Non-Fermi Liquid Behavior of U-impurity with f²-Singlet Ground State

Abstract

It is shown by the Wilson numerical renormalization-group approach that a U-impurity with an f²-singlet ground state exhibits an unstable non-Fermi liquid (NFL) fixed point due to the balance between Kondo singlet and crystalline-electric-field singlet ground state. The puzzling behavior of R_1-xU_xRu₂Si₂ (R=Th, Y and La, x≤ 0.07) can be explained if we assume that the singlet ground state is realized and the Kondo temperatures in each orbital are of different orders of magnitude. For a wide region in parameter space, the system shows the NFL behavior as a transient phenomenon in a experimentally possible temperature range. Results for the temperature dependence of resistivity, magnetic susceptibility and the Sommerfeld coefficient with and without a magnetic field reproduce the behavior observed in Th_1-xU_xRu₂Si₂. Less anomalous properties of R_1-xU_xRu₂Si₂ (R=Y and La) can be understood in the same scenario provided that these compounds have different sets of parameters.