Direct observation of heterogeneous valence state in Yb-based quasicrystalline approximants

TL;DR

This study uses photoemission spectroscopy to reveal heterogeneous valence states in Yb-based quasicrystalline approximants, showing distinct electronic configurations linked to different Yb sites within the structures.

Contribution

It provides direct experimental evidence of heterogeneous Yb valence states in quasicrystalline approximants, highlighting site-specific electronic differences.

Findings

Heterogeneous valence states observed in AGY-II and Zn-Yb.

Distinct Yb 4f electronic signals linked to different Yb sites.

Absence of fully occupied 4f state in AGY-I without Yb in the cluster center.

Abstract

We study the electronic structure of Tsai-type cluster-based quasicrystalline approximants, Au$_{64}$Ge$_{22}$Yb$_{14}$ (AGY-I), Au$_{63.5}$Ge$_{20.5}$Yb$_{16}$ (AGY-II), and Zn$_{85.4}$Yb$_{14.6}$ (Zn-Yb), by means of photoemission spectroscopy. In the valence band hard x-ray photoemission spectra of AGY-II and Zn-Yb, we separately observe a fully occupied Yb 4$f$ state and a valence fluctuation derived Kondo resonance peak, reflecting two inequivalent Yb sites, a single Yb atom in the cluster center and its surrounding Yb icosahedron, respectively. The fully occupied 4$f$ signal is absent in AGY-I containing no Yb atom in the cluster center. The results provide direct evidence for a heterogeneous valence state in AGY-II and Zn-Yb.