Local moment behaviors of the valence fluctuating systems β-YbAlB 4 and α-YbAlB4

Abstract

β-YbAlB4 is the first example of an Yb-based heavy Fermion superconductor with Tc = 80 mK and exhibits pronounced non-Fermi-liquid behavior above Tc. On the other hand, recent hard x-ray photoemission spectroscopy measurements have revealed strong intermediate valence of both β-YbAlB4 and its locally isostructural polymorph α-YbAlB4 . Here we present the results of the specific heat and magnetization measurements of β-YbAlB4 and α-YbAlB4 . The results indicate a Fermi liquid ground state for α-YbAlB4 in contrast to the quantum criticality found in β-YbAlB4 . Interestingly, both systems exhibit Kondo lattice behavior with large Wilson ratio below T* ∼ 8K, through the renormalization of a high valence fluctuation scale ∼ 200 K. © Published under licence by IOP Publishing Ltd.