Non-Fermi Liquid Behavior of U-impurity withf²-Singlet Ground State

Abstract

It is shown by the Wilson's numerical renormalization-group approach that Non-Fermi liquid (NFL) behaviors arise even for U-impurity with an f 2 -singlet ground state, and all the puzzling behaviors of R1−xUxRu2Si2 (R=Th, Y and La, x ≤ 0.07) can be explained on its basis. There exists an unstable NFL fixed point due to the balance between Kondo singlet and CrystallineElectric-Field singlet ground states. For wide region in parameter space the system shows the NFL behavior as a transient phenomenon in temperature range accessible by experiment. Results for temperature dependence of the resistivity, the magnetic susceptibility and the Sommerfeld coefficient with and without magnetic field reproduce the behaviors observed in Th1−xUxRu2Si2. Less anomalous properties of R1−xUxRu2Si2 (R=Y and La) can be understood along the same scenario provided that those compounds have different sets of parameters.

Single-site effects of Pr and U ions doped in (, Y and La)

“…We thus conclude that the ''bare'' CEF effects at the R-ion site in RRu 2 Si 2 are those which lead to the singlet ground state for the 4f 2 configuration. This may support the theoretical predictions [8] that the hybridization effects competing with the CEF singlet ground state may bring about the various low-T singularities observed in the uranium dilute systems. As mentioned above, however, the key to the application of the singlet-singlet model would be how to account for the strong uniaxial magnetic anisotropy observed in all the dilute alloys as well as the related periodic compounds such as UðRu; RhÞ 2 Si 2 .…”

“…0Þ [6,7], but disagree with the behavior of the specific heat in magnetic field, which shows the absence of the residual entropy [1]. On the other hand, the numerical renormalization group study for the f 2 -impurity Anderson model, based on the CEF singlet ground state, predicts the crossover between the NFL and local Fermi-liquid states [8]. The ground state does not involve the residual entropy, which is consistent with the experimental results.…”

Local Nodal Cooper Pairs in Multiorbital Systems

“…We start first by demonstrating that low-energy effective interactions in such * E-mail: hattori@tmu.ac.jp multiorbital models with the spin-orbit interaction (SOI) are completely different from the conventional Hubbardtype parametrization, and include e.g. antiferro Hund's coupling 9) and enhanced interorbital interactions.…”

Numerical renormalization group study of quasiparticle interactions for -impurity Anderson model

“…We also ignore J ¼ 7 2 states, assuming large spin-orbit interaction. It is noted that J z ojJ AE j and J AE o0 in order to reproduce the f 2 CEF configuration, which is anti-ferromagnetic Hund's rule coupling [6]. There are two excited states: G 5 (doublet) and G 3 (singlet).…”

“…1: There are two stable fixed points, Kondo-Yosida (KY) singlet fixed point and f 2 -CEF singlet one. Between them, there is an unstable fixed point corresponding to non-Fermi liquid (NFL) [6]. Around KY singlet fixed point, we can write down the effective Hamiltonian as …”