8,547 research outputs found
Evidence of metallic clustering in annealed Ga1-xMnxAs from atypical scaling behavior of the anomalous Hall coefficient
We report on the anomalous Hall coefficient and longitudinal resistivity
scaling relationships on a series of annealed Ga1-xMnxAs epilayers (x~0.055).
As-grown samples exhibit scaling parameter n of ~ 1. Near the optimal annealing
temperature, we find n ~ 2 to be consistent with recent theories on the
intrinsic origins of anomalous Hall Effect in Ga1-xMnxAs. For annealing
temperatures far above the optimum, we note n > 3, similar behavior to certain
inhomogeneous systems. This observation of atypical behavior agrees well with
characteristic features attributable to spherical resonance from metallic
inclusions from optical spectroscopy measurements.Comment: 3 pages, 3 figure
Interplay between carrier and impurity concentrations in annealed GaMnAs intrinsic anomalous Hall Effect
Investigating the scaling behavior of annealed GaMnAs anomalous
Hall coefficients, we note a universal crossover regime where the scaling
behavior changes from quadratic to linear, attributed to the anomalous Hall
Effect intrinsic and extrinsic origins, respectively. Furthermore, measured
anomalous Hall conductivities when properly scaled by carrier concentration
remain constant, equal to theoretically predicated values, spanning nearly a
decade in conductivity as well as over 100 K in T. Both the qualitative
and quantitative agreement confirms the validity of new equations of motion
including the Berry phase contributions as well as tunablility of the intrinsic
anomalous Hall Effect.Comment: 4 pages, 5 figure
Orbital ordering and enhanced magnetic frustration of strained BiMnO3 thin films
Epitaxial thin films of multiferroic perovskite BiMnO3 were synthesized on
SrTiO3 substrates, and orbital ordering and magnetic properties of the thin
films were investigated. The ordering of the Mn^{3+} e_g orbitals at a wave
vector (1/4 1/4 1/4) was detected by Mn K-edge resonant x-ray scattering. This
peculiar orbital order inherently contains magnetic frustration. While bulk
BiMnO3 is known to exhibit simple ferromagnetism, the frustration enhanced by
in-plane compressive strains in the films brings about cluster-glass-like
properties.Comment: 8 pages, 4 figures, accepted to Europhysics Letter
Cluster Model of Decagonal Tilings
A relaxed version of Gummelt's covering rules for the aperiodic decagon is
considered, which produces certain random-tiling-type structures. These
structures are precisely characterized, along with their relationships to
various other random tiling ensembles. The relaxed covering rule has a natural
realization in terms of a vertex cluster in the Penrose pentagon tiling. Using
Monte Carlo simulations, it is shown that the structures obtained by maximizing
the density of this cluster are the same as those produced by the corresponding
covering rules. The entropy density of the covering ensemble is determined
using the entropic sampling algorithm. If the model is extended by an
additional coupling between neighboring clusters, perfectly ordered structures
are obtained, like those produced by Gummelt's perfect covering rules.Comment: 10 pages, 20 figures, RevTeX; minor changes; to be published in Phys.
Rev.
Delay-induced Synchronization Phenomena in an Array of Globally Coupled Logistic Maps
We study the synchronization of a linear array of globally coupled identical
logistic maps. We consider a time-delayed coupling that takes into account the
finite velocity of propagation of the interactions. We find globally
synchronized states in which the elements of the array evolve along a periodic
orbit of the uncoupled map, while the spatial correlation along the array is
such that an individual map sees all other maps in his present, current, state.
For values of the nonlinear parameter such that the uncoupled maps are chaotic,
time-delayed mutual coupling suppress the chaotic behavior by stabilizing a
periodic orbit which is unstable for the uncoupled maps. The stability analysis
of the synchronized state allows us to calculate the range of the coupling
strength in which global synchronization can be obtained.Comment: 8 pages, 7 figures, changed content, added reference
Carbon States in Carbon-Encapsulated Nickel Nanoparticles Studied by Means of X-Ray Absorption, Emission, and Photoelectron Spectroscopies
Electronic structure of nickel nanoparticles encapsulated in carbon was
characterized by photoelectron, X-ray absorption, and X-ray emission
spectroscopies. Experimental spectra are compared with the density of states
calculated in the frame of the density functional theory. The carbon shell of
Ni nanoparticles has been found to be multilayer graphene with significant
(about 6%) amount of Stone--Wales defects. Results of the experiments evidence
protection of the metallic nanoparticles from the environmental degradation by
providing a barrier against oxidation at least for two years. Exposure in air
for 2 years leads to oxidation only of the carbon shell of Ni@C nanoparticles
with coverage of functional groups.Comment: 16 pages, 6 figures, accepted in J. Phys. Chem.
Fauriea, a new genus of the lecanoroid caloplacoid lichens (Teloschistaceae, lichen-forming ascomycetes)
The robust monophyletic branch having the highest level of bootstrap support in the phylogenetical tree of the Teloschistaceae based on combined data set of ITS, LSU nrDNA and 12S SSU mtDNA sequences, which does not belong to any other earlier proposed genera of the subfamily Caloplacoideae, is described as the new genus Fauriea S. Y. Kondr., L. Lőkös et J.-S. Hur, gen. nova for lecanoroid South Korean Caloplaca chujaensis, and newly described Eastern Chinese Fauriea orientochinensis. Descriptions of the new genus Fauriea and the species Fauriea orientochinensis, a comparison with closely related taxa and a discussion of their position are provided. New name Tayloriellina is proposed for the genus of the subfamily Brownlielloideae Tayloriella S. Y. Kondr., Kärnefelt, A. Thell, Elix et Hur (nom. illeg., non Tayloriella Kylin, Rhodomebaceae, Rhodophyta). New combinations for type species of the genera Fauriea and Tayloriellina (i.e.: Fauriea chujaensis (basionym: Caloplaca chujaensis S. Y. Kondr., L. Lőkös et J.-S. Hur), and Tayloriellina erythrosticta (basionym: Lecanora erythrosticta Taylor)) are proposed. Fauriea chejuensis and Biatora pseudosambuci are for the first time recorded for China
On Classical Equivalence Between Noncritical and Einstein Gravity : The AdS/CFT Perspectives
We find that noncritical gravity, a special class of higher derivative
gravity, is classically equivalent to Einstein gravity at the full nonlinear
level. We obtain the viscosity-to-entropy ratio and the second order transport
coefficients of the dual fluid of noncritical gravity to all orders in the
coupling of higher derivative terms. We also compute the holographic
entanglement entropy in the dual CFT of noncritical gravity. All these results
confirm the nonlinear equivalence between noncritical gravity and Einstein
gravity at the classical level.Comment: 19 pages, no figure
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