New quantum criticality revealed under pressure

Unconventional quantum critical phenomena observed in Yb-based periodic crystals such as YbRh₂Si₂ and β-YbAlB₄ have been one of the central issues in strongly correlated electron systems. The common criticality has been discovered in the quasicrystal Yb₁₅Au₅₁Al₃₄, which surprisingly persists under pressure at least up to P = 1.5 GPa. The T/H scaling where the magnetic susceptibility can be expressed as a single scaling function of the ratio of the temperature T to the magnetic field H has been discovered in the quasicrystal, which is essentially the same as that observed in β-YbAlB₄. Recently, the T/H scaling as well as the common criticality has also been observed even in the approximant crystal Yb₁₄Au₅₁Al₃₅ under pressure. The theory of critical Yb-valence fluctuation gives a natural explanation for these striking phenomena in a unified way. (author)