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astro-ph/9206004
|
Dynamics of the Intermediate-Age Elliptical LMC Cluster NGC 1978
|
In this paper we investigate the internal dynamics of the LMC cluster NGC
1978 through the use of Photometric (CCD images) and kinematic (stellar radial
velocities) data. We apply a variety of dynamical models to this data,
including multi-mass King-Michie models and rotating and non-rotating oblate
spheroid models. We discuss the cluster mass-to-light ratio and place
constraints on the cluster mass function.
| 1992-06-23
| 2009-10-22
|
[
"astro-ph"
] |
Philippe Fischer, Douglas L. Welch, and Mario Mateo
|
astro-ph/9206003
|
Gamma Ray Signatures from Ordinary Cosmic Strings
|
We calculate the flux of ultra high energy photons from individual ordinary
(i.e. non-superconducting) cosmic strings and compare the results with the
sensitivity of current and proposed TeV and EeV telescopes. Our calculations
give only upper limits for the gamma ray flux, since the source of the photons,
jets from particle production at cusps, may be weakened by back reaction
effects. For the usual cosmic distribution of strings, the predicted bursts
from strings with the value of mass per unit length associated with galaxy
formation or light strings may just be detectable. A diffuse gamma ray
background from light strings may also be seen by the Fly's Eye detector at
above $7 \times 10^{10}$ GeV.
| 1992-06-19
| 2009-10-22
|
[
"astro-ph",
"hep-ph"
] |
Jane H. MacGibbon (NASA/Goddard) and Robert H. Brandenberger (Brown)
|
astro-ph/9206002
|
Primordial Nucleosynthesis and the Abundances of Beryllium and Boron
|
The ability to now make measurements of Be and B as well as put constraints
on \lisix\ abundances in metal-poor stars has led to a detailed reexamination
of Big Bang Nucleosynthesis in the $A\groughly6$ regime. The nuclear reaction
network has been significantly expanded with many new rates added. It is
demonstrated that although a number of $A>7$ reaction rates are poorly
determined, even with extreme values chosen, the standard homogeneous model is
unable to produce significant yields (Be/H and B/H $<10^{-17}$ when $A\le7$
abundances fit) above $A=7$ and the \liseven/\lisix\ ratio always exceeds 500.
We also preliminarily explore inhomogeneous models, such as those inspired by a
first order quark-hadron phase transition, where regions with high
neutron/proton ratios can allow some leakage up to $A>7$. However models that
fit the $A\le7$ abundances still seem to have difficulty in obtaining
significant $A>7$ yields.
| 1992-06-18
| 2009-09-15
|
[
"astro-ph"
] |
David Thomas, David N. Schramm, Keith A. Olive, Brian D. Fields
|
astro-ph/9206001
|
Electroweak Baryogenesis with Electroweak Strings
|
If stable electroweak strings are copiously produced during the electroweak
phase transition, they may contribute significantly to the presently observed
baryon to entropy ratio of the Universe. This analysis establishes the
feasibility of implementing an electroweak baryogenesis scenario without a
first order phase transition.
| 1992-06-16
| 2010-11-01
|
[
"astro-ph",
"hep-ph"
] |
Robert H. Brandenberger (Brown) and Anne-Christine Davis (DAMTP,
Cambridge)
|
astro-ph/9205006
|
Can the Quark-Gluon Plasma in the Early Universe be supercooled?
|
The quark-hadron phase transition in the early universe can produce
inhomogeneities in the distribution of nucleons, which in turn affect the
primordial nucleosynthesis. In all the investigations of this problem it has
been assumed that the degree of supercooling of the quark-gluon plasma after
the phase transition is large enough to produce a significant rate of
nucleation of hadrons. Using the latest results of finite temperature lattice
QCD and the finite size scaling theory, we argue that the degree of
supercooling is in fact extremely small and hence the nucleation rate is
negligible.
| 1992-05-13
| 2009-10-22
|
[
"astro-ph",
"hep-lat"
] |
B. Banerjee and R. V. Gavai
|
astro-ph/9205005
|
Chaotic Dark Matter
|
A very weakly coupled scalar field with mass $m$ and initial vacuum
expectation value $V$ will provide enough mass to close the universe provided
$V\simeq (3\times 10^8\gev)(100\gev/m)^{1/4}$. We discuss possible models in
which such a field could arise.
| 1992-05-09
| 2009-10-22
|
[
"astro-ph"
] |
R. Rangarajan and M. Srednicki
|
astro-ph/9205004
|
The Spatial Distribution of Nearby Galaxy Clusters in the Northern and
Southern Galactic Hemispheres
|
We compare the spatial distributions of galaxy clusters in the northern and
southern galactic hemispheres, and the Abell and ACO clusters distributions. We
perform a statistical (correlation and cluster) analysis of a sample of Abell
and ACO galaxy clusters in the southern galactic hemisphere. We compare these
results with a symmetric sample at northern galactic latitude taken from
Postman et al. (1992). For the northern sample, we substantially confirm the
results of Postman et al. We find that the two-point spatial correlation
function of northern and southern clusters is comparable, with mean correlation
length 19.6 Mpc and slope -1.8 positive up to about 45 Mpc. Percolation
properties are remarkably similar in the northern and southern cluster samples.
We give also a catalog of superclusters. In the south galactic hemisphere the
main feature is a very rich, extended supercluster in the Horologium region at
a redshift 0.06, near to a large void.
| 1992-05-08
| 2011-05-23
|
[
"astro-ph"
] |
A. Cappi & S. Maurogordato
|
astro-ph/9205003
|
Particle Acceleration in (by) Accretion Discs
|
I present a model for acceleration of protons by the second-order Fermi
process acting on randomly scrambled magnetic flux arches above an accretion
disc. The accelerated protons collide with thermal protons in the disc,
producing degraded energetic protons, charged and neutral pions, and neutrons.
The pions produce gamma-rays by spontaneous decay of $\pi^0$ and by
bremsstrahlung and Compton processes following the decay of $\pi^\pm$ to
$e^\pm$.
| 1992-05-04
| 2009-10-22
|
[
"astro-ph"
] |
J. I. Katz
|
astro-ph/9205002
|
Giant Molecular Cloud Formation through the Parker Instability in a
Skewed Magnetic Field
|
The effect of the magnetic skew on the Parker instability is investigated by
means of the linear stability analysis for a gravitationally stratified gas
layer permeated by a horizontal magnetic field. When the magnetic field is
skewed (i.e., the field line direction is a function of the height), the
wavelength of the most unstable mode is $ \lambda \; \sim \; 10 H $ where $ H $
is the pressure scale height. The growth rate of the short wavelength modes is
greatly reduced when the gradient in the magnetic field direction exceeds 0.5
radian per scale height. Our results indicate that the Parker instability in a
skewed magnetic field preferentially forms large scale structures like giant
molecular clouds.
| 1992-05-02
| 2009-10-22
|
[
"astro-ph"
] |
T. Hanawa, R. Matsumoto and K. Shibata
|
astro-ph/9205001
|
Nonstationary Gravitational Lenses and the Fermat Principle
|
We apply Perlick's (1990a) rigorous formulation of the Fermat principle in
arbitrary spacetimes to prove the correctness of the description of
gravitational lensing by gravitational waves, given in the literature using the
scalar and vector formalisms. We obtain an expression for the time delay due to
such nonstationary lenses; the advantage over previous papers is that Perlick's
formulation of the Fermat principle is very rigorous and more suitable for
practical calculations in some cases. It is also shown that ordinary moving
gravitational lenses must be considered as a stationary case.
| 1992-05-01
| 2011-07-19
|
[
"astro-ph"
] |
Valerio Faraoni
|
astro-ph/9204006
|
Nova Dust Nucleation: Kinetics and Photodissociation
|
Dust is observed to form in nova ejecta. The grain temperature is determined
by the diluted nova radiation field rather than the gas kinetic temperature,
making classical nucleation theory inapplicable. We used kinetic equations to
calculate the growth of carbon nuclei in these ejecta. For expected values of
the parameters too many clusters grew, despite the small sticking probability
of atoms to small clusters, and the clusters only reached radii of about
100\AA\ when the carbon vapor was depleted. We then included the effects of
cluster photodissociation by ultraviolet radiation from the nova. This
suppresses nucleation, but too well, and no grains form at all. Finally we
suggest that a few growing carbon nuclei may be protected from
photodissociation by a sacrificial surface layer of hydrogen.
| 1992-04-30
| 2009-10-22
|
[
"astro-ph"
] |
D. J. Johnson, M. W. Friedlander, J. I. Katz
|
astro-ph/9204005
|
Radiation Transfer in Gamma-Ray Bursts
|
We have calculated gamma-ray radiative transport in regions of high energy
density, such as gamma-ray burst source regions, using a discrete ordinate,
discrete energy group method. The calculations include two-photon pair
production and annihilation, as well as three-photon pair annihilation. The
radiation field itself acts as an absorbing medium, and the optical depth
depends on its intensity, so the problem is intrinsically nonlinear. Spherical
divergence produces effective collimation of the flux. At high optical depth
the high energy ($E > 1$ MeV) portion of the emergent spectrum assumes a nearly
universal form. An approximate limit is derived for the high energy flux from a
gamma-ray burst source region of given size, and the implications of this limit
for the distance to the March 5, 1979 event are briefly discussed. We discuss
more generally the problem of very luminous bursts, and implications of
Galactic halo distances for flare models.
| 1992-04-30
| 2009-10-22
|
[
"astro-ph"
] |
B. J. Carrigan and J. I. Katz
|
astro-ph/9204004
|
Expanding Photospheres of Type II Supernovae and the Extragalactic
Distance Scale
|
We use the Expanding Photosphere Method to determine distances to 10 type II
supernovae. The effects of asymmetries, extinction, and flux dilution are
explored. Using empirical evidence and time-independent, spherical models which
treat H and He in non-LTE, we show that blackbody corrections caused by flux
dilution are small for type II supernovae in the infrared, and in the optical
when their color temperatures are less than 6000~K. The extinction to a type
II-P supernova can be estimated from its light curve: the uncertainty
introduced into a distance measurement due to extinction is usually less than
10\%. Correcting for extinction and flux dilution we derive distances to 10
supernovae: SN 1968L, SN 1969L, SN 1970G, SN 1973R, SN 1979C, SN 1980K, SN
1987A, SN 1988A, SN 1990E, and SN 1990ae. The distance measurements span a wide
range, 50 kpc to 120 Mpc, which is unique among the methods for establishing
the extragalactic distance scale. The distances measured to SN 1970G in M101
and SN 1987A in the LMC are in good agreement with distances determined from
Cepheid variable stars. Our distance to the Virgo Cluster, 22 +- 3 Mpc, is
larger than recent distances estimates made using surface brightness
fluctuations, planetary nebula luminosity functions, and the Tully-Fisher
method. Using the distances determined from these type II supernovae we derive
a value of $H_0 = 60 \pm 10$ km sec$^{-1}$Mpc$^{-1}$. This value is subject to
errors caused by local deviations in the Hubble flow, but will soon be improved
by applying the Expanding Photosphere Method to several distant type II
supernovae.
| 1992-04-30
| 2009-10-22
|
[
"astro-ph"
] |
B P Schmidt, R P Kirshner, R G Eastman
|
astro-ph/9204003
|
The Ptolemaic Gamma-Ray Burst Universe
|
The BATSE experiment on GRO has demonstrated the isotropic arrival directions
and flat $\log N$ {\it vs.} $\log S$ of cosmic gamma-ray bursts. These data are
best explained if the burst sources are distributed throughout an extended
spherical Galactic halo, as previously suggested by Jennings. The halo's radius
is at least 40 Kpc, and probably is more than 100 Kpc. I consider possible
origins of this halo, including primordial formation and neutron stars
recoiling from their birthplaces in the Galactic disc. A simple geometrical
model leads to a predicted relation between the dipole and quadrupole
anisotropy. I suggest that neutron stars born with low recoil become
millisecond pulsars, while those born with high recoil become the sources of
gamma-ray bursts; these populations are nearly disjoint. Quiescent counterparts
of gamma-ray bursts are predicted to be undetectably faint.
| 1992-04-29
| 2009-10-22
|
[
"astro-ph"
] |
J. I. Katz
|
astro-ph/9204002
|
Gravitational Lensing and the Variability of G
|
The four observables associated with gravitational lensing of distant quasars
by intervening galaxies: image splittings, relative amplifications, time
delays, and optical depths, provide separate measures of the strength of the
gravitational constant $G$ at cosmological distances. These allow one, in
principle, to factor out unknown lensing parameters to directly to probe the
variation of $G$ over cosmological time. We estimate constraints on $\dot{G}$
which may be derivable by this method both now and in the future. The limits
one may obtain can compete or exceed other direct limits on $\dot{G}$ today,
but unfortunately extracting this information, is not independent of the effort
to fix other cosmological parameters such as $H_0$ and $\Omega_0$ from lensing
observations.
| 1992-04-26
| 2009-08-18
|
[
"astro-ph"
] |
Lawrence Krauss and Martin White
|
astro-ph/9204001
|
Gamma-Ray Bursts as the Death Throes of Massive Binary Stars
|
It is proposed that gamma-ray bursts are created in the mergers of double
neutron star binaries and black hole neutron star binaries at cosmological
distances. Bursts with complex profiles and relatively long durations are the
result of magnetic flares generated by the Parker instability in a post-merger
differentially-rotating disk. Some bursts may also be produced through
neutrino-antineutrino annihilation into electrons and positrons. In both cases,
an optically thick fireball of size $\sles\ 100$ km is initially created, which
expands ultrarelativistically to large radii before radiating. Several previous
objections to the cosmological merger model are eliminated. It is predicted
that $\gamma$-ray bursts will be accompanied by a burst of gravitational
radiation from the spiraling-in binary which could be detected by LIGO.
| 1992-04-13
| 2009-10-22
|
[
"astro-ph"
] |
Ramesh Narayan, Bohdan Paczy\'nski, and Tsvi Piran
|
cond-mat/9212036
|
Dimerization structures on the metallic and semiconducting fullerene
tubules
|
The Kekule patterns are realized in the metallic tubules and chain-like
distortions occur in the semiconducting tubules.
| 1992-12-31
| 2007-05-23
|
[
"cond-mat"
] |
Kikuo Harigaya (1) and Mitsutaka Fujita (2) ((1)Department of Physics,
University of Sheffield, United Kingdom, (2) Institute of Materials Science,
University of Tsukuba, Japan)
|
cond-mat/9212035
|
On flux phase and N\'eel antiferromagnetism in the {\em t}-{\em
J}-model}}
|
We reanalyse the mathematical formulation of the flux-state problem within
the $t$-$J$ model. The analysis of different parametrizations in the functional
representation shows that (i) calculations which take into account constraints
for the number of on-site-available states are describing quasiparticles in
terms of wrong local statistics, and contain gauge non-invariant objects; (ii)
application of the projection technique in the slave-boson(fermion)
representation reproduces the correct statistics, and is exactly equivalent to
the conventional diagram technique for Hubbard operators; (iii) it is necessary
to introduce an additional equation for the effective hopping amplitude for the
flux phase. With the technique for Hubbard operators, which allows one to
separate charge and spin channels we construct the mean-field equations for a
flux-like state which coexists with N\'eel antiferromagnetism (AF). The formal
analysis shows that the equations for real and imaginary parts of the effective
hopping amplitude are inconsistent for any $\theta \neq 0$ (including $\theta
=\pi /4$ which gives flux 1/2). The hopping amplitude is slightly supressed by
exchange renormalization. The N\'eel magnetization $m$ decreases with
increasing concentration of holes. The region where antiferromagnetism exists
is decreasing
| 1992-12-29
| 2007-05-23
|
[
"cond-mat"
] |
I.S. Sandalov, M. Richter
|
cond-mat/9212034
|
Hierarchical Wave Functions of Fractional Quantum Hall Effect on the
Torus
|
One kind of the hierarchical wave functions of Fractional Quantum Hall Effect
on the torus is constructed. We find that the wave functions closely relate to
the wave functions of generalized Abelian Chern-Simons theory.
| 1992-12-28
| 2008-11-26
|
[
"cond-mat",
"hep-th"
] |
Dingping Li
|
cond-mat/9212033
|
Hierarchical Wave Functions and Fractional Statistics in Fractional
Quantum Hall Effect on the Torus
|
One kind of hierarchical wave functions of Fractional Quantum Hall Effect
(FQHE) on the torus are constructed. The multi-component nature of anyon wave
functions and the degeneracy of FQHE on the torus are very clear reflected in
this kind of wave functions. We also calculate the braid statistics of the
quasiparticles in FQHE on the torus and show they fit to the picture of anyons
interacting with magnetic field on the torus obtained from braid group
analysis.
| 1992-12-28
| 2015-06-25
|
[
"cond-mat",
"hep-th"
] |
Dingping Li
|
cond-mat/9212032
|
Spatial Correlation of Conduction Electrons in Metal with Complicated
Geometry Of The Fermi Surface
|
The "density-density" correlation function of conduction electrons in metal
is investigated. It is shown, that the asymptotic behaviour of the CF depends
on the shape and the local geometry of the Fermi surface. In particular, the
exponent of power law which describes the damping of Friedel oscillations at
large r (-4 for an isotropic Fermi gas) is determined by local geometry of the
FS. The applications of the obtained results to calculations of the CF in a
metal near the electron topological transition and of the RKKY exchange
integral are considered as well.
| 1992-12-25
| 2009-10-22
|
[
"cond-mat"
] |
D.I.Golosov and M.I.Kaganov
|
cond-mat/9212031
|
Spin Gap and Superconductivity in the One-Dimensional t-J Model with
Coulomb Repulsion
|
The one-dimensional t-J model with density-density repulsive interactions is
investigated using exact diagonalization and quantum Monte Carlo methods. A
short-range repulsion pushes phase separation to larger values of J/t, and
leads to a widened precursor region in which a spin gap and strengthened
superconducting correlations appear. The correlation exponent is calculated. On
the contrary, a long-range repulsion of $1/r$-form suppresses superconductivity
in the precursor region.
| 1992-12-23
| 2007-05-23
|
[
"cond-mat"
] |
M.Troyer, H. Tsunetsugu, T.M. Rice, J. Riera and E. Dagotto
|
cond-mat/9212030
|
Gapless Spin-Fluid Ground State in a Random Quantum Heisenberg Magnet
|
We examine the spin-$S$ quantum Heisenberg magnet with Gaussian-random,
infinite-range exchange interactions. The quantum-disordered phase is accessed
by generalizing to $SU(M)$ symmetry and studying the large $M$ limit. For large
$S$ the ground state is a spin-glass, while quantum fluctuations produce a
spin-fluid state for small $S$. The spin-fluid phase is found to be generically
gapless - the average, zero temperature, local dynamic spin-susceptibility
obeys $\bar{\chi} (\omega ) \sim \log(1/|\omega|) + i (\pi/2) \mbox{sgn}
(\omega)$ at low frequencies. This form is identical to the phenomenological
`marginal' spectrum proposed by Varma {\em et. al.\/} for the doped cuprates.
| 1992-12-21
| 2009-01-23
|
[
"cond-mat"
] |
Subir Sachdev and Jinwu Ye
|
cond-mat/9212029
|
Super Lax Pairs and Infinite Symmetries in The $1/r^2$ System
|
We present an algebraic structure that provides an interesting and novel link between supersymmetry and quantum integrability. This structure underlies two classes of models that are exactly solvable in 1-dimension and belong to the $1/r^2 $ family of interactions. The algebra consists of the commutation between a ``Super- Hamiltonian'', and two other operators, in a Hilbert space that is an enlargement of the original one by introducing fermions. The commutation relations reduce to quantal Ordered Lax equations when projected to the original subspace, and to a statement about the ``Harmonic Lattice Potential'' structure of the Lax operator. These in turn lead to a highly automatic proof of the integrability of these models. In the case of the discrete $SU(n)-1/r^2$ model, the `` Super-Hamiltonian'' is again an $SU(m)-1/r^2$ model with a related $m$, providing an interesting hierarchy of models.
| 1992-12-19
| 2025-07-03
|
[
"cond-mat"
] |
B. Sriram Shastry (AT & T Bell Laboratories, Murray Hill, N.J.) and Bill Sutherland (Department of Physics, University of Utah, Salt Lake City)
|
cond-mat/9212028
|
Solution of Some Integrable One-Dimensional Quantum Systems
|
In this paper, we investigate a family of one-dimensional multi-component
quantum many-body systems. The interaction is an exchange interaction based on
the familiar family of integrable systems which includes the inverse square
potential. We show these systems to be integrable, and exploit this
integrability to completely determine the spectrum including degeneracy, and
thus the thermodynamics. The periodic inverse square case is worked out
explicitly. Next, we show that in the limit of strong interaction the "spin"
degrees of freedom decouple. Taking this limit for our example, we obtain a
complete solution to a lattice system introduced recently by Shastry, and
Haldane; our solution reproduces the numerical results. Finally, we emphasize
the simple explanation for the high multiplicities found in this model.
| 1992-12-18
| 2009-10-22
|
[
"cond-mat"
] |
Bill Sutherland, B. Sriram Shastry (Physics Department, AT&T Bell
Labs, Murray Hill, NJ and University of Utah, Salt Lake City, UT)
|
cond-mat/9212027
|
A Solvable Spin-Glass of Quantum Rotors
|
We examine a model of $M$-component quantum rotors coupled by
Gaussian-distributed random, infinite-range exchange interactions. A complete
solution is obtained at $M=\infty$ in the spin-glass and quantum-disordered
phases. The quantum phase transition separating them is found to possess
logarithmic violations of scaling, with no further modifications to the leading
critical behavior at any order in $1/M$; this suggests that the critical
properties of the transverse-field Ising model (believed to be identical to the
$M\rightarrow 1$ limit) are the same as those of the $M=\infty$ quantum rotors.
| 1992-12-18
| 2009-01-23
|
[
"cond-mat"
] |
Jinwu Ye, Subir Sachdev, and N. Read
|
cond-mat/9212025
|
Fractional Quantum Hall States in Narrow Channels
|
A model system is considered where two dimensional electrons are confined by
a harmonic potential in one direction, and are free in the other direction.
Ground state in strong magnetic fields is investigated through numerical
diagonalization of the Hamiltonian. It is shown that the fractional quantum
Hall states are realized even in the presence of the external potential under
suitable conditions, and a phase diagram is obtained.
| 1992-12-17
| 2009-10-22
|
[
"cond-mat"
] |
Daijiro Yoshioka
|
cond-mat/9212026
|
On Oscillations in Cellular Automata
|
We investigate cellular automata where some global quantity varies
periodically or quasiperiodically with time. We find that these systems are
highly predictable, and can be rather well described by a set of mean-field
variables. We conclude that this is not a collective phenomenon - where
different subsystems are supposed to synchronize - but rather like many very
weakly coupled oscillators fluctuating around one exact frequency. The global
quantity measured is a mean taken over all these subsystems, and gets more
precise the larger the system is.
| 1992-12-17
| 2009-10-22
|
[
"cond-mat"
] |
Jan Hemmingsson and Hans J. Herrmann
|
cond-mat/9212024
|
Multiscaling analysis and width of the active zone of large off-lattice
DLA
|
We measure the multiscaling behavior of large off-lattice diffusion limited
aggregates (DLA). In contrast to previous studies we now find a continuous
dependence of the multiscaling dimensions $D(x)$ on the relative distance
$x=r/R_g$ to the center of the cluster. This result agrees with measurements on
smaller clusters. Furthermore we report the multiscaling behavior and the
behavior of the width of the active zone of one very large off-lattice DLA
cluster with 50 million particles. Here we find a sharp drop of the
multiscaling dimensions for large $x$ instead of a continuous behavior.
| 1992-12-16
| 2009-10-22
|
[
"cond-mat"
] |
Peter Ossadnik
|
cond-mat/9212023
|
Scaling Exponents for Kinetic Roughening in Higher Dimensions
|
We discuss the results of extensive numerical simulations in order to
estimate the scaling exponents associated with kinetic roughening in higher
dimensions, up to d=7+1. To this end, we study the restricted solid - on -
solid growth model, for which we employ a novel fitting {\it ansatz} for the
spatially averaged height correlation function $\bar G(t) \sim t^{2\beta}$ to
estimate the scaling exponent $\beta$. Using this method, we present a
quantitative determination of $\beta$ in d=3+1 and 4+1 dimensions. To check the
consistency of these results, we also compute the interface width and determine
$\beta$ and $\chi$ from it independently. Our results are in disagreement with
all existing theories and conjectures, but in four dimensions they are in good
agreement with recent simulations of Forrest and Tang [{\it Phys. Rev. Lett.}
{\bf 64}:1405 (1990)] for a different growth model. Above five dimensions, we
use the time dependence of the width to obtain lower bound estimates for
$\beta$. Within the accuracy of our data, we find no indication of an upper
critical dimension up to d=7+1.
| 1992-12-16
| 2009-10-22
|
[
"cond-mat"
] |
T. Ala-Nissila, T. Hjelt, J. M. Kosterlitz, and O. Ven\"al\"ainen
|
cond-mat/9212022
|
Electronic interactions in fullerene spheres
|
The electron-phonon and Coulomb interactions inC$_{60}$, and larger fullerene
spheres are analyzed. The coupling between electrons and intramolecular
vibrations give corrections $\sim 1 - 10$ meV to the electronic energies for
C$_{60}$, and scales as $R^{-4}$ in larger molecules. The energies associated
with electrostatic interactions are of order $\sim 1 - 4$ eV, in C$_{60}$ and
scale as $R^{-1}$. Charged fullerenes show enhanced electron-phonon coupling,
$\sim 10$ meV, which scales as $R^{-2}$. Finally, it is argued that non only
C$_{60}^{-}$, but also C$_{60}^{--}$ are highly polarizable molecules. The
polarizabilities scale as $R^3$ and $R^4$, respectively. The role of this large
polarizability in mediating intermolecular interactions is also discussed.
| 1992-12-15
| 2009-10-22
|
[
"cond-mat"
] |
F. Guinea, J. Gonzalez and M.A. H. Vozmediano
|
cond-mat/9212021
|
Test of Conformal Invariance in One-Dimensional Quantum Liquid with
Long-Range Interaction
|
We numerically study the momentum distribution of one-dimensional Bose and
Fermi systems with long-range interaction $g/r^2$ for the ``special'' values
$g= -\frac{1}{2}, 0, 4$, singled out by random matrix theory. The critical
exponents are shown to be independent of density and in excellent agreement
with estimates obtained from $c=1$ conformal finite-size scaling analysis.
| 1992-12-15
| 2014-09-02
|
[
"cond-mat",
"hep-th"
] |
Rudolf A. R\"omer and Bill Sutherland
|
cond-mat/9212020
|
Spin-Wave Theory and Finite-Size Scaling for the Heisenberg
Antiferromagnet
|
Spin-wave perturbation theory for the Heisenberg antiferromagnet at zero
temperature is used to compute the finite-lattice corrections to the ground
state energy, the staggered magnetization and the energy gap. The dispersion
relation, the spin-wave velocity and the bulk ground state energy to order
$O(1/S^2)$ are also computed for the square lattice. The results agree very
well with the predictions of Neuberger and Ziman and Fisher.
| 1992-12-14
| 2009-10-22
|
[
"cond-mat"
] |
Zheng Weihong and C.J. Hamer
|
cond-mat/9212019
|
The $1/N$ Expansion and Spin Correlations in Constrained Wavefunctions
|
We develop a large-N expansion for Gutzwiller projected spin states. We
consider valence bonds singlets, constructed by Schwinger bosons or fermions,
which are variational ground states for quantum antiferromagnets. This
expansion is simpler than the familiar expansions of the quantum Heisenberg
model, and thus more instructive. The diagrammatic rules of this expansion
allow us to prove certain identities to all orders in 1/N. We derive the
on-site spin fluctuations sum rule for arbitrary N. We calculate the
correlations of the one dimensional Valence Bonds Solid states and the
Gutzwiller Projected Fermi Gas upto order 1/N. For the bosons case, we are
surprised to find that the mean field, the order 1/N and the exact correlations
are simply proportional. For the fermions case, the 1/N correction enhances the
zone edge singularity. The comparison of our leading order terms to known
results for N=2, enhances our understanding of large-N approximations in
general.
| 1992-12-14
| 2009-10-22
|
[
"cond-mat"
] |
Maxim Raykin (Physics Department, Boston University, Boston, USA) and
Assa Auerbach (Physics Department, Technion, Haifa, Israel and Physics
Department, Boston University, Boston, USA)
|
cond-mat/9212018
|
Spin Tunneling, Berry phases and Doped Antiferromagnets
|
Interference effects between Berry phase factors in spin tunneling systems
have been discussed in recent Letters by Loss, DiVincenzo and Grinstein and von
Delft and Henley. This Comment points out that Berry phases in spin tunneling
are important in another interesting case: the two dimensional doped
antiferromagnet. I show that the dispersion of a single hole in the t-J model
changes sign as $e^{2\pi s}$ where $s$ is the size of the spins. This provides
an interpretation of the numerical results for the $s=\half$ model, and a
prediction for other spin sizes.
| 1992-12-10
| 2009-10-22
|
[
"cond-mat"
] |
Assa Auerbach
|
cond-mat/9212015
|
Theory of Anisotropic Superexchange in Insulating Cuprates
|
Spin-orbit corrections to superexchange are calculated using the method of
Moriya [T.\ Moriya, {\it Phys.\ Rev.}~{\bf 120} 91, (1960)] for two of the
insulating parent compounds of the cuprate superconductors: (1)
La$_{2-x}$Nd$_x$CuO$_4$ where the CuO$_6$ octahedra forming each Cu-O layer are
tilted in staggered fashion about an axis which depends on $x$ and temperature;
and (2) YBa$_2$Cu$_3$O$_{6+x}$ ($x \alt 0.4$) where the Cu-O layers form
CuO$_2$-Y-CuO$_2$ bilayers in which the in-plane O$^{2-}$ ions are displaced
uniformly towards the Y$^{3+}$ layer. For (1) a simple formula is derived for
the weak ferromagnetic moment in each Cu-O layer as a function of the tilting
axis and magnitude. For (2) it is shown that the anisotropic corrections to
superexchange are different from what has previously been assumed. For the
correct spin Hamiltonian a classical N\'eel state in which the Cu spins are
lying in the plane is unstable in a single Cu-O layer, but when a bilayer is
considered there is a critical value of the interlayer exchange coupling which
stabilizes this state. For both cases (1) and (2) spin-wave spectra are
calculated and shown to compare favorably with experiment.
| 1992-12-09
| 2009-10-22
|
[
"cond-mat"
] |
N.E. Bonesteel
|
cond-mat/9212014
|
Dynamical Properties of a Haldane Gap Antiferromagnet
|
We study the dynamic spin correlation function of a spin one
antiferromagnetic chain with easy-plane single-ion anisotropy. We use exact
diagonalization by the Lancz\H os method for chains of lengths up to N=16
spins. We show that a single-mode approximation is an excellent description of
the dynamical properties. A variational calculation allows us to clarify the
nature of the excitations. The existence of a two-particle continuum near zero
wavevector is clearly seen both in finite-size effects and in the dynamical
structure factor. The recent neutron scattering experiments on the
quasi-one-dimensional antiferromagnet NENP are fully explained by our results.
| 1992-12-09
| 2009-10-22
|
[
"cond-mat",
"hep-lat"
] |
O. Golinelli, Th. Jolicoeur, R. Lacaze
|
cond-mat/9212012
|
Exact Correlation Function at the Lifshitz Points of the Spherical Model
|
The spin-spin correlation function of the spherical model being precisely at
an anisotropic Lifshitz point of arbitrary order is calculated exactly. The
results are in agreement with scaling. The scaling function is shown to be
universal. The direction-dependent long-range correlations may change from
ferromagnetic to antiferromagnetic behaviour and back as the dimension is
varied. The form of the scaling function is compared to predictions following
from local scale invariance for strongly anisotropic critical systems.
| 1992-12-09
| 2011-09-26
|
[
"cond-mat",
"hep-lat",
"hep-th",
"math-ph",
"math.MP"
] |
Laurent Frachebourg and Malte Henkel
|
cond-mat/9212013
|
Bosonic Mean Field Theory of the Spiral Phases of Heisenberg
Antiferromagnets on a Chain
|
We develop a novel bosonic mean field theory to describe the spiral phases of
a Heisenberg antiferromagnet on a one-dimensional chain, in terms of three
bosons at each site. The ground state is disordered and for large values of the
spin $S$, two different and exponentially small energy gaps are found. The
spin-spin correlation function is computed and is shown to decay exponentially
at large distances. Our mean field theory is also shown to be exact in a
large-$N$ generalization.
| 1992-12-09
| 2009-10-22
|
[
"cond-mat"
] |
Sumathi Rao and Diptiman Sen
|
cond-mat/9212017
|
Flux Pinning and Phase Transitions in Model High-Temperature
Superconductors with Columnar Defects
|
We calculate the degree of flux pinning by defects in model high-temperature
superconductors (HTSC's). The HTSC is modeled as a three-dimensional network of
resistively-shunted Josephson junctions in an external magnetic field,
corresponding to a HTSC in the extreme Type-II limit. Disorder is introduced
either by randomizing the coupling between grains (Model A disorder) or by
removing grains (Model B disorder). Three types of defects are considered:
point disorder, random line disorder, and periodic line disorder; but the
emphasis is on random line disorder. Static and dynamic properties of the
models are determined by Monte Carlo simulations and by solution of the
analogous coupled overdamped Josephson equations in the presence of thermal
noise. Random line defects considerably raise the superconducting transition
temperature T$_c(B)$, and increase the apparent critical current density
J$_c(B,T)$, in comparison to the defect-free crystal. They are more effective
in these respects than a comparable volume density of point defects, in
agreement with the experiments of Civale {\it et al}. Periodic line defects
commensurate with the flux lattice are found to raise T$_c(B)$ even more than
do random line defects. Random line defects are most effective when their
density approximately equals the flux density. Near T$_c(B)$, our static and
dynamic results appear consistent with the anisotropic Bose glass scaling
hypotheses of Nelson and Vinokur, but with possibly different critical indices:
| 1992-12-09
| 2009-10-22
|
[
"cond-mat"
] |
K. H. Lee, D. Stroud, and S. M. Girvin
|
cond-mat/9212016
|
Tunneling Conductance Between Parallel Two Dimensional Electron Systems
|
We derive and evaluate expressions for the low temperature {\it dc}
equilibrium tunneling conductance between parallel two-dimensional electron
systems. Our theory is based on a linear-response formalism and on
impurity-averaged perturbation theory. The disorder broadening of features in
the dependence of tunneling conductance on sheet densities and in-plane
magnetic field strengths is influenced both by the finite lifetime of electrons
within the wells and by non-momentum-conserving tunneling events. Disorder
vertex corrections are important only for weak in-plane magnetic fields and
strong interwell impurity-potential correlations. We comment on the basis of
our results on the possibility of using tunneling measurements to determine the
lifetime of electrons in the quantum wells.
| 1992-12-09
| 2009-10-22
|
[
"cond-mat"
] |
Lian Zheng and A.H. MacDonald
|
cond-mat/9212011
|
Translational Correlations in the Vortex Array at the Surface of a
Type-II Superconductor
|
We discuss the statistical mechanics of magnetic flux lines in a
finite-thickness slab of type-II superconductor. The long wavelength properties
of a flux-line liquid in a slab geometry are described by a hydrodynamic free
energy that incorporates the boundary conditions on the flux lines at the
sample's surface as a surface contribution to the free energy. Bulk and surface
weak disorder are modeled via Gaussian impurity potentials. This free energy is
used to evaluate the two-dimensional structure factor of the flux-line tips at
the sample surface. We find that surface interaction always dominates in
determining the decay of translational correlations in the asymptotic
long-wavelength limit. On the other hand, such large length scales have not
been probed by the decoration experiments. Our results indicate that the
translational correlations extracted from the analysis of the Bitter patterns
are indeed representative of behavior of flux lines in the bulk.
| 1992-12-08
| 2009-10-22
|
[
"cond-mat"
] |
M.C. Marchetti (Syracuse University) and D.R. Nelson (Harvard
University)
|
cond-mat/9212005
|
Length-scale competition in the damped sine-Gordon chain
|
It is shown that there are two different regimes for the damped sine-Gordon
chain driven by the spatio-temporal periodic force $\Gamma sin(\omega t - k_{n}
x)$ with a flat initial condition. For $\Gamma_{c}(n)$ to a translating {\em
2-breather} excitation from a state locked to the driver. For $\omega < k_{n}$,
the excitations of the system are the locked states with the phase velocity
$\omega/k_{n}$ in all the region of $\Gamma$ studied. In the first regime, the
frequency of the breathers is controlled by $\omega$, and the velocity of the
breathers, controlled by $k_{n}$, is shown to be the group velocity determined
from the linear dispersion relation for the sine-Gordon equation. A linear
stability analysis reveals that, in addition to two competing length-scales,
namely, the width of the breathers and the spatial period of the driving, there
is one more length-scale which plays an important role in controlling the
dynamics of the system at small driving. In the second regime the length-scale
$k_{n}$ controls the excitation. The above picture is further corroborated by
numerical nonlinear spectral analysis. An energy balance estimate is also
presented and shown to predict the critical value of $\Gamma$ in good agreement
with the numerics.
| 1992-12-07
| 2007-05-23
|
[
"cond-mat"
] |
David Cai (1), A.R. Bishop (1), and Angel Sanchez (1,2) ((1)
Theoretical Division and CNLS, Los Alamos National Laboratory, (2) Escuela
Politecnica Superior, Universidad Carlos III de Madrid)
|
cond-mat/9212010
|
Dynamical Properties of a Single Hole in an Antiferromagnet
|
A finite size scaling analysis of the spectral function and of the optical
conductivity of a single hole moving in an antiferromagnetic background is
performed. It is shown that both the low energy quasiparticle peak and the
broad higher energy structure are robust with increasing cluster size from
$4\times 4$ to $\sqrt{26}\times\sqrt{26}$ sites. In the abscence of spin
fluctuations, for most static or dynamical quantities saturation occurs when
the size exceeds a characteristic size $N_c(J_z)$. Typically, 16 and 26 site
clusters give reliable results for $J_z>0.75$ and $J_z>0.3$ respectively. The
hole optical mass is shown to be very large ($>20$) in agreement with the small
bandwidth. Due to the energy gap to flip a spin in the vicinity of a hole, a
small gap $\propto J_z$ separates the low energy delta-function from the rest
of the spectrum in the dynamical correlation functions. On the other hand, with
$J_\perp$ this gap seems to disappear with increasing system size as one would
expect since the spin waves are gapless in the thermodynamic limit. The large
momentum dependence of the quasiparticle weight in the isotropic case is
inconsistent with a string picture but agrees well with the self-consistent
Born approximation. An accurate estimation of the higher energy part of the
spectral functions of the t--J model can be made for momenta close to $(0,0)$
or $(\pi,\pi)$;
| 1992-12-07
| 2009-10-22
|
[
"cond-mat"
] |
Didier Poilblanc, Timothy Ziman, H.J. Schulz and Elbio Dagotto
|
cond-mat/9212008
|
Indications of d_{x^2 - y^2} Superconductivity in the Two Dimensional
t-J Model
|
Superconducting correlations in the two dimensional ${\rm t-J}$ model at zero
temperature are evaluated using numerical techniques. At the fermionic density
$\langle n \rangle \sim 1/2$, strong signals of $\dx2y2$ superconductivity were
observed in the ground state. These conclusions are based on a study of static
pairing correlations, the Meissner effect, flux quantization, and other
indicators of superconductivity. It is argued that these results can be
explained using a spin dimer ``liquid'' state. A phase diagram of the two
dimensional ${\rm t-J}$ model is presented.
| 1992-12-07
| 2009-10-22
|
[
"cond-mat"
] |
Elbio Dagotto and Jose Riera
|
cond-mat/9212007
|
Low Temperature Transport through a Quantum Dot: The Anderson Model out
of Equilibrium
|
NEC technical report 92-079-2-0077-1.
| 1992-12-07
| 2009-10-22
|
[
"cond-mat"
] |
Y. Meir, N. S. Wingreen and P. A. Lee
|
cond-mat/9212006
|
A determination of the low energy parameters of the 2-d Heisenberg
antiferromagnet
|
We perform numerical simulations of the 2-d antiferromagnetic quantum
Heisenberg model using an efficient cluster algorithm. Comparing the finite
size and finite temperature effects of various quantities with recent results
from chiral perturbation theory we are able to determine the low energy
parameters of the system very precisely. We find $e_0 = - 0.6693(1) J/a^2$ for
the ground state energy density, ${\cal M}_s = 0.3074(4)/a^2$ for the staggered
magnetization, $\hbar c = 1.68(1) J a$ for the spin wave velocity and $\rho_s =
0.186(4) J$ for the spin stiffness. Our results agree with experimental data
for the undoped precursor insulators of high-$T_c$ superconductors.
| 1992-12-07
| 2007-05-23
|
[
"cond-mat",
"hep-lat"
] |
U.-J. Wiese and H.-P. Ying, (Bern University)
|
cond-mat/9212009
|
Basis Set Reduction Applied to the Two Dimensional t-Jz Model
|
A simple variation of the Lanczos method is discussed. The new technique is
based on a systematic reduction of the size of the Hilbert space of the model
under consideration. As an example, the two dimensional ${\rm t-J_z}$ model of
strongly correlated electrons is studied. Accurate results for the ground state
energy can be obtained on clusters of up to 50 sites, which are unreachable by
conventional Lanczos approaches. In particular, the energy of one and two holes
is analyzed as a function of ${\rm J_z/t}$. In the bulk limit, it is shown that
a finite coupling ${\rm J_z/t ]_c} \sim 0.18$ is necessary to induce
``binding'' of holes in the model. It is argued that this result implies that
the two dimensional ${\rm t-J}$ model phase separates only for couplings larger
than a $finite$ critical value.
| 1992-12-07
| 2009-10-22
|
[
"cond-mat"
] |
Jose Riera and Elbio Dagotto
|
cond-mat/9212004
|
Fractal Properties of the Distribution of Earthquake Hypocenters
|
We investigate a recent suggestion that the spatial distribution of
earthquake hypocenters makes a fractal set with a structure and fractal
dimensionality close to those of the backbone of critical percolation clusters,
by analyzing four different sets of data for the hypocenter distributions and
calculating the dynamical properties of the geometrical distribution such as
the spectral dimension $d_s$. We find that the value of $d_s$ is consistent
with that of the backbone, thus supporting further the identification of the
hypocenter distribution as having the structure of the percolation backbone.
| 1992-12-04
| 2009-10-22
|
[
"cond-mat"
] |
Hisao Nakanishi, Muhammad Sahimi, Michelle C. Robertson, Charles C.
Sammis and Mark D. Rintoul
|
cond-mat/9212003
|
Recurrent Clogging and Density Waves in Granular Material Flowing
through a Narrow Pipe
|
We report on density waves in granular material, investigated both
experimentally and numerically. When granular material falls through a long
narrow pipe one observes recurrent clogging. The kinetic energy of the falling
particles increases up to a characteristic threshold corresponding to the onset
of recurrent clogging and density waves of no definite wavelength. The
distances between regions of high density depend strongly on the initial
conditions. They vary irregularly without any characteristic time and length
scale. The particle-flow was investigated using 2D Molecular Dynamics
simulations. Experimental investigations lead to equivalent results.
| 1992-12-03
| 2007-05-23
|
[
"cond-mat",
"hep-lat"
] |
Thorsten Poeschel
|
cond-mat/9212002
|
Weak-Localization and Integrability in Ballistic Cavities
|
We demonstrate the existence of an interference contribution to the average
magnetoconductance, G(B), of ballistic cavities and use it to test the
semiclassical theory of quantum billiards. G(B) is qualitatively different for
chaotic and regular cavities, an effect explained semiclassically by the
differing classical distribution of areas. The magnitude of G(B) is poorly
explained by the semiclassical theory of coherent backscattering (elastic
enhancement factor)-- correlations beyond time-reversed pairs of trajectories
must be included-- but is in agreement with random matrix theory.
| 1992-12-02
| 2009-01-23
|
[
"cond-mat"
] |
H. U. Baranger, R. A. Jalabert, and A. D. Stone
|
cond-mat/9212001
|
The Mass Gap of the Nonlinear Sigma Model through the Finite Temperature
Effective Action
|
The $O(3)$ nonlinear $\sigma$ model is studied in the disordered phase, using
the techniques of the effective action and finite temperature field theory. The
nonlinear constraint is implemented through a Lagrange multiplier. The finite
temperature effective potential for this multiplier is calculated at one loop.
The existence of a nontrivial minimum for this potential is the signal of a
disordered phase in which the lowest excited state is a massive triplet. The
mass gap is easily calculated as a function of temperature in dimensions 1, 2
and 3. In dimension 1, this gap is known as the Haldane gap, and its
temperature dependence is compared with experimental results.
| 1992-12-01
| 2009-10-22
|
[
"cond-mat"
] |
D. Senechal
|
cond-mat/9211021
|
Magnetic Oscillations of a Fractional Hall Dot
|
We show that a quantum dot in the fractional Hall regime exhibits mesoscopic
magnetic oscillations with a period which is a multiple of the period for free
electrons. Our calculations are performed for parabolic quantum dots with
hard-core electron-electron interactions and are exact in the strong field
limit for $k_B T$ smaller than the fractional Hall gap. Explicit expressions
are given for the temperature dependence of the amplitude of the oscillations.
| 1992-11-30
| 2009-10-22
|
[
"cond-mat"
] |
A.H.MacDonald and M.D. Johnson
|
cond-mat/9211020
|
Diffusion and spectral dimension on Eden tree
|
We calculate the eigenspectrum of random walks on the Eden tree in two and
three dimensions. From this, we calculate the spectral dimension $d_s$ and the
walk dimension $d_w$ and test the scaling relation $d_s = 2d_f/d_w$ ($=2d/d_w$
for an Eden tree). Finite-size induced crossovers are observed, whereby the
system crosses over from a short-time regime where this relation is violated
(particularly in two dimensions) to a long-time regime where the behavior
appears to be complicated and dependent on dimension even qualitatively.
| 1992-11-27
| 2009-10-22
|
[
"cond-mat"
] |
Hisao Nakanishi and Hans J. Herrmann
|
cond-mat/9211019
|
Quantum Mechanics and Superconductivity in a Magnetic Field
|
The influence of a magnetic field on superconductivity is usually described
either phenomenologically, using Ginzburg-Landau theory, or semiclassically
using Gor'kov theory. In this article we discuss the influence of magnetic
fields on the mean-field theory of the superconducting instability from a
completely quantum mechanical point of view. The suppression of
superconductivity by an external magnetic field is seen in this more physically
direct picture to be due to the impossibility, in quantum mechanics, of
precisely specifying both the center-of-mass state of a pair and the individual
electron kinetic energies. We also discuss the possibility of novel aspects of
superconductivity at extremely strong magnetic fields where recent work has
shown that the transition temperature may be enhanced rather than suppressed by
a magnetic field and where a quantum treatment is essential.
| 1992-11-25
| 2015-06-25
|
[
"cond-mat"
] |
A. H. MacDonald, Hiroshi Akera and M.R. Norman
|
cond-mat/9211018
|
I-V Characteristics of High Temperature Superconductors with Columnar
Defects
|
The vortex glass transition in the presence of columnar defects is studied by
Monte Carlo simulations of a vortex loop model, suggested by the analogy to the
$T=0$ superconductor-insulator transition for dirty bosons in (2+1)D. From
finite-size scaling analysis of the $I$-$V$ characteristic we find two
dynamical exponents describing the non-equilibrium behavior. We obtain
$z_{\perp} = 6 \pm 0.5$ and $z_{\parallel} = 4 \pm 0.5$ when the current is
applied perpendicular and parallel to the columnar defects respectively.
| 1992-11-24
| 2009-10-22
|
[
"cond-mat"
] |
M. Wallin and S. M. Girvin
|
cond-mat/9211017
|
Possible Quantum Spin Liquid States on the Triangular and Kagome
Lattices
|
The frustrated spin-one-half Heisenberg model on triangualr and Kagome
Lattices is mapped onto a single specis of fermion carrying statistical flux.
The corresponding Chern-Simons gauge theory is analyzed at the Gaussian level
and found to be massive. This provides a new motivation for the spin-liquid
Kalmeyer-Laughlin wave function. Good overlap of this wave function with the
numerical ground state is found for small clusters.
| 1992-11-24
| 2016-08-31
|
[
"cond-mat"
] |
Kun Yang, K. L. Warman, and S. M. Girvin
|
cond-mat/9211016
|
Angle of Repose and Angle of Marginal Stability: Molecular Dyanmics of
Granular Particles
|
We present an implementation of realistic static friction in molecular
dynamics (MD) simulations of granular particles. In our model, to break
contacts between two particles, one has to apply a finite amount of force,
determined by the Coulomb criterion. Using a two dimensional model, we show
that piles generated by avalanches have a {\it finite} angle of repose
$\theta_R$ (finite slopes). Furthermore, these piles are stable under tilting
by an angle smaller than a non-zero tilting angle $\theta_T$, showing that
$\theta_R$ is different from the angle of marginal stability $\theta_{MS}$,
which is the maximum angle of stable piles. These measured angles are compared
to a theoretical approximation. We also measure $\theta_{MS}$ by continuously
adding particles on the top of a stable pile.
| 1992-11-23
| 2009-10-22
|
[
"cond-mat"
] |
Jysoo Lee and Hans J. Herrmann
|
cond-mat/9211015
|
Cellular automaton for the fracture of disordered media
|
We study numerically the growth of a crack in an elastic medium under the
influence of a travelling shockwave. We describe the implementation of a fast
algorithm which is perfectly suited for a data parallel computer. Using large
scale simulations on the Connection Machine we generate cracks with more than
10000 sites on a $\scriptstyle 1024 \times 1024$ lattice. We show that the
resulting patterns are fractal with a fractal dimension that depends on the
chosen breaking criterion and varies between $\scriptstyle 1.$ and
$\scriptstyle 2.$
| 1992-11-21
| 2015-06-25
|
[
"cond-mat"
] |
Peter Ossadnik
|
cond-mat/9211014
|
Spin-Peierls ground states and frustration in a multi-band
Peierls-Hubbard model
|
We discuss the consequences of including both electron-phonon and
electron-electron couplings in multi-band models, focusing on numerical studies
of a one-dimensional two-band model in the intermediate regime for both
coupling strengths. Spin-Peierls as well as long-period, frustrated ground
states are identified, reminisent of those found in antiferromagnetic
next-nearest neighbor (ANNNI) models. We speculate on experimentally observable
signatures of this rich phase diagram. 1992 PACS: 75.30.Fv, 71.45.Lr, 71.38+i,
64.70.Rh
| 1992-11-21
| 2009-10-22
|
[
"cond-mat"
] |
H. Roeder, A.R. Bishop, and J. Tinka Gammel
|
cond-mat/9211012
|
Second-Order Dynamics in the Collective Evolution of Coupled Maps and
Automata
|
We review recent numerical studies and the phenomenology of spatially
synchronized collective states in many-body dynamical systems. These states
exhibit thermodynamic noise superimposed on the collective, quasiperiodic order
parameter evolution with typically one basic irrational frequency. We
concentrate on the description of the global temporal properties in terms of
second-order difference equations.
| 1992-11-20
| 2014-10-13
|
[
"cond-mat",
"hep-lat"
] |
P.-M. Binder, V. Privman
|
cond-mat/9211013
|
Granular Material Flowing Down an Inclined Chute: A Molecular Dynamics
Simulation
|
Two-dimensional Molecular Dynamics simulations are used to model the free
surface flow of spheres falling down an inclined chute. The interaction between
the particles in our model is assumed to be subjected to the Hertzian contact
force and normal as well as shear friction. The stream of particles shows a
characteristic height profile, consisting of layers of different types of
fluidization. The numerically observed flow properties agree qualitatively with
experimental results.
| 1992-11-20
| 2009-10-22
|
[
"cond-mat",
"hep-lat"
] |
Thorsten Poeschel
|
cond-mat/9211011
|
On the Thermodynamics of Granular Media
|
A thermodynamic formulation for moving granular material is proposed. The
fluctuations due to the constant flux and dissipation of energy are controlled
in a `granular' ensemble by a pressure $\wp$ (`compression') which is conjugate
to a contact volume (`contactopy'). The corresponding response function
(`dissipativity') describes how dissipation increases with $\wp$ and should
serve to identify the fluidization transition and 1/f noise. In the granular
ensemble one can consider the granular medium as a gas of elastically colliding
particles and define a ``granular'' temperature and other standard
thermodynamic quantities. PACS: 05.70, 46.10
| 1992-11-18
| 2009-10-22
|
[
"cond-mat"
] |
H.J. Herrmann
|
cond-mat/9211010
|
The half-filled Hubbard model in the pair approximation of the Cluster
Variation Method
|
The half filled Hubbard model is studied in the pair approximation of the
Cluster Variation Method. The use of the $SO(4)$ symmetry of the model makes
possible to give a complete analytical characterization of the ground state, by
means of explicit expressions for the double occupancy and the nearest neighbor
correlation functions. The finite temperature analysis is reduced to the
numerical solution of only two coupled transcendental equations. The behavior
of local magnetic moment, specific heat and correlation functions is given for
some typical cases in one and two dimensions. We obtain good qualitative
agreement with exact and numerical results in one dimension. The results for
finite temperatures show a rapid evolution, with increasing temperature, from a
strongly antiferromagnetic behavior to a disordered one; in the high
temperature region a maximum (which has been related to a "gradual"
metal--insulator transition) is found in the specific heat for very large
values of the Coulomb repulsion.
| 1992-11-18
| 2009-10-22
|
[
"cond-mat"
] |
Alessandro Pelizzola
|
cond-mat/9211009
|
The fermion sign problem: A new decoupling transformation, and a new
simulation algorithm
|
We discuss the Fermion sign problem and, by examining a very general
Hubbard-Stratonovich (HS) transformation, argue that the sign problem cannot be
solved with such methods. We propose a different kind of transformation which,
while not solving the sign problem, shows more detailed information about the
system. With our transformation it is {\it trivial} to tell which auxiliary
field configurations give a positive sign and which give a negative sign. We
then discuss briefly various properties of this transformation and construct a
new algorithm which with one simulation gives results for a whole range of
particle densities and Hubbard $U$ values, positive and negative. Our approach
is in excellent agreement with exact calculations.
| 1992-11-17
| 2011-08-11
|
[
"cond-mat",
"hep-lat"
] |
Ghassan George Batrouni and Philippe de Forcrand
|
cond-mat/9211007
|
Singularity spectrum of self-organized criticality
|
I introduce a simple continuous probability theory based on the
Ginzburg-Landau equation that provides for the first time a common analytical
basis to relate and describe the main features of two seemingly different
phenomena of condensed-matter physics, namely self-organized criticality and
multifractality. Numerical support is given by a comparison with reported
simulation data. Within the theory the origin of self-organized critical
phenomena is analysed in terms of a nonlinear singularity spectrum different
from the typical convex shape due to multifractal measures.
| 1992-11-16
| 2008-12-24
|
[
"cond-mat"
] |
E. Canessa (ICTP-Trieste, Italy)
|
cond-mat/9211006
|
Cluster Algorithm for Vertex Models
|
We present a new type of cluster algorithm that strongly reduces critical
slowing down in simulations of vertex models. Since the clusters are closed
paths of bonds, we call it the {\em loop algorithm}. The basic steps in
constructing a cluster are the break-up and the freezing of vertices. We
concentrate on the case of the F model, which is a subset of the 6-vertex model
exhibiting a Kosterlitz-Thouless transition. The loop algorithm is also
applicable to simulations of other vertex models and of one and two-dimensional
quantum spin systems.
| 1992-11-16
| 2009-01-23
|
[
"cond-mat",
"hep-lat"
] |
H.G. Evertz, G. Lana and M. Marcu
|
cond-mat/9211008
|
Rigid Chiral Membranes
|
Statistical ensembles of flexible two-dimensional fluid membranes arise
naturally in the description of many physical systems. Typically one encounters
such systems in a regime of low tension but high stiffness against bending,
which is just the opposite of the regime described by the Polyakov string. We
study a class of couplings between membrane shape and in-plane order which
break 3-space parity invariance. Remarkably there is only {\it one} such
allowed coupling (up to boundary terms); this term will be present for any
lipid bilayer composed of tilted chiral molecules. We calculate the
renormalization-group behavior of this relevant coupling in a simplified model
and show how thermal fluctuations effectively reduce it in the infrared.
| 1992-11-16
| 2016-08-31
|
[
"cond-mat",
"hep-th"
] |
Philip Nelson and Thomas Powers
|
cond-mat/9211005
|
Spin-Wave Theory of the Spiral Phase of the t-J Model
|
A graded H.P,realization of the SU(2|1) algebra is proposed.A spin-wave
theory with a condition that the sublattice magnetization is zero is
discussed.The long-range spiral phase is investigated.The spin-spin correlator
is calculated.
| 1992-11-10
| 2009-10-22
|
[
"cond-mat"
] |
N.I.Karchev and T.S.Hristov
|
cond-mat/9211003
|
Infinite-Scale Percolation in a New Type of Branching Diffusion
Processes
|
We give an account of matter and (basically) a solution of a new class of
problems synthesizing percolation theory and branching diffusion processes.
They led us to realizing a novel type of stochastic processes, namely branching
processes with diffusion on the space of parameters distinguishing the
branching `particles' each other.
| 1992-11-04
| 2011-12-08
|
[
"cond-mat",
"hep-lat"
] |
A.Mezhlumian and S.A.Molchanov
|
cond-mat/9211004
|
Level repulsion in integrable and almost-integrable quantum spin models
|
The repartition of the separation between energy levels of various isotropic
S=1/2 antiferromagnetic chains is studied numerically with the aim of
investigating the transition from integrable to non-integrable systems. We
begin by displaying the level separation distribution of the integrable Bethe
chain. Then two non-integrable systems, two coupled chains and a
next-nearest-neighbor coupled chain, are studied as a function of the coupling.
We examine how the level spacing evolves from the Poisson distribution to the
GOE distribution. Finally we consider the Haldane-Shastry $1/r^{2}$ model. A
number of conclusions regarding the behaviour and relevance of the level
spacing distribution in these spin systems is drawn.
| 1992-11-04
| 2009-10-22
|
[
"cond-mat"
] |
Theodore C. Hsu and J.C. Angles d'Auriac
|
cond-mat/9211001
|
Exact Solution of an Electronic Model of Superconductivity in 1+1
Dimensions
|
We study a superconducting integrable model of strongly correlated electrons
in 1+1 dimensions. We construct all six Bethe Ans\"atze for the model and give
explicit expressions for lowest conservation laws. We also prove a lowest
weight theorem for the Bethe-Ansatz states.
| 1992-11-03
| 2015-06-25
|
[
"cond-mat"
] |
Fabian H.L. Essler, Vladimir E. Korepin, Kareljan Schoutens
|
cond-mat/9211002
|
Spin tunneling in the Kagom\'e antiferromagnet
|
The collective tunneling of a small cluster of spins between two degenerate
ground state configurations of the Kagom\'{e}-lattice quantum Heisenberg
antiferromagnet is \mbox{studied}. The cluster consists of the six spins on a
hexagon of the lattice. The resulting tunnel splitting energy $\Delta$ is
calculated in detail, including the prefactor to the exponential $\exp(- \SSo /
\hbar)$. This is done by setting up a coherent spin state path integral in
imaginary time and evaluating it by the method of steepest descent. The hexagon
tunneling problem is mapped onto a much simpler tunneling problem, involving
only one collective degree of freedom, which can be treated by known methods.
It is found that for half-odd-integer spins, the tunneling amplitude and the
tunnel splitting energy are exactly zero, because of destructive interference
between symmetry-related $(+)$-instanton and $(-)$-instanton tunneling paths.
This destructive interference is shown to occur also for certain larger loops
of spins on the Kagom\'{e} lattice. For small, integer spins, our results
suggest that tunneling strongly competes with \mbox{in-plane}
order-from-disorder selection effects; it constitutes a disordering mechanism
that might drive the system into a partially disordered ground state, related
to a spin nematic.
| 1992-11-03
| 2009-10-22
|
[
"cond-mat"
] |
Jan von Delft and Christopher L. Henley (Laboratory of Atomic and
Solid State Physics, Cornell University, Ithaca, NY)
|
cond-mat/9210028
|
The Third Virial Coefficient of Free Anyons
|
We use a path integral representation for the partition function of
non-interacting anyons confined in a harmonic oscillator potential in order to
prove that the third virial coefficient of free anyons is finite, and to
calculate it numerically. Our results together with previously known results
are consistent with a rapidly converging Fourier series in the statistics
angle.
| 1992-10-30
| 2009-10-22
|
[
"cond-mat",
"hep-th"
] |
Jan Myrheim and K{\aa}re Olaussen
|
cond-mat/9210027
|
Absence of Definite Scaling Laws in Raman Scattering from Fractals
|
The frequency dependence of the Raman coupling coefficient $C(\omega)$ is
calculated numerically for square and cubic percolation clusters. No general
scaling law in terms of the macroscopic parameters such as the fractal
dimension $D$ or the spectral dimension $\overline d$ is found. $C(\omega)$ is
sensitive to the microscopic structure of the clusters and depends on: site- or
bond-percolation, presence or absence of dangling bonds, scattering mechanism
and polarization, presence or absence of polarizability disorder. This
situation makes the derivation of macroscopic parameters from Raman experiments
unreliable.
| 1992-10-30
| 2007-05-23
|
[
"cond-mat"
] |
P.Benassi, O.Pilla, G.Viliani, G.Ruocco, G.Signorelli, V.Mazzacurati
and M.Montagna
|
cond-mat/9210026
|
Narrow band noise as a model of time-dependent accelerations: study of
the stability of a fluid surface in a microgravity environment
|
We introduce a stochastic model to analyze in quantitative detail the effect
of the high frequency components of the residual accelerations onboard
spacecraft (often called g-jitter) on fluid motion. The residual acceleration
field is modeled as a narrow band noise characterized by three independent
parameters: its intensity $G^{2}$, a dominant frequency $\Omega$, and a
characteristic spectral width $\tau^{-1}$. The white noise limit corresponds to
$\Omega \tau \rightarrow 0$, with $G^{2} \tau$ finite, and the limit of a
periodic g-jitter (or deterministic limit) can be recovered for $\Omega \tau
\rightarrow \infty$, $G^{2}$ finite. The analysis of the response of a fluid
surface subjected to a fluctuating gravitational field leads to the stochastic
Mathieu equation driven by both additive and multiplicative noise. We discuss
the stability of the solutions of this equation in the two limits of white
noise and deterministic forcing, and in the general case of narrow band noise.
The results are then applied to typical microgravity conditions.
| 1992-10-28
| 2007-05-23
|
[
"cond-mat"
] |
Jaume Casademunt, Wenbin Zhang, Jorge Vinals, R.F. Sekerka
|
cond-mat/9210025
|
Collective Effects in Random Sequential Adsorption of Diffusing Hard
Squares
|
We study by Monte Carlo computer simulations random sequential adsorption
(RSA) with diffusional relaxation, of lattice hard squares in two dimensions.
While for RSA without diffusion the coverage approaches its maximum jamming
value (large-time fractional coverage) exponentially, added diffusion allows
the deposition process to proceed to the full coverage. The approach to the
full coverage is consistent with the t**(-1/2) power law reminiscent of the
equilibrium cluster coarsening in models with nonconserved order-parameter
dynamics.
| 1992-10-24
| 2014-10-13
|
[
"cond-mat",
"hep-lat"
] |
J.-S. Wang, P. Nielaba, V. Privman
|
cond-mat/9210021
|
Static Response Function for Longitudinal and Transverse Excitations in
Superfluid Helium
|
The sum rule formalism is used to evaluate rigorous bounds for the density
and current static response functions in superfluid helium at zero temperature.
Both lower and upper bounds are considered. The bounds are expressed in terms
of ground state properties (density and current correlation funtions) and of
the interatomic potential. The results for the density static response
significantly improve the Feynman approximation and turn out to be close to the
experimental (neutron scattering) data. A quantitative prediction for the
transverse current response is given. The role of one-phonon and multi-particle
excitations in the longitudinal and transverse channels is discussed.
(Phys.Rev.B, in press)
| 1992-10-23
| 2009-10-22
|
[
"cond-mat"
] |
F.Dalfovo and S.Stringari
|
cond-mat/9210024
|
The Supercooling of a Nematic Liquid Crystal
|
We investigate the supercooling of a nematic liquid crystal using fluctuating
non-linear hydrodynamic equations. The Martin-Siggia-Rose formalism is used to
calculate renormalized transport coefficients to one-loop order. Similar
theories for isotropic liquids have shown substantial increases of the
viscosities as the liquid is supercooled or compressed due to feedback from the
density fluctuations which are freezing. We find similar results here for the
longitudinal and various shear viscosities of the nematic. However, the two
viscosities associated with the nematic director motion do not grow in any
dramatic way; i.e.\ there is no apparent freezing of the director modes within
this hydrodynamic formalism. Instead a glassy state of the nematic may arise
from a ``random anisotropy" coupling of the director to the frozen density.
| 1992-10-23
| 2009-10-22
|
[
"cond-mat"
] |
P.De, Robert Pelcovits, E. Vogel, J. Vogel
|
cond-mat/9210023
|
Uncertainty Principle and Off-Diagonal Long Range Order in the
Fractional Quantum Hall Effect
|
A natural generalization of the Heisenberg uncertainty principle inequality
holding for non hermitian operators is presented and applied to the fractional
quantum Hall effect (FQHE). This inequality was used in a previous paper to
prove the absence of long range order in the ground state of several 1D systems
with continuous group symmetries. In this letter we use it to rule out the
occurrence of Bose-Einstein condensation in the bosonic representation of the
FQHE wave function proposed by Girvin and MacDonald. We show that the absence
of off-diagonal long range order in this 2D problem is directly connected with
the $q^2$ behavior of the static structure function $S(q)$ at small momenta.
| 1992-10-23
| 2009-10-22
|
[
"cond-mat"
] |
L.Pitaevskii and S.Stringari
|
cond-mat/9210022
|
Correlaction Effects on the Band Gap of Conducting Polymers
|
By applying the projection technique to the computation of excitation
energies, we study the correlation effects on the band gap of conducting
polymers. In the presence of an additional electron or hole, the correlation
induces a polarization cloud around the addi- tional particle, which forms a
polaron. For the excitation energy of a polaron,there is a competition between
a {\it loss} of the correla- tion energy in the ground state and a {\it gain}
of polarization energy. For the Hubbard interaction, the {\it loss} of
correlation energy is dominant and correlations increase the band
gap.However,for long-range interactions, the {\it gain} of polarization energy
is dominant and correlations decrease the band gap. Screening the long- range
interaction suppresses the {\it gain}of the polarization energy so that
correlations again increase the band gap.A small dimerization is always
favorable to the correlation effects. For {\it trans}-poly- acetylene, we
obtain the on-site repulsion $U=4.4$eV and the nearest- neighbor interaction
$V=0.8$ eV. The screening of $\pi$ electrons due to the polarizability of
$\sigma$ electrons is quite strong. ** to be published in Phys. Rev. B
| 1992-10-23
| 2009-10-22
|
[
"cond-mat"
] |
C.Q.Wu (Max-Planck-Institue f\"ur Festk\"orperforschung, Stuttgart,
Germany)
|
cond-mat/9210020
|
Magnetic field effects on non-periodic superlattice structures
|
A simple numerical method to study the effect of an applied magnetic field on
the energy spectrum of non-periodic superlattice structures is presented. The
magnetic field could be either parallel or perpendicular to the growth
direction. Our method is based on the transfer matrix technique and on the
effective mass approximation. We discuss the advantages and disadvantages of
the proposed approach using several examples. In particular, we study the
perturbation to the energy spectrum of periodic superlattice induced by the
introduction of an enlarged well. We found that these perturbations are
negligible for B//z but relevant for B$\perp $z. Preliminary results for
Fibonacci superlattices in magnetic fields are presented as well. In these
quasi-periodic structures the energy levels become strongly dispersive in
presence of a perpendicular magnetic field.
| 1992-10-22
| 2009-10-22
|
[
"cond-mat"
] |
H. Cruz, F. Piazza, and L. Pavesi
|
cond-mat/9210019
|
Response functions and Spectrum of Collective Excitations of Fractional
Quantum Hall Effect Systems
|
We calculate the electromagnetic response functions of a Fractional Quantum
Hall system within the framework of the fermion Chern-Simons theory for the
Fractional Hall Effect (FQHE) which we developed before. Our results are valid
in a semiclassical expansion around the average field approximation (AFA). We
reexamine the AFA and the role of fluctuations. We argue that,
order-\-by-\-order in the semiclassical expansion, the response functions obey
the correct symmetry properties required by Galilean and Gauge Invariance and
by the incompressibility of the fluid. In particular, we find that the
low-momentum limit of the semiclassical approximation to the response functions
is exact and that it saturates the $f$-sum rule.We obtain the spectrum of
collective excitations of FQHE systems in the low-momentum limit. We find a
rich spectrum of modes which includes a host of quasiparticle- quasihole bound
states and, in general,two collective modes coalescing at the cyclotron
frequency. The Hall conductance is obtained from the current-density
correlation function, and it has the correct value already at the semiclassical
level. We applied these results to the problem of the screening of external
charges and fluxes by the electron fluid, and obtained asymptotic expressions
of the charge and current density profiles, for different types of
interactions. Finally, we reconsider the anyon superfluid within our scheme and
derive the spectrum of collective modes for interacting hard-core bosons and
semions. In addition to the gapless phase mode, we find a set of gapped
collective modes.
| 1992-10-21
| 2009-10-22
|
[
"cond-mat"
] |
Ana Lopez and Eduardo Fradkin
|
cond-mat/9210018
|
Hysteresis and hierarchies: dynamics of disorder-driven first-order
phase transformations
|
We use the zero-temperature random-field Ising model to study hysteretic
behavior at first-order phase transitions. Sweeping the external field through
zero, the model exhibits hysteresis, the return-point memory effect, and
avalanche fluctuations. There is a critical value of disorder at which a jump
in the magnetization (corresponding to an infinite avalanche) first occurs. We
study the universal behavior at this critical point using mean-field theory,
and also present preliminary results of numerical simulations in three
dimensions.
| 1992-10-20
| 2009-01-23
|
[
"cond-mat"
] |
James P. Sethna, Karin Dahmen, Sivan Kartha, James A. Krumhansl, Bruce
W. Roberts, and Joel D. Shore
|
cond-mat/9210017
|
Biharmonic pattern selection
|
A new model to describe fractal growth is discussed which includes effects
due to long-range coupling between displacements $u$. The model is based on the
biharmonic equation $\nabla^{4}u =0$ in two-dimensional isotropic defect-free
media as follows from the Kuramoto-Sivashinsky equation for pattern formation
-or, alternatively, from the theory of elasticity. As a difference with
Laplacian and Poisson growth models, in the new model the Laplacian of $u$ is
neither zero nor proportional to $u$. Its discretization allows to reproduce a
transition from dense to multibranched growth at a point in which the growth
velocity exhibits a minimum similarly to what occurs within Poisson growth in
planar geometry. Furthermore, in circular geometry the transition point is
estimated for the simplest case from the relation $r_{\ell}\approx L/e^{1/2}$
such that the trajectories become stable at the growing surfaces in a
continuous limit. Hence, within the biharmonic growth model, this transition
depends only on the system size $L$ and occurs approximately at a distance $60
\%$ far from a central seed particle. The influence of biharmonic patterns on
the growth probability for each lattice site is also analysed.
| 1992-10-20
| 2009-10-22
|
[
"cond-mat"
] |
Wei Wang and E. Canessa (Condensed Matter Group, ICTP, Trieste, Italy)
|
cond-mat/9210016
|
Spin-Charge separation in a model of two coupled chains
|
A model of interacting electrons living on two chains coupled by a transverse
hopping $t_\perp$, is solved exactly by bosonization technique. It is shown
that $t_\perp$ does modify the shape of the Fermi surface also in presence of
interaction, although charge and spin excitations keep different velocities
$u_\rho$, $u_\sigma$. Two different regimes occur: at short distances, $x\ll
\xi = (u_\rho - u_\sigma)/4t_\perp$, the two chain model is not sensitive to
$t_\perp$, while for larger separation $x\gg \xi$ inter--chain hopping is
relevant and generates further singularities in the electron Green function
besides those due to spin-charge decoupling. (2 figures not included. Figure
requests: FABRIZIO@ITSSISSA)
| 1992-10-19
| 2009-10-22
|
[
"cond-mat"
] |
M. Fabrizio and A. Parola
|
cond-mat/9210015
|
Many Body Theory of Charge Transfer in Hyperthermal Atomic Scattering
|
We use the Newns-Anderson Hamiltonian to describe many-body electronic
processes that occur when hyperthermal alkali atoms scatter off metallic
surfaces. Following Brako and Newns, we expand the electronic many-body
wavefunction in the number of particle-hole pairs (we keep terms up to and
including a single particle-hole pair). We extend their earlier work by
including level crossings, excited neutrals and negative ions. The full set of
equations of motion are integrated numerically, without further approximations,
to obtain the many-body amplitudes as a function of time. The velocity and
work-function dependence of final state quantities such as the distribution of
ion charges and excited atomic occupancies are compared with experiment. In
particular, experiments that scatter alkali ions off clean Cu(001) surfaces in
the energy range 5 to 1600 eV constrain the theory quantitatively. The
neutralization probability of Na$^+$ ions shows a minimum at intermediate
velocity in agreement with the theory. This behavior contrasts with that of
K$^+$, which shows ... (7 figures, not included. Figure requests:
jbm@yollabolly.physics.brown.edu)
| 1992-10-17
| 2009-10-22
|
[
"cond-mat"
] |
J. B. Marston, D. R. Andersson, E. R. Behringer, B. H. Cooper, C. A.
DiRubio, G. A. Kimmel, and C. Richardson
|
cond-mat/9210012
|
Ordering and finite-size effects in the dynamics of one-dimensional
transient patterns
|
We introduce and analyze a general one-dimensional model for the description
of transient patterns which occur in the evolution between two spatially
homogeneous states. This phenomenon occurs, for example, during the
Freedericksz transition in nematic liquid crystals.The dynamics leads to the
emergence of finite domains which are locally periodic and independent of each
other. This picture is substantiated by a finite-size scaling law for the
structure factor. The mechanism of evolution towards the final homogeneous
state is by local roll destruction and associated reduction of local
wavenumber. The scaling law breaks down for systems of size comparable to the
size of the locally periodic domains. For systems of this size or smaller, an
apparent nonlinear selection of a global wavelength holds, giving rise to long
lived periodic configurations which do not occur for large systems. We also
make explicit the unsuitability of a description of transient pattern dynamics
in terms of a few Fourier mode amplitudes, even for small systems with a few
linearly unstable modes.
| 1992-10-16
| 2009-10-22
|
[
"cond-mat"
] |
A. Amengual, E. Hernandez-Garcia, and M. San Miguel
|
cond-mat/9210013
|
Numerical studies of tunneling in a nonharmonic time-dependent potential
|
Azbel' has recently carried out a WKB-analysis of the effects of a
nonharmonic time-dependent perturbation embedded in an opaque potential
barrier. He suggests the existence of three different transmission regimes:
direct tunneling, activation assisted tunneling, and elevator resonant
activation. We address the same problem with a numerical technique, and find
qualitative agreement with Azbel's picture.
| 1992-10-16
| 2009-10-22
|
[
"cond-mat"
] |
J. A. St{\o}vneng and A.-P. Jauho
|
cond-mat/9210014
|
On the Scale-Invariant Distribution of the Diffusion Coefficient for
Classical Particles Diffusing in Disordered Media.-
|
The scaling form of the whole distribution P(D) of the random diffusion
coefficient D(x) in a model of classically diffusing particles is investigated.
The renormalization group approach above the lower critical dimension d=0 is
applied to the distribution P(D) using the n-replica approach. In the annealed
approximation (n=1), the inverse gaussian distribution is found to be the
stable one under rescaling. This identification is made based on symmetry
arguments and subtle relations between this model and that of fluc- tuating
interfaces studied by Wallace and Zia. The renormalization-group flow for the
ratios between consecutive cumulants shows a regime of pure diffusion for small
disorder, in which P(D) goes to delta(D-<D>), and a regime of strong disorder
where the cumulants grow infinitely large and the diffusion process is ill
defined. The boundary between these two regimes is associated with an unstable
fixed-point and a subdiffusive behavior: <x**2>=Ct**(1-d/2). For the quenched
case (n goes to 0) we find that unphysical operators are generated raisng
doubts on the renormalizability of this model. Implications to other random
systems near their lower critical dimension are discussed.
| 1992-10-16
| 2009-10-22
|
[
"cond-mat",
"hep-th"
] |
Yan-Chr Tsai and Yonathan Shapir
|
cond-mat/9210011
|
Generalized spin density wave state of the Hubbard model on the C12 and
C60 clusters
|
The one-band Hubbard model at half-filling on a truncated tetrahedron
(C$_{12}$), and on the C$_{60}$ molecule is studied. Within the Hartree-Fock
approximation, we find a magnetic-like instability of the `Fermi sea' towards a
spin-ordered phase for an intermediate value of the coupling ${\rm
(U/t)_c}\approx 2.6$. The ordered phase presents a spin arrangement similar to
that of the classical Heisenberg model defined on the same clusters. We study
the linear excitations around the Hartree-Fock ground states using the
random-phase approximation. On a finite cluster, we expect that these results
signal the presence of a $rapid$ $crossover$ between a paramagnetic region and
a regime where spin correlations are important. The relationship with the
Heisenberg limit (large ${\rm U/t}$) is discussed. Finally, we comment on
implications of our results for purely repulsive models of superconductivity in
alkali-metal-doped fullerenes.
| 1992-10-14
| 2014-10-13
|
[
"cond-mat"
] |
L. Bergomi, J. P. Blaizot, Th. Jolicoeur and E. Dagotto
|
cond-mat/9210008
|
String Defects in Condensed Matter Systems as Optical Fibers
|
We analyze the core structure of string defects in various condensed matter
systems, such as nematic liquid crystals and superfluid helium, and argue that
in certain cases the variation of the refractive index near the core is such
that it can lead to total internal reflection of light travelling along the
string core. These strings thus behave as optical fibers providing a
qualitatively new approach to optical fibers. We present a candidate for such a
fiber by looking at string segments in a thin nematic liquid crystal film on
water. We discuss various possibilities for constructing such fibers as well as
possible technological applications.
| 1992-10-14
| 2007-05-23
|
[
"cond-mat",
"hep-ph"
] |
Ajit Mohan Srivastava
|
cond-mat/9210010
|
Dimerization structures on the metallic and semiconducting fullerene
tubules with half-filled electrons
|
Possible dimerization patterns and electronic structures in fullerene tubules
as the one-dimensional pi-conjugated systems are studied with the extended
Su-Schrieffer-Heeger model. We assume various lattice geometries, including
helical and nonhelical tubules. The model is solved for the half-filling case
of $\pi$-electrons. (1) When the undimerized systems do not have a gap, the
Kekule structures prone to occur. The energy gap is of the order of the room
temperatures at most and metallic properties would be expected. (2) If the
undimerized systems have a large gap (about 1eV), the most stable structures
are the chain-like distortions where the direction of the arranged
trans-polyacetylene chains is along almost the tubular axis. The electronic
structures are ofsemiconductors due to the large gap.
| 1992-10-14
| 2007-05-23
|
[
"cond-mat"
] |
Kikuo Harigaya (Fundamental Physics Section, Physical Science
Division, Electrotechnical Laboratory, Japan), Mitsutaka Fujita (Institute of
Materials Science, University of Tsukuba, Japan)
|
cond-mat/9210009
|
Phase Ordering Dynamics in the Continuum q-state Clock Model
|
The order parameter correlation function of the nonconserved, continuum
$q$-state clock model is evaluated in the asymptotic scaling limit, during the
phase ordering process after a temperature quench. The short distance behavior
of the order parameter scaling function exhibits explicit crossover from that
characteristic of the Ising universality class to that of the $O(2)$ model.
| 1992-10-14
| 2009-10-22
|
[
"cond-mat"
] |
Fong Liu and Gene F. Mazenko
|
cond-mat/9210007
|
Bosonization and Fermion Liquids in Dimensions Greater Than One
|
(Revised, with postscript figures appended, corrections and added comments.)
We develop and describe new approaches to the problem of interacting Fermions
in spatial dimensions greater than one. These approaches are based on
generalizations of powerful tools previously applied to problems in one spatial
dimension. We begin with a review of one-dimensional interacting Fermions. We
then introduce a simplified model in two spatial dimensions to study the role
that spin and perfect nesting play in destabilizing Fermion liquids. The
complicated functional renormalization group equations of the full problem are
made tractable in our model by replacing the continuum of points that make up
the closed Fermi line with four Fermi points. Despite this drastic
approximation, the model exhibits physically reasonable behavior both at
half-filling (where instabilities occur) and away from half-filling (where a
Luttinger liquid arises). Next we implement the Bosonization of higher
dimensional Fermi surfaces introduced by Luther and advocated most recently by
Haldane. Bosonization incorporates the phase space and small-angle scattering
.... (7 figures, appended as a postscript file at the end of the TeX file).
| 1992-10-10
| 2009-10-22
|
[
"cond-mat",
"hep-th"
] |
A. Houghton and J. B. Marston
|
cond-mat/9210006
|
Once again about interchain hopping
|
Renormalization group equations and a phase diagram are derived for a system
of two chains with a single-electron hopping between chains in order to correct
the results of a recent paper by F.~V.~Kusmartsev, A.~Luther, and A.~Nersesyan,
Pis'ma v Zh.\ Exp.\ Teor.\ Fiz.\ {\bf 55}, 692 (1992) [JETP Lett.\ {\bf 55},
724 (1992)].
| 1992-10-09
| 2008-02-03
|
[
"cond-mat"
] |
Victor M. Yakovenko
|
cond-mat/9210005
|
Multicanonical Study of the 3D Ising Spin Glass
|
We simulated the Edwards-Anderson Ising spin glass model in three dimensions
via the recently proposed multicanonical ensemble. Physical quantities such as
energy density, specific heat and entropy are evaluated at all temperatures. We
studied their finite size scaling, as well as the zero temperature limit to
explore the ground state properties.
| 1992-10-07
| 2009-10-22
|
[
"cond-mat",
"hep-lat"
] |
B.A.Berg, T.Celik and U.Hansmann
|
cond-mat/9210004
|
A new Proposal for a Quasielectron Trial Wavefunction for the FQHE on a
Disk
|
In this letter, we propose a new quasielectron trial wavefunction for $N$
interacting electrons in two dimensions moving in a strong magnetic field in a
disk geometry. Requiring that the trial wavefunction exhibits the correct
filling factor of a quasielectron wavefunction, we obtain $N+1$ angular
momentum eigenfunctions. The expectation values of the energy are calculated
and compared with the data of an exact numerical diagonalization.
| 1992-10-06
| 2010-12-17
|
[
"cond-mat",
"hep-th"
] |
Marcus Kasner and Walter Apel (Physikalisch-Technische Bundesanstalt
Braunschweig, PF 3345, D-W-3300 Braunschweig, Germany)
|
cond-mat/9210003
|
Pressure Induced Topological Phase Transitions in Membranes
|
Some highly unusual features of a lipid-water liquid crystal are revealed by
high pressure x-ray diffraction, light scattering and dilatometric studies of
the lamellar (bilayer $L_{\alpha}$) to nonlamellar inverse hexagonal ($H_{II}$)
phase transition. (i) The size of the unit cell of the $H_{II}$ phase increases
with increasing pressure. (ii) The transition volume, $\Delta V_{bh}$,
decreases and appears to vanish as the pressure is increased. (iii) The
intensity of scattered light increases as $\Delta V_{bh}$ decreases. Data are
presented which suggest that this increase is due to the formation of an
intermediate cubic phase, as predicted by recent theoretical suggestions of the
underlying universal phase sequence.
| 1992-10-04
| 2009-10-22
|
[
"cond-mat"
] |
P.T.C. So, Sol M. Gruner and Shyamsunder Erramilli
|
cond-mat/9210002
|
Exact Solution of a Phase Separation Model with Conserved Order
Parameter Dynamics
|
Pairwise particle-exchange model on a linear lattice is solved exactly by a
new rate-equation method. Lattice sites are occupied by particles A and B which
can exchange irreversibly provided the local energy in reduced. Thus, the model
corresponds to a zero-temperature Kawasaki-type phase separation process. Due
to local order-parameter conservation, the dynamics reaches a frozen state at
large times, the structure of which depends on the initial conditions.
| 1992-10-02
| 2014-10-13
|
[
"cond-mat",
"hep-lat"
] |
Vladimir Privman
|
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