77 research outputs found

    Non-Fermi liquid behavior in a fluctuating valence system, the filled skutterudite compound CeRu_{4}As_{12}

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    Electrical resistivity ρ\rho, specific heat C, and magnetic susceptibility χ\chi measurements made on the filled skutterudite CeRu_4As_{12} reveal non-Fermi liquid (NFL) T - dependences at low T, i.e., ρ\rho(T) \sim T^{1.4} and weak power law or logarithmic divergences in C(T)/T and χ\chi(T). Measurements also show that the T - dependence of the thermoelectric power S(T) deviates from that seen in other Ce systems. The NFL behavior appears to be associated with fluctuations of the Ce valence between 3^+ and 4^+ rather than a typical Kondo lattice scenario that would be appropriate for an integral Ce valence of 3^+.Comment: 18 pages, 5 figure

    Inelastic neutron scattering studies of Crystal Field Levels in PrOs4_4As12_{12}

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    We use neutron scattering to study the Pr3+^{3+} crystalline electric field (CEF) excitations in the filled skutterudite PrOs4_4As12_{12}. By comparing the observed levels and their strengths under neutron excitation with the theoretical spectrum and neutron excitation intensities, we identify the Pr3+^{3+} CEF levels, and show that the ground state is a magnetic Γ4(2)\Gamma_4^{(2)} triplet, and the excited states Γ1\Gamma_1, Γ4(1)\Gamma_4^{(1)} and Γ23\Gamma_{23} are at 0.4, 13 and 23 meV, respectively. A comparison of the observed CEF levels in PrOs4_4As12_{12} with the heavy fermion superconductor PrOs4_4Sb12_{12} reveals the microscopic origin of the differences in the ground states of these two filled skutterudites.Comment: 7 pages, 7 figure

    Existence of two-channel Kondo regime for tunneling impurities with resonant scattering

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    Dynamical tunneling systems have been proposed earlier to display a two-channel Kondo effect, the orbital index of the particle playing the role of a pseudospin in the equivalent Kondo problem, and the spin being a silent channel index. However, as shown recently by Aleiner et al. [Phys. Rev. Lett. 86, 2629 (2001)], the predicted two-channel Kondo behavior can never be observed in the weak coupling regime, where the tunneling induced splitting of the levels of the tunneling system always dominates the physics. Here we show that the above scenario changes completely if the conduction electrons are scattered by resonant scattering off the tunneling impurity; Then - as a non-perturbative analysis reveals - the two-channel Kondo regime can easily be reached.Comment: 10 PRB page

    A de Haas-van Alphen study of the filled skutterudite compounds PrOs4_4As12_{12} and LaOs4_4As12_{12}

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    Comprehensive magnetic-field-orientation dependent studies of the susceptibility and de Haas-van Alphen effect have been carried out on single crystals of the filled skutterudites PrOs4_4As12_{12} and LaOs4_4As12_{12} using magnetic fields of up to 40~T. Several peaks are observed in the low-field susceptibility of PrOs4_4As12_{12}, corresponding to cascades of metamagnetic transitions separating the low-field antiferromagnetic and high-field paramagnetic metal (PMM) phases. The de Haas-van Alphen experiments show that the Fermi-surface topologies of PrOs4_4As12_{12} in its PMM phase and LaOs4_4As12_{12} are very similar. In addition, they are in reasonable agreement with the predictions of bandstructure calculations for LaOs4_4As12_{12} on the PrOs4_4As12_{12} lattice. Both observations suggest that the Pr 4ff electrons contribute little to the number of itinerant quasiparticles in the PMM phase. However, whilst the properties of LaOs4_4As12_{12} suggest a conventional nonmagnetic Fermi liquid, the effects of direct exchange and electron correlations are detected in the PMM phase of PrOs4_4As12_{12}. For example, the quasiparticle effective masses in PrOs4_4As12_{12} are found to decrease with increasing field, probably reflecting the gradual suppression of magnetic fluctuations associated with proximity to the low-temperature, low-field antiferromagnetic state
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