Magnetic Field Effect on Crossover Temperature from Non-Fermi Liquid to Fermi Liquid Behavior in f^2-Impurity Systems with Crystalline-Electric-Field Singlet State Competing with Kondo-Yosida Singlet State

摘要

We investigate the magnetic field dependence of the physical properties off^2-configuration systems with a crystalline-electric field (CEF) singletground state, which gives rise to a non- Fermi liquid (NFL) fixed point due tothe competition between the Kondo-Yosida singlet and CEF singlet states. On thebasis of the numerical renormalization group method, we find that the magneticfield breaks this NFL fixed point via two mechanisms: one causing thepolarization of f-electrons and the other giving the "channel" anisotropy.These two mechanisms induce a difference in the magnetic field dependence ofthe characteristic temperature T_F^{*}(H), the crossover temperature from NFLto Fermi-liquid behavior. While the polarization of f-electrons givesT_F^{*}(H) \propto H^x (x\sim2.0), the "channel" anisotropy gives theH-independent T_F^{*}(H). These two mechanisms cross over continuously atapproximately the crossover magnetic field H_c, where an anomalous H-dependenceof T_F^{*}(H) appears. Such T_F^{*}(H) well reproduces the NFL behaviorsobserved in Th_{1-x}U_xRu_2Si_2. We also find that the H-dependence of theresistivity and the magnetic susceptibility are in good agreement with theexperimental results of this material. These results suggest that the NFLbehaviors observed in Th_{1-x}U_xRu_2Si_2 can be understood if this material islocated in the CEF singlet side near the critical phase boundary between thetwo singlet states.