Intermediate-valence icosahedral Au-Al-Yb quasicrystal

Abstract

A quasiperiodic intermediate-valence (IV) system is realized in an icosahedral Au-Al-Yb quasicrystal. X-ray absorption spectroscopy near the Yb ${L}_{3}$ edge indicates that quasiperiodically arranged Yb ions assume a mean valence of 2.61, between a divalent state ($4{f}^{14}$, $J=0$) and a trivalent one ($4{f}^{13}$, $J=7/2$). Magnetization measurements demonstrate that the $4f$ holes in this quasicrystal have a localized character. The magnetic susceptibility shows a Curie-Weiss behavior above $\ensuremath{\sim}100$ K with an effective magnetic moment of 3.81${\ensuremath{\mu}}_{\mathrm{B}}$ per Yb. Moreover, a crystalline approximant to this quasicrystal is an IV compound. We propose a heterogeneous IV model for the quasicrystal, whereas the crystalline approximant is most likely a homogeneous IV system. At temperatures below $\ensuremath{\sim}10$ K, specific heat and magnetization measurements reveal non-Fermi-liquid behavior in both the quasicrystal and its crystalline approximant without either doping, pressure, or field tuning.