1,163 research outputs found

    Realization of Strong Coupling Fixed Point in Multilevel Kondo Models

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    Impurity four- and six-level Kondo model, in which an ion is tunneling among four- and six-stable points and interacting with surrounding conduction electrons, are investigated by using the perturbative and numerical renormalization group methods. It is shown that purely orbital Kondo effects occur at low temperatures in these systems which are direct generalizations of the Kondo effect in the so-called two-level system. This result offers a good explanation for the enhanced and magnetically robust Sommerfeld coefficient observed in SmOs_4Sb_12 and some other filled-skutterudites.Comment: 3 pages, 3 figures, for proceedings of ASR-WYP-2005. To be published in Journal of Physical Society Japan supplemen

    Universality in heavy-fermion systems with general degeneracy

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    We discuss the relation between the T^{2}-coefficient of electrical resistivity AA and the T-linear specific-heat coefficient γ\gamma for heavy-fermion systems with general NN, where NN is the degeneracy of quasi-particles. A set of experimental data reveals that the Kadowaki-Woods relation; A/γ2=1105μΩ(Kmol/mJ)2A/\gamma^{2} = 1*10^{-5} {\mu\Omega}(K mol/mJ)^{2}, collapses remarkably for large-N systems, although this relation has been regarded to be commonly applicable to the Fermi-liquids. Instead, based on the Fermi-liquid theory we propose a new relation; A~/γ~2=1×105\tilde{A}/\tilde{\gamma}^2=1\times10^{-5} with A~=A/(1/2)N(N1)\tilde{A} = A/(1/2)N(N-1) and γ~=γ/(1/2)N(N1)\tilde{\gamma} = \gamma/(1/2)N(N-1). This new relation exhibits an excellent agreement with the data for whole the range of degenerate heavy-fermions.Comment: 2 figures, to appear in Phys. Rev. Let

    Bistability of the Nuclear Polarisation created through optical pumping in InGaAs Quantum Dots

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    We show that optical pumping of electron spins in individual InGaAs quantum dots leads to strong nuclear polarisation that we measure via the Overhauser shift (OHS) in magneto-photoluminescence experiments between 0 and 4T. We find a strongly non-monotonous dependence of the OHS on the applied magnetic field, with a maximum nuclear polarisation of 40% for intermediate magnetic fields. We observe that the OHS is larger for nuclear fields anti-parallel to the external field than in the parallel configuration. A bistability in the dependence of the OHS on the spin polarization of the optically injected electrons is found. All our findings are qualitatively understood with a model based on a simple perturbative approach.Comment: Phys Rev B (in press
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