Hybridization gap formation in the Kondo insulator YbB$_{12}$ observed using time-resolved photoemission spectroscopy

TL;DR

This study uses advanced photoemission spectroscopy techniques to reveal the formation of a hybridization gap in the Kondo insulator YbB$_{12}$, showing a pseudogap and long recombination times below a crossover temperature.

Contribution

It combines ultrahigh-resolution and time-resolved photoemission spectroscopy to directly observe the development of a hybridization gap in YbB$_{12}$, providing new insights into its electronic structure.

Findings

Identification of a 25-meV pseudogap related to the Kondo temperature.

Observation of a 15-meV gap and Kondo-peak feature below 110 K.

Detection of recombination times exceeding 100 ps indicating a hybridization gap.

Abstract

A detailed low-energy electronic structure of a Kondo insulator YbB$_{12}$ was revealed by a synergetic combination of ultrahigh-resolution laser photoemission spectroscopy (PES) and time-resolved PES. The former confirmed a 25-meV pseudogap corresponding to the Kondo temperature of this material, and more importantly, it revealed that a 15-meV gap and a Kondo-peak feature developed below a crossover temperature $T^\ast \sim 110$ K. In harmony with this, the latter discovered a very long recombination time exceeding 100 ps below $\sim$$T^\ast$. This is a clear manifestation of photoexcited carriers due to the bottleneck in the recovery dynamics, which is interpreted as a developing hybridization gap of a hard gap.