Kondo Lattice Behavior in the Valence Fluctuating Systems alpha - and beta -YbAlB sub( 4)

We have measured specific heat and magnetization of the Yb-based heavy Fermion systems alpha -YbAlB ... and ...-YbAlB ... . alpha -YbAlB ... is a locally isostructural polymorph of the first example of an Yb-based heavy Fermion superconductor beta -YbAlB ... , which exhibits pronounced non-Fermi-liquid behavior above the superconducting transition temperature T ... = 80 mK. The results reveal a Fermi liquid ground state for alpha -YbAlB ... in contrast to the quantum criticality found for beta -YbAlB ... . Interestingly, both systems exhibit Kondo lattice behavior with its characteristic temperature scale T * ~8 K, despite of their strongly intermediate valence with the temperature scale of ~ 200 K. We discuss the origin of this unusual behavior, making a comparison with the typical mixed valent compound YbAl ... . Large Wilson ratios indicate the existence of ferromagnetic correlation as a possible origin for the Kondo lattice behavior. (ProQuest: ... denotes formulae/symbols omitted.)