1,814 research outputs found
Asymptotics of a Class of Solutions to the Cylindrical Toda Equations
The small t asymptotics of a class of solutions to the 2D cylindrical Toda
equations is computed. The solutions, q_k(t), have the representation q_k(t) =
log det(I-lambda K_k) - log det(I-lambda K_{k-1}) where K_k are integral
operators. This class includes the n-periodic cylindrical Toda equations. For
n=2 our results reduce to the previously computed asymptotics of the 2D radial
sinh-Gordon equation and for n=3 (and with an additional symmetry contraint)
they reduce to earlier results for the radial Bullough-Dodd equation.Comment: 29 pages, no figures, LaTeX fil
Entanglement scaling in critical two-dimensional fermionic and bosonic systems
We relate the reduced density matrices of quadratic bosonic and fermionic
models to their Green's function matrices in a unified way and calculate the
scaling of bipartite entanglement of finite systems in an infinite universe
exactly. For critical fermionic 2D systems at T=0, two regimes of scaling are
identified: generically, we find a logarithmic correction to the area law with
a prefactor dependence on the chemical potential that confirms earlier
predictions based on the Widom conjecture. If, however, the Fermi surface of
the critical system is zero-dimensional, we find an area law with a
sublogarithmic correction. For a critical bosonic 2D array of coupled
oscillators at T=0, our results show that entanglement follows the area law
without corrections.Comment: 4 pages, 4 figure
Inelastic Effects in Low-Energy Electron Reflectivity of Two-dimensional Materials
A simple method is proposed for inclusion of inelastic effects (electron
absorption) in computations of low-energy electron reflectivity (LEER) spectra.
The theoretical spectra are formulated by matching of electron wavefunctions
obtained from first-principles computations in a repeated vacuum-slab-vacuum
geometry. Inelastic effects are included by allowing these states to decay in
time in accordance with an imaginary term in the potential of the slab, and by
mixing of the slab states in accordance with the same type of distribution as
occurs in a free-electron model. LEER spectra are computed for various
two-dimensional materials, including free-standing multilayer graphene,
graphene on copper substrates, and hexagonal boron nitride (h-BN) on cobalt
substrates.Comment: 21 pages, 7 figure
Converse Magnetoelectric Experiments on a Room Temperature Spirally Ordered Hexaferrite
Experiments have been performed to measure magnetoelectric properties of room
temperature spirally ordered Sr3Co2Fe24O41 hexaferrite slabs. The measured
properties include the magnetic permeability, the magnetization and the strain
all as a function of the electric field E and the magnetic intensity H. The
material hexaferrite Sr3Co2Fe24O41 exhibits broken symmetries for both time
reversal and parity. The product of the two symmetries remains unbroken. This
is the central feature of these magnetoelectric materials. A simple physical
model is proposed to explain the magnetoelectric effect in these materials.Comment: 6 pages, 5 figure
Magnetoelectric Effects on Composite Nano Granular Films
Employing a new experimental technique to measure magnetoelectric response
functions, we have measured the magnetoelectric effect in composite films of
nano granular metallic iron in anatase titanium dioxide at temperatures below
50 K. A magnetoelectric resistance is defined as the ratio of a transverse
voltage to bias current as a function of the magnetic field. In contrast to the
anomalous Hall resistance measured above 50 K, the magnetoelectic resistance
below 50 K is significantly larger and exhibits an even symmetry with respect
to magnetic field reversal . The measurement technique required
attached electrodes in the plane of the film composite in order to measure
voltage as a function of bias current and external magnetic field. To our
knowledge, the composite films are unique in terms of showing magnetoelectric
effects at low temperatures, 50 K, and anomalous Hall effects at high
temperatures, 50 K.Comment: ReVTeX, 2 figures, 3 page
First-principles prediction of a decagonal quasicrystal containing boron
We interpret experimentally known B-Mg-Ru crystals as quasicrystal
approximants. These approximant structures imply a deterministic decoration of
tiles by atoms that can be extended quasiperiodically. Experimentally observed
structural disorder corresponds to phason (tile flip) fluctuations.
First-principles total energy calculations reveal that many distinct tilings
lie close to stability at low temperatures. Transfer matrix calculations based
on these energies suggest a phase transition from a crystalline state at low
temperatures to a high temperature state characterized by tile fluctuations. We
predict BMgRu forms a decagonal quasicrystal that is
metastable at low temperatures and may be thermodynamically stable at high
temperatures.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let
Phason elasticity of a three-dimensional quasicrystal: transfer-matrix method
We introduce a new transfer matrix method for calculating the thermodynamic
properties of random-tiling models of quasicrystals in any number of
dimensions, and describe how it may be used to calculate the phason elastic
properties of these models, which are related to experimental measurables such
as phason Debye-Waller factors, and diffuse scattering wings near Bragg peaks.
We apply our method to the canonical-cell model of the icosahedral phase,
making use of results from a previously-presented calculation in which the
possible structures for this model under specific periodic boundary conditions
were cataloged using a computational technique. We give results for the
configurational entropy density and the two fundamental elastic constants for a
range of system sizes. The method is general enough allow a similar calculation
to be performed for any other random tiling model.Comment: 38 pages, 3 PostScript figures, self-expanding uuencoded compressed
tar file, LaTeX using RevTeX macros and epsfig.st
On the Distribution of a Second Class Particle in the Asymmetric Simple Exclusion Process
We give an exact expression for the distribution of the position X(t) of a
single second class particle in the asymmetric simple exclusion process (ASEP)
where initially the second class particle is located at the origin and the
first class particles occupy the sites {1,2,...}
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