Non-Fermi liquid phenomena and intermediate valence in Yb-based compounds located close to the quantum critical point

Abstract

In this paper, we focus on the mechanism of non-Fermi liquid phenomena in the vicinity of the magnetic field-tuned quantum critical point in Yb-based heavy fermion compounds YbAuCu 4, YbRh 2Si 2 and YbFe 4P 12. A comparative study of YbAuCu 4 and YbPdCu 4 with differently magnetically ordered ground states of antiferromagnetic (AFM) and ferromagnetic (FM) indicates that the competition between the field-destabilized AFM and field-stabilized FM correlations plays an important role on the field-tuned quantum critical behavior. The non-integer valence of these compounds leads to a consideration that the experimental susceptibility is dominated by the weakly broadened 4f hole level above the Fermi sea that extends to the cf hybridized band located at the Fermi level. Whilst, the monotonic increase of T 0 (an estimate of Kondo temperature) with field, derived from the transport and spin-fluctuation measurements, is ascribed to the variation of conduction bands from a weakly cf hybridized band toward the originally underlying conduction bands. The important role of the crossover transition upon cooling from the mixed valence localized f hole state to an itinerant electron state with the intermediate valence is also suggested.