22,317 research outputs found
Kondo resonance narrowing in d- and f-electron systems
By developing a simple scaling theory for the effect of Hund's interactions
on the Kondo effect, we show how an exponential narrowing of the Kondo
resonance develops in magnetic ions with large Hund's interaction. Our theory
predicts an exponential reduction of the Kondo temperature with spin S of the
Hund's coupled moment, a little-known effect first observed in d-electron
alloys in the 1960's, and more recently encountered in numerical calculations
on multi-band Hubbard models with Hund's interactions. We discuss the
consequences of Kondo resonance narrowing for the Mott transition in d-band
materials, particularly iron pnictides, and the narrow ESR linewidth recently
observed in ferromagnetically correlated f-electron materials.Comment: 4 pages, 3 figure
Layered Kondo lattice model for quantum critical beta-YbAlB4
We analyze the magnetic and electronic properties of the quantum critical
heavy fermion superconductor beta-YbAlB4, calculating the Fermi surface and the
angular dependence of the extremal orbits relevant to the de Haas--van Alphen
measurements. Using a combination of the realistic materials modeling and
single-ion crystal field analysis, we are led to propose a layered Kondo
lattice model for this system, in which two dimensional boron layers are Kondo
coupled via interlayer Yb moments in a state. This model fits
the measured single ion magnetic susceptibility and predicts a substantial
change in the electronic anisotropy as the system is pressure-tuned through the
quantum critical point.Comment: Fig.3 and 4 have been updated, typos corrected in v2. Published at
http://link.aps.org/doi/10.1103/PhysRevLett.102.07720
Itinerant Ferromagnetism in an Atom Trap
We propose an experiment to explore the magnetic phase transitions in
interacting fermionic Hubbard systems, and describe how to obtain the
ferromagnetic phase diagram of itinerant electron systems from these
observations. In addition signatures of ferromagnetic correlations in the
observed ground states are found: for large trap radii (trap radius ,
in units of coherence length ), ground states are topological in nature --
a "skyrmion" in 2D, and a "hedgehog" in 3D.Comment: Final Published version. References adde
On some new approaches to practical Slepian-Wolf compression inspired by channel coding
This paper considers the problem, first introduced by Ahlswede and Körner in 1975, of lossless source coding with coded side information. Specifically, let X and Y be two random variables such that X is desired losslessly at the decoder while Y serves as side information. The random variables are encoded independently, and both descriptions are used by the decoder to reconstruct X. Ahlswede and Körner describe the achievable rate region in terms of an auxiliary random variable. This paper gives a partial solution for the optimal auxiliary random variable, thereby describing part of the rate region explicitly in terms of the distribution of X and Y
Kondo effect and channel mixing in oscillating molecules
We investigate the electronic transport through a molecule in the Kondo
regime. The tunneling between the electrode and the molecule is asymmetrically
modulated by the oscillations of the molecule, i.e., if the molecule gets
closer to one of the electrodes the tunneling to that electrode will increase
while for the other electrode it will decrease. The system is described by a
two-channel Anderson model with phonon-assisted hybridization, which is solved
with the Wilson numerical renormalization group method. The results for several
functional forms of tunneling modulation are presented. For a linearized
modulation the Kondo screening of the molecular spin is caused by the even or
odd conduction channel. At the critical value of the electron-phonon coupling
an unstable two-channel Kondo fixed point is found. For a realistic modulation
the spin at the molecular orbital is Kondo screened by the even conduction
channel even in the regime of strong coupling. A universal consequence of the
electron-phonon coupling is the softening of the phonon mode and the related
instability to perturbations that break the left-right symmetry. When the
frequency of oscillations decreases below the magnitude of such perturbation,
the molecule is abruptly attracted to one of the electrodes. In this regime,
the Kondo temperature is enhanced and, simultaneously, the conductance through
the molecule is suppressed.Comment: published versio
Information of Structures in Galaxy Distribution
We introduce an information-theoretic measure, the Renyi information, to
describe the galaxy distribution in space. We discuss properties of the
information measure, and demonstrate its relationship with the probability
distribution function and multifractal descriptions. Using the First Look
Survey galaxy samples observed by the Infrared Array Camera onboard Spitzer
Space Telescope, we present measurements of the Renyi information, as well as
the counts-in-cells distribution and multifractal properties of galaxies in
mid-infrared wavelengths. Guided by multiplicative cascade simulation based on
a binomial model, we verify our measurements, and discuss the spatial selection
effects on measuring information of the spatial structures. We derive structure
scan functions at scales where selection effects are small for the Spitzer
samples. We discuss the results, and the potential of applying the Renyi
information to measuring other spatial structures.Comment: 25 pages, 8 figures, submitted to ApJ; To appear in The Astrophysical
Journal 2006, 644, 678 (June 20th
Fractionalized Fermi liquids
In spatial dimensions d >= 2, Kondo lattice models of conduction and local
moment electrons can exhibit a fractionalized, non-magnetic state (FL*) with a
Fermi surface of sharp electron-like quasiparticles, enclosing a volume
quantized by (\rho_a-1)(mod 2), with \rho_a the mean number of all electrons
per unit cell of the ground state. Such states have fractionalized excitations
linked to the deconfined phase of a gauge theory. Confinement leads to a
conventional Fermi liquid state, with a Fermi volume quantized by \rho_a (mod
2), and an intermediate superconducting state for the Z_2 gauge case. The FL*
state permits a second order metamagnetic transition in an applied magnetic
field.Comment: 4 pages, 1 figure; (v2) changed title and terminology, but content
largely unchanged; (v3) updated version to appear in PR
Globular Clusters and Dwarf Spheroidal Galaxies
Traditionally globular clusters and dwarf spheroidal galaxies have been
distinguished by using one or more of the following criteria: (1) mass, (2)
luminosity, (3) size, (4) mass-to-light ratio and (5) spread in metallicity.
However, a few recently discovered objects show some overlap between the
domains in parameter space that are occupied by galaxies and clusters. In the
present note it is shown that ellipticity can, in some cases, be used to help
distinguish between globular clusters and dwarf spheroidal galaxies.Comment: MNRAS (Letters), in pres
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