23,040 research outputs found
An Enhanced Perturbational Study on Spectral Properties of the Anderson Model
The infinite- single impurity Anderson model for rare earth alloys is
examined with a new set of self-consistent coupled integral equations, which
can be embedded in the large expansion scheme ( is the local spin
degeneracy). The finite temperature impurity density of states (DOS) and the
spin-fluctuation spectra are calculated exactly up to the order . The
presented conserving approximation goes well beyond the -approximation
({\em NCA}) and maintains local Fermi-liquid properties down to very low
temperatures. The position of the low lying Abrikosov-Suhl resonance (ASR) in
the impurity DOS is in accordance with Friedel's sum rule. For its shift
toward the chemical potential, compared to the {\em NCA}, can be traced back to
the influence of the vertex corrections. The width and height of the ASR is
governed by the universal low temperature energy scale . Temperature and
degeneracy -dependence of the static magnetic susceptibility is found in
excellent agreement with the Bethe-Ansatz results. Threshold exponents of the
local propagators are discussed. Resonant level regime () and intermediate
valence regime () of the model are thoroughly
investigated as a critical test of the quality of the approximation. Some
applications to the Anderson lattice model are pointed out.Comment: 19 pages, ReVTeX, no figures. 17 Postscript figures available on the
WWW at http://spy.fkp.physik.th-darmstadt.de/~frithjof
Composite Spin-Triplet Superconductivity in an Symmetric Lattice Model
The two-channel Anderson lattice model which has
symmetry is of relevance to understanding of the magnetic, quadrupolar and
superconducting phases in UThBe or Pr base skutterudite
compounds such as PrFeP or PrOsSb. Possible
unconventional superconducting phases of the model are explored. They are
characterized by a composite order parameter comprising of a local magnetic or
quadrupolar moment and a triplet conduction electron Cooper-pair. This binding
of local degrees of freedom removes the entropy of the non Fermi-liquid normal
state. We find superconducting transitions in the intermediate valence regime
which are suppressed in the stable moment regime. The gap function is non
analytic and odd in frequency: a pseudo-gap develops in the conduction electron
density of states which vanishes as close to . In the
strong intermediate valent regime, the gap function acquires an additional
\k-dependence.Comment: 20 pages, 12 figures, latex EPJ format. Accepted for publication as
Eur.Phys.J.
Airfoil large eddy breakup devices for turbulent drag reduction
It was determined from the present LaRC experiments that tandem, airfoil-shaped large eddy breakup (LEBU) devices can reduce local skin friction as much as 30 percent with a recovery region extending more than 100 boundary layer thicknesses downstream. These airfoils experience near laminar skin friction device drag and produce net drag reductions of up to 7 percent. In contrast to the thin plates used in previous experiments, these airfoils are more than 1000 time stiffer and hence have the potential to withstand the real flight environment (dynamic pressure 36 times larger than in low-speed wing tunnels). In addition, the higher Reynolds numbers of the present tests indicate drag reduction performance is at least as good (or better) as at lower Reynolds numbers
Comment on "Scaling feature of magnetic field induced Kondo-peak splittings"
In a recent work Zhang and coworkers (PRB 82, 075111 (2010)) studied the
Zeeman splitting of the Kondo resonance for the single impurity Anderson model
in a finite magnetic field with the numerical renormalization group (NRG)
method. There, it was found that with increasing magnetic field the
position of the Kondo resonance in the total spectral function \textit{does
not} approach its position in the spin resolved spectral function.
Additionally, the position of the Kondo maximum exceeded the Zeeman energy for
, where is the low energy Kondo scale of the model
(, ). In this comment we argue that both these findings
are produced by an improper choice of NRG parameter values. However, we
reproduce the crossover in the splitting from Kondo-like behavior to a
non-universal splitting larger than the Zeeman energy, but this crossover
occurs at much larger fields of the order of the charge scale.Comment: Minor revisions; same version as publishe
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