We study the electronic structure of Tsai-type cluster-based quasicrystalline approximants, Au64Ge22Yb14 (AGY-I), Au63.5Ge20.5Yb16 (AGY-II), and Zn85.4Yb14.6 (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 4f 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 4f 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.
@article{arxiv.1712.04113,
title = {Direct observation of heterogeneous valence state in Yb-based quasicrystalline approximants},
author = {M. Matsunami and M. Oura and K. Tamasaku and T. Ishikawa and S. Ideta and K. Tanaka and T. Takeuchi and T. Yamada and A. P. Tsai and K. Imura and K. Deguchi and N. K. Sato and T. Ishimasa},
journal= {arXiv preprint arXiv:1712.04113},
year = {2017}
}