Intermediate-valence Yb-based quasicrystals and approximants

Watanuki, Tetsu; Kawana, Daichi*; Machida, Akihiko; Kashimoto, Shiro*; Ishimasa, Tsutomu*; Tsai, A. P.*

Intermediate-valence (IV) quasicrystals, namely a new group of quasiperiodic system possessing a charge degree of freedom, were realized. First we have prepared IV quasicrystals by applying pressure to Yb-based quasicrystals. X-ray absorption spectroscopy study on an icosahedral Cd-Mg-Yb quasicrystal demonstrated that the Yb valence increased continuously upon compression from the divalent state (4f) at ambient pressure and reached a value of 2.71+ at 57.6 GPa, which is close to the trivalent state (4f). Next we searched for IV quasicrystals at ambient pressure. We have found that an icosahedral Au-Al-Yb quasicrystal forms an IV system with the mean Yb valence of 2.61+ at ambient pressure. Additionally specific heat and magnetization measurements have revealed non-Fermi-liquid behavior of this quasicrystal at low temperatures without either doping, pressure, or field tuning.