Quantum Criticality of the Heavy-Fermion Compound YbAuCu₄

Abstract

We have investigated evolution of transport and low-energy spin fluctuation properties of the heavy fermion compound YbAuCu₄ with the application of magnetic field, and found that the material can be driven from the originally antiferromagnetically (AFM) ordered ground state (Néel temperature T_N∼0.8 K) to a nonmagnetic Fermi liquid one through the field-tuned quantum critical point (QCP) at H_cr\\simeq13 kOe. The electrical resistivity measurement down to 55 mK in the vicinity of H_cr (T_N→0) provides evidence for the increase in the inelastic scattering of heavy electrons, and the ⁶³Cu spin-lattice relaxation rate 1⁄T₁T measurement down to 1.35 K near H_cr exhibits the occurrence of the AFM order instability. Temperature and field participating in the non-Fermi liquid (NFL) phenomena in the vicinity of H_cr are about one order higher in energy than those in YbRh₂Si₂ that has been intensively investigated as only one NFL material among the stoichiometric Yb-based compounds. It is mentioned that in both compound, the quasiparticle mass does not diverge but remains finite in the field-tuned QCP. An additional new information provided in this study is that the Kondo temperature T_K derived from the resisitivity maximum and/or the 1⁄T₁T maximum monotonically increases with increasing field, contrary to the increase in the localization character of f electrons.