Surface Kondo effect and non-trivial metallic state of the Kondo insulator YbB12.

Kenta Hagiwara,Taichi Okuda,Masaharu Matsunami,Kazuki Sumida,Ryu Yukawa,Koji Horiba,Shin-Ichi Kimura,Julien E Rault,Masaki Kobayashi,Kiyohisa Tanaka,Hiroshi Kumigashira,Patrick Le Fèvre,Hidetoshi Miyazaki,Fumitoshi Iga,Amina Taleb-Ibrahimi,Yoshiyuki Ohtsubo,François Bertran,Shin-Ichiro Ideta

doi:10.1038/ncomms12690

Abstract

A synergistic effect between strong electron correlation and spin–orbit interaction has been theoretically predicted to realize new topological states 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 shows temperature-dependent reconstruction corresponding to the Kondo effect observed for bulk states. Despite the low-temperature insulating bulk, the reconstructed SS with c–f hybridization is metallic, forming a closed Fermi contour surrounding on the surface Brillouin zone and agreeing with the theoretically expected behaviour 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.

Highlights

A synergistic effect between strong electron correlation and spin–orbit interaction has been theoretically predicted to realize new topological states of quantum matter on Kondo insulators (KIs), so-called topological Kondo insulators (TKIs)
Such materials are categorized as topological Kondo insulators (TKIs) in which the topological surface states (SS) originate from c–f gap formation owing to the Kondo effect
TKIs are new physical states of quantum matter driven by the synergistic effect between strong electron correlation and spin–orbit interaction (SOI)

Summary

Introduction

A synergistic effect between strong electron correlation and spin–orbit interaction has been theoretically predicted to realize new topological states of quantum matter on Kondo insulators (KIs), so-called topological Kondo insulators (TKIs). Non-trivial surface electronic structures such as surface metallic states of topological insulators and giant Rashba-type spin splitting of polar semiconductors have been observed. These electronic structures originate from the large spin–orbit interaction (SOI) of heavy elements. In the case that the c–f gap is formed by the conduction and valence bands with inverted parities, two-dimensional (2D) metallic electronic states should always appear on the KI surface as in the case of topological insulators9,10 Such materials are categorized as topological Kondo insulators (TKIs) in which the topological surface states (SS) originate from c–f gap formation owing to the Kondo effect. A clear energy gap appears in the bulk of YbB12 with a gap size of about

Methods

Results

Conclusion