Non-Fermi liquid behavior of U-impurity with f2-singlet ground state

It is shown by the Wilson numerical renormalization-group approach that a U-impurity with an f(2)-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 R1-xUxRU2Si2 (R=Th, Y and La, x less than or equal to 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 Th1-xUxRU2Si2. Less anomalous properties of R1-xUxSi2 (R=Y and La) can be understood in the same scenario provided that these compounds have different sets of parameters.