Valence Change Driven by Constituent Element Substitution in the   Mixed-Valence Quasicrystal and Approximant Au-Al-Yb
  Quantum criticality has been considered to be specific to crystalline materials such as heavy fermions. Very recently, however, the Tsai-type quasicrystal Au51Al34Yb15 has been reported to show unusual quantum critical behavior. To obtain a deeper understanding of this new material, we have searched for other Tsai-type cluster materials. Here, we report that the metal alloys Au44Ga41Yb15 and Ag47Ga38Yb15 are members of the 1/1 approximant to the Tsai-type quasicrystal and that both possess no localized magnetic moment. We suggest that the Au-Al-Yb system is located near the border of the divalent and trivalent states of the Yb ion; we also discuss a possible origin of the disappearance of magnetism, associated with the valence change, by the substitution of the constituent elements. 
Shuya Matsukawa, Katsumasa Tanaka, Mika Nakayama, Kazuhiko Deguchi,   Keiichiro Imura, Hiroyuki Takakura, Shiro Kashimoto, T...
cond-mat.str-el cond-mat.supr-con