16,956 research outputs found
Comparison of methods for estimating continuous distributions of relaxation times
The nonparametric estimation of the distribution of relaxation times approach
is not as frequently used in the analysis of dispersed response of dielectric
or conductive materials as are other immittance data analysis methods based on
parametric curve fitting techniques. Nevertheless, such distributions can yield
important information about the physical processes present in measured
material. In this letter, we apply two quite different numerical inversion
methods to estimate the distribution of relaxation times for glassy \lila\
dielectric frequency-response data at 225 \kelvin. Both methods yield unique
distributions that agree very closely with the actual exact one accurately
calculated from the corrected bulk-dispersion Kohlrausch model established
independently by means of parametric data fit using the corrected modulus
formalism method. The obtained distributions are also greatly superior to those
estimated using approximate functions equations given in the literature.Comment: 4 pages and 4 figure
Coordinate shift in the semiclassical Boltzmann equation and the anomalous Hall effect
We propose a gauge invariant expression for the side jump associated with
scattering between particular Bloch states. Our expression for the side jump
follows from the Born series expansion for the scattering T-matrix in powers of
the strength of the scattering potential. Given our gauge invariant side jump
expression, it is possible to construct a semiclassical Boltzmann theory of the
anomalous Hall effect which expresses all previously identified contributions
in terms of gauge invariant quantities and does not refer explicitly to
off-diagonal terms in the density-matrix response.Comment: 6 pages, 1 fugure. submitted to PR
Charge and spin Hall conductivity in metallic graphene
Graphene has an unusual low-energy band structure with four chiral bands and
half-quantized and quantized Hall effects that have recently attracted
theoretical and experimental attention. We study the Fermi energy and disorder
dependence of its spin Hall conductivity. In the metallic regime we find that
vertex corrections enhance the intrinsic spin Hall conductivity and that skew
scattering can lead to its values that exceed the quantized ones expected when
the chemical potential is inside the spin-orbit induced energy gap. We predict
that large spin Hall conductivities will be observable in graphene even when
the spin-orbit gap does not survive disorder.Comment: 4 pages, 2 figure
Current noise of a quantum dot p-i-n junction in a photonic crystal
The shot-noise spectrum of a quantum dot p-i-n junction embedded inside a
three-dimensional photonic crystal is investigated. Radiative decay properties
of quantum dot excitons can be obtained from the observation of the current
noise. The characteristic of the photonic band gap is revealed in the current
noise with discontinuous behavior. Applications of such a device in
entanglement generation and emission of single photons are pointed out, and may
be achieved with current technologies.Comment: 4 pages, 3 figures, to appear in Phys. Rev. B (2005
A Note on the Pfaffian Integration Theorem
Two alternative, fairly compact proofs are presented of the Pfaffian
integration theorem that is surfaced in the recent studies of spectral
properties of Ginibre's Orthogonal Ensemble. The first proof is based on a
concept of the Fredholm Pfaffian; the second proof is purely linear-algebraic.Comment: 8 pages; published versio
Eigenvalue Separation in Some Random Matrix Models
The eigenvalue density for members of the Gaussian orthogonal and unitary
ensembles follows the Wigner semi-circle law. If the Gaussian entries are all
shifted by a constant amount c/Sqrt(2N), where N is the size of the matrix, in
the large N limit a single eigenvalue will separate from the support of the
Wigner semi-circle provided c > 1. In this study, using an asymptotic analysis
of the secular equation for the eigenvalue condition, we compare this effect to
analogous effects occurring in general variance Wishart matrices and matrices
from the shifted mean chiral ensemble. We undertake an analogous comparative
study of eigenvalue separation properties when the size of the matrices are
fixed and c goes to infinity, and higher rank analogues of this setting. This
is done using exact expressions for eigenvalue probability densities in terms
of generalized hypergeometric functions, and using the interpretation of the
latter as a Green function in the Dyson Brownian motion model. For the shifted
mean Gaussian unitary ensemble and its analogues an alternative approach is to
use exact expressions for the correlation functions in terms of classical
orthogonal polynomials and associated multiple generalizations. By using these
exact expressions to compute and plot the eigenvalue density, illustrations of
the various eigenvalue separation effects are obtained.Comment: 25 pages, 9 figures include
Basic Representations of A_{2l}^(2) and D_{l+1}^(2) and the Polynomial Solutions to the Reduced BKP Hierarchies
Basic representations of A_{2l}^(2) and D_{l+1}^(2) are studied. The weight
vectors are represented in terms of Schur's -functions. The method to get
the polynomial solutions to the reduced BKP hierarchies is shown to be
equivalent to a certain rule in Maya game.Comment: January 1994, 11 page
Gel'fand-Zetlin Basis and Clebsch-Gordan Coefficients for Covariant Representations of the Lie superalgebra gl(m|n)
A Gel'fand-Zetlin basis is introduced for the irreducible covariant tensor
representations of the Lie superalgebra gl(m|n). Explicit expressions for the
generators of the Lie superalgebra acting on this basis are determined.
Furthermore, Clebsch-Gordan coefficients corresponding to the tensor product of
any covariant tensor representation of gl(m|n) with the natural representation
V ([1,0,...,0]) of gl(m|n) with highest weight (1,0,. . . ,0) are computed.
Both results are steps for the explicit construction of the parastatistics Fock
space.Comment: 16 page
Electron-electron interactions in decoupled graphene layers
Multi-layer graphene on the carbon face of silicon carbide is an intriguing
electronic system which typically consists of a stack of ten or more layers.
Rotational stacking faults in this system dramatically reduce inter-layer
coherence. In this article we report on the influence of inter-layer
interactions, which remain strong even when coherence is negligible, on the
Fermi liquid properties of charged graphene layers. We find that inter-layer
interactions increase the magnitudes of correlation energies and decrease
quasiparticle velocities, even when remote-layer carrier densities are small,
and that they lessen the influence of exchange and correlation on the
distribution of carriers across layers.Comment: 8 pages, 4 figures, submitte
Noise spectroscopy and interlayer phase-coherence in bilayer quantum Hall systems
Bilayer quantum Hall systems develop strong interlayer phase-coherence when
the distance between layers is comparable to the typical distance between
electrons within a layer. The phase-coherent state has until now been
investigated primarily via transport measurements. We argue here that
interlayer current and charge-imbalance noise studies in these systems will be
able to address some of the key experimental questions. We show that the
characteristic frequency of current-noise is that of the zero wavevector
collective mode, which is sensitive to the degree of order in the system. Local
electric potential noise measured in a plane above the bilayer system on the
other hand is sensitive to finite-wavevector collective modes and hence to the
soft-magnetoroton picture of the order-disorder phase transition.Comment: 5 pages, 2 figure
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