6,067 research outputs found
Universal finite size corrections and the central charge in non solvable Ising models
We investigate a non solvable two-dimensional ferromagnetic Ising model with
nearest neighbor plus weak finite range interactions of strength \lambda. We
rigorously establish one of the predictions of Conformal Field Theory (CFT),
namely the fact that at the critical temperature the finite size corrections to
the free energy are universal, in the sense that they are exactly independent
of the interaction. The corresponding central charge, defined in terms of the
coefficient of the first subleading term to the free energy, as proposed by
Affleck and Blote-Cardy-Nightingale, is constant and equal to 1/2 for all
0<\lambda<\lambda_0 and \lambda_0 a small but finite convergence radius. This
is one of the very few cases where the predictions of CFT can be rigorously
verified starting from a microscopic non solvable statistical model. The proof
uses a combination of rigorous renormalization group methods with a novel
partition function inequality, valid for ferromagnetic interactions.Comment: 43 pages, 1 figur
Electron Correlations in Bilayer Graphene
The nature of electron correlations in bilayer graphene has been
investigated. An analytic expression for the radial distribution function is
derived for an ideal electron gas and the corresponding static structure factor
is evaluated. We also estimate the interaction energy of this system. In
particular, the functional form of the pair-correlation function was found to
be almost insensitive to the electron density in the experimentally accessible
range. The inter-layer bias potential also has a negligible effect on the
pair-correlation function. Our results offer valuable insights into the general
behavior of the correlated systems and serve as an essential starting-point for
investigation of the fully-interacting system.Comment: 4 pages, 3 figure
Theory of water and charged liquid bridges
The phenomena of liquid bridge formation due to an applied electric field is
investigated. A new solution for the charged catenary is presented which allows
to determine the static and dynamical stability conditions where charged liquid
bridges are possible. The creeping height, the bridge radius and length as well
as the shape of the bridge is calculated showing an asymmetric profile in
agreement with observations. The flow profile is calculated from the Navier
Stokes equation leading to a mean velocity which combines charge transport with
neutral mass flow and which describes recent experiments on water bridges.Comment: 10 pages 12 figures, misprints corrected, assumptions more
transparen
Effect of nonhomogenous dielectric background on the plasmon modes in graphene double-layer structures at finite temperatures
We have calculated the plasmon modes in graphene double layer structures at
finite temperatures, taking into account the inhomogeneity of the dielectric
background of the system. The effective dielectric function is obtained from
the solution of the Poisson equation of three-layer dielectric medium with the
graphene sheets located at the interfaces, separating the different materials.
Due to the momentum dispersion of the effective dielectric function, the intra-
and inter-layer bare Coulomb interactions in the graphene double layer system
acquires an additional momentum dependence--an effect that is of the order of
the inter-layer interaction itself. We show that the energies of the in-phase
and out-of-phase plasmon modes are determined largely by different values of
the spatially dependent effective dielectric function. The effect of the
dielectric inhomogeneity increases with temperature and even at high
temperatures the energy shift induced by the dielectric inhomogeneity and
temperature itself remains larger than the broadening of the plasmon energy
dispersions due to the Landau damping. The obtained new features of the plasmon
dispersions can be observed in frictional drag measurements and in inelastic
light scattering and electron energy-loss spectroscopies.Comment: 5 pages, 3 figure
Response properties of III-V dilute magnetic semiconductors: interplay of disorder, dynamical electron-electron interactions and band-structure effects
A theory of the electronic response in spin and charge disordered media is
developed with the particular aim to describe III-V dilute magnetic
semiconductors like GaMnAs. The theory combines a detailed k.p description of
the valence band, in which the itinerant carriers are assumed to reside, with
first-principles calculations of disorder contributions using an
equation-of-motion approach for the current response function. A fully dynamic
treatment of electron-electron interaction is achieved by means of
time-dependent density functional theory. It is found that collective
excitations within the valence band significantly increase the carrier
relaxation rate by providing effective channels for momentum relaxation. This
modification of the relaxation rate, however, only has a minor impact on the
infrared optical conductivity in GaMnAs, which is mostly determined by the
details of the valence band structure and found to be in agreement with
experiment.Comment: 15 pages, 9 figure
Pattern formation in systems with competing interactions
There is a growing interest, inspired by advances in technology, in the low
temperature physics of thin films. These quasi-2D systems show a wide range of
ordering effects including formation of striped states, reorientation
transitions, bubble formation in strong magnetic fields, etc. The origins of
these phenomena are, in many cases, traced to competition between short ranged
exchange ferromagnetic interactions, favoring a homogeneous ordered state, and
the long ranged dipole-dipole interaction, which opposes such ordering on the
scale of the whole sample. The present theoretical understanding of these
phenomena is based on a combination of variational methods and a variety of
approximations, e.g., mean-field and spin-wave theory. The comparison between
the predictions of these approximate methods and the results of MonteCarlo
simulations are often difficult because of the slow relaxation dynamics
associated with the long-range nature of the dipole-dipole interactions. In
this note we will review recent work where we prove existence of periodic
structures in some lattice and continuum model systems with competing
interactions. The continuum models have also been used to describe
micromagnets, diblock polymers, etc.Comment: 11 pages, 1 figure, to appear in the AIP conference proceedings of
the 10th Granada Seminar on Computational Physics, Sept. 15-19, 2008. (v2)
Updated reference
Recurrence Quantification Analysis and Principal Components in the Detection of Short Complex Signals
Recurrence plots were introduced to help aid the detection of signals in
complicated data series. This effort was furthered by the quantification of
recurrence plot elements. We now demonstrate the utility of combining
recurrence quantification analysis with principal components analysis to allow
for a probabilistic evaluation for the presence of deterministic signals in
relatively short data lengths.Comment: 10 pages, 3 figures; Elsevier preprint, elsart style; programs used
for analysis available for download at http://homepages.luc.edu/~cwebbe
Anomalous spin-resolved point-contact transmission of holes due to cubic Rashba spin-orbit coupling
Evidence is presented for the finite wave vector crossing of the two lowest
one-dimensional spin-split subbands in quantum point contacts fabricated from
two-dimensional hole gases with strong spin-orbit interaction. This phenomenon
offers an elegant explanation for the anomalous sign of the spin polarization
filtered by a point contact, as observed in magnetic focusing experiments.
Anticrossing is introduced by a magnetic field parallel to the channel or an
asymmetric potential transverse to it. Controlling the magnitude of the
spin-splitting affords a novel mechanism for inverting the sign of the spin
polarization.Comment: 4 pages, 3 figure
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