKI candidate YbB12(001), using angle-resolved photoelectron spectroscopy. The SS showed temperature-dependent reconstruction corresponding with the Kondo effect observed for bulk states. Despite the low-temperature insulating bulk, the reconstructed SS with c-f hybridization was metallic, forming a closed Fermi contour surrounding $\bar{\Gamma}$ on the surface Brillouin zone and agreeing with the theoretically expected behavior for SS on TKIs. These results demonstrate the temperature-dependent holistic reconstruction of two-dimensional states localized on KIs surface driven by the Kondo effect.