Magnetic-field-induced reentrance of Fermi-liquid behavior and spin-lattice relaxation rates in YbCu5−xAux

A strong departure from Landau-Fermi liquid (LFL) behavior have been recently revealed in observed anomalies in both the magnetic susceptibility χ and the muon and 63Cu nuclear spin-lattice relaxation rates 1/T1 of YbCu5−xAux (x=0.6). We show that the above anomalies along with magnetic-field-induced reentrance of LFL properties are indeed determined by the dependence of the quasiparticle effective mass M∗ on magnetic field B and temperature T and demonstrate that violations of the Korringa law also come from M∗(B,T) dependence. We obtain this dependence theoretically utilizing our approach based on fermion condensation quantum phase transition (FCQPT) notion. Our theoretical analysis of experimental data on the base of FCQPT approach permits not only to explain the above two experimental facts in a unified manner, but to unveil their universal properties, relating the peculiar features of both longitudinal magnetoresistance and specific heat in YbRh2Si2 to the behavior of spin-lattice relaxation rates.