1,163 research outputs found
Realization of Strong Coupling Fixed Point in Multilevel Kondo Models
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
We discuss the relation between the T^{2}-coefficient of electrical
resistivity and the T-linear specific-heat coefficient for
heavy-fermion systems with general , where is the degeneracy of
quasi-particles. A set of experimental data reveals that the Kadowaki-Woods
relation; , 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;
with and .
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
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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