Intermediate Valence State in $\mathrm{YbB_4}$ Revealed by Resonant X-ray Emission Spectroscopy

TL;DR

This study uses resonant X-ray emission spectroscopy to investigate the temperature-dependent valence state of Yb in $ ext{YbB}_4$, revealing intermediate valence behavior and strong Kondo interactions that influence its magnetic properties.

Contribution

The paper provides the first detailed temperature-dependent valence analysis of $ ext{YbB}_4$ using resonant X-ray emission spectroscopy, highlighting its intermediate valence and Kondo behavior.

Findings

Yb valence increases from 2.61 to 2.67 between 12 K and 300 K.

$ ext{YbB}_4$ exhibits intermediate valence and strong Kondo interactions.

Zero-point valence is weakly dependent on Kondo temperature, not on valence change temperature.

Abstract

We report the temperature dependence of the Yb valence in the geometrically frustrated compound $\mathrm{YbB_4}$ from 12 to 300 K using resonant X-ray emission spectroscopy at the Yb $L_{\alpha_1}$ transition. We find that the Yb valence, $v$, is hybridized between the $v=2$ and $v=3$ valence states, increasing from $v=2.61\pm0.01$ at 12 K to $v=2.67\pm0.01$ at 300 K, confirming that $\mathrm{YbB_4}$ is a Kondo system in the intermediate valence regime. This result indicates that the Kondo interaction in $\mathrm{YbB_4}$ is substantial, and is likely to be the reason why $\mathrm{YbB_4}$ does not order magnetically at low temperature, rather than this being an effect of geometric frustration. Furthermore, the zero-point valence of the system is extracted from our data and compared with other Kondo lattice systems. The zero-point valence seems to be weakly dependent on the Kondo temperature scale, but not on the valence change temperature scale $T_v$.