title: Diffusion of gold nanoclusters on graphite

abstract:
  We present a detailed molecular-dynamics study of the diffusion and
coalescence of large (249-atom) gold clusters on graphite surfaces. The
diffusivity of monoclusters is found to be comparable to that for single
adatoms. Likewise, and even more important, cluster dimers are also found to
diffuse at a rate which is comparable to that for adatoms and monoclusters. As
a consequence, large islands formed by cluster aggregation are also expected to
be mobile. Using kinetic Monte Carlo simulations, and assuming a proper scaling
law for the dependence on size of the diffusivity of large clusters, we find
that islands consisting of as many as 100 monoclusters should exhibit
significant mobility. This result has profound implications for the morphology
of cluster-assembled materials.


title:
Comment on the paper `Inelastic granular gas: Computer simulations and
  kinetic theory of the cooling state' by J.M. Salazar and L. Brenig

abstract:
  A hierarchy of equations was introduced recently to describe the kinetics of
homogeneous cooling of the gas of inelastic hard spheres. It is argued that
this hierarchy does not describe this system accurately, and a simple test for
this is proposed. A stochastic interpretation of the hierarchy is presented.


title: Dynamical phases and hysteresis in a simple one-lane traffic model

abstract:
  A two parameter model for single lane car-following is introduced and its
equilibrium and non-equilibrium properties are studied. Despite its simplicity,
this model exhibits a rich phenomenology, analogous to that observed in real
traffic, like transitions between different dynamical regimes and hysteresis in
the fundamental flux-density diagram. We show that traffic jams can
spontaneously appear in clustered-like structures. In the jammed phase, we
observe a slow relaxation phenomenon ruled by the outgoing car flux that
determines the hysteretic dependence of the fundamental flux-density diagram.
Coexisting phase regimes are also evidenced so as propagating or stationary
density waves. The model can be easily calibrated to reproduce experimental
observations.


title:
A Gapless Theory of Bose-Einstein Condensation in Dilute Gases at Finite
  Temperature

abstract:
  In this paper we develop a gapless theory of BEC which can be applied to both
trapped and homogeneous gases at zero and finite temperature. The many-body
Hamiltonian for the system is written in a form which is approximately
quadratic with higher order cubic and quartic terms. The quadratic part is
diagonalized exactly by transforming to a quasiparticle basis, while the
non-quadratic terms are dealt with using first and second order perturbation
theory. The conventional treatment of these terms, based on factorization
approximations, is shown to be inconsistent.
  Infra-red divergences can appear in individual terms of the perturbation
expansion, but we show analytically that the total contribution beyond
quadratic order is finite. The resulting excitation spectrum is gapless and the
energy shifts are small for a dilute gas away from the critical region,
justifying the use of perturbation theory. Ultra-violet divergences can appear
if a contact potential is used to describe particle interactions. We show that
the use of this potential as an approximation to the two-body T-matrix leads
naturally to a high-energy renormalization.
  The theory developed in this paper is therefore well-defined at both low and
high energy and provides a systematic description of Bose-Einstein condensation
in dilute gases. It can therefore be used to calculate the energies and decay
rates of the excitations of the system at temperatures approaching the phase
transition.


title: Far-infrared magnetotransmission of YBa2(ZnxCu(1-x))3O(7-d)

abstract:
  Measurements of the far infrared magnetotransmission of
YBa2(ZnxCu(1-x))3O(7-d) thin film (x = 0.025) deposited on a wedged MgO
substrate are reported. The application of magnetic field perpendicular to the
ab plane produces at low temperature a linear increase of transmission for
frequencies below 30 cm-1. We present a model of high frequency vortex dynamics
which qualitatively explains these results.


title: How to break the replica symmetry in structural glasses

abstract:
  The variational principle (VP) has been used to capture the metastable states
of a glass-forming molecular system without quenched disorder. It has been
shown that VP naturally leads to a self-consistent random field Ginzburg-Landau
model (RFGLM). In the framework of one-step replica symmetry breaking (1-RSB)
the general solution of RFGLM is discussed in the vicinity of the spinodal
temperature T_{A} in terms of ``hidden'' formfactors $\tilde g(k)$, g_{0}(k)
and $\Delta(k)$. The self-generated disorder spontaneously arises. It is argued
that at T < T_{A} the activated dynamics is dominant.


title: Optical conductivity of the half-filled Hubbard chain

abstract:
  We combine well-controlled analytical and numerical methods to determine the
optical conductivity of the one-dimensional Mott-Hubbard insulator at zero
temperature. A dynamical density-matrix renormalization group method provides
the entire absorption spectrum for all but very small coupling strengths. In
this limit we calculate the conductivity analytically using exact
field-theoretical methods. Above the Lieb-Wu gap the conductivity exhibits a
characteristic square-root increase. For small to moderate interactions, a
sharp maximum occurs just above the gap. For larger interactions, another weak
feature becomes visible around the middle of the absorption band.


title: Time-dependent transport in interacting mesoscopic systems

abstract:
  We review recent applications of the nonequilibrium Green function technique
to time-dependent transport in mesoscopic systems.


title: Electric field in type II superconductors

abstract:
  Generally it is accepted that electric field E in type II superconductors is
created by the vortex motion, so that it is proportional to the vortex velocity
v_L. This assertion is based on the Josephson relation E = - v_L x B, which was
derived and is valid if no transport current is present. We present arguments
showing that if transport current is present, static electric field is
proportional to the relative velocity of vortices in respect to the velocity of
superconducting fluid v_s, so that in this case generalised Josephson relation
E = v_s - v_L x B is valid.


title: Statistics of Wave Functions in Coupled Chaotic Systems

abstract:
  Using the supersymmetry technique, we calculate the joint distribution of
local densities of electron wavefunctions in two coupled disordered or chaotic
quantum billiards. We find novel spatial correlations that are absent in a
single chaotic system. Our exact result can be interpreted for small coupling
in terms of the hybridization of eigenstates of the isolated billiards. We show
that the presented picture is universal, independent of microscopic details of
the coupling.


title: Spin analogs of proteins: scaling of "folding" properties

abstract:
  Reaching a ground state of a spin system is analogous to a protein evolving
into its native state. We study the ``folding'' times for various random Ising
spin systems and determine characteristic temperatures that relate to the
``folding''. Under optimal kinetic conditions, the ``folding'' times scale with
the system size as a power law with a non-universal exponent. This is similar
to what happens in model proteins. On the other hand, the scaling behavior of
the characteristic temperatures is different than in model proteins. Both in
the spin systems and in proteins, the folding properties deteriorate with the
system size.


title: Gapped Phases of Quantum Wires

abstract:
  We investigate possible nontrivial phases of a two-subband quantum wire. It
is found that inter- and intra-subband interactions may drive the electron
system of the wire into a gapped state. If the nominal electron densities in
the two subbands are sufficiently close to each other, then the leading
instability is the inter-subband charge-density wave (CDW). For large density
imbalance, the interaction in the inter-subband Cooper channel may lead to a
superconducting instability. The total charge-density mode, responsible for the
conductance of an ideal wire, always remains gapless, which enforces the
two-terminal conductance to be at the universal value of 2e^2/h per occupied
subband. On the contrary, the tunneling density of states (DOS) in the bulk of
the wire acquires a hard gap, above which the DOS has a non-universal
singularity. This singularity is weaker than the square-root divergency
characteristic for non-interacting quasiparticles near a gap edge due to the
"dressing" of massive modes by a gapless total charge density mode. The DOS for
tunneling into the end of a wire in a CDW-gapped state preserves the power-law
behavior due to the frustration the edge introduces into the CDW order. This
work is related to the vast literature on coupled 1D systems, and most of all,
on two-leg Hubbard ladders. Whenever possible, we give derivations of the
important results by other authors, adopted for the context of our study.


title:
Magnetization curves and ac susceptibilites in type-II superconductors:
  geometry-independent similarity and effect of irreversibility mechanisms

abstract:
  The magnetic characteristics for superconducting samples of different
geometries (plates and films of various widths) and orientation with respect to
external field are compared. A similarity is established between the
magnetization curves M(H) and the corresponding susceptibilities. A sign
reversal is predicted for the 3rd harmonic of the ac susceptibillity when the
irreversibility mechanism changes from bulk pinning to edge barrier. A mutual
influence of the edge barrier and bulk pinning on the magnetization curves and
field-dependent ac susceptibility is studied on the basis of an exactly
solvable model (narrow plate in a parallel field and/or narrow film in a
perpendicular magnetic field).


title:
Magnetic phenomena at and near nu =1/2 and 1/4: theory, experiment and
  interpretation

abstract:
  I show that the hamiltonian theory of Composite Fermions (CF) is capable of
yielding a unified description in fair agreement with recent experiments on
polarization P and relaxation rate 1/T_1 in quantum Hall states at filling nu =
p/(2ps+1), at and near nu = 1/2 and 1/4, at zero and nonzero temperatures. I
show how rotational invariance and two dimensionality can make the underlying
interacting theory behave like a free one in a limited context.


title: Dynamics of liquid 4He in Vycor

abstract:
  We have measured the dynamic structure factor of liquid 4He in Vycor using
neutron inelastic scattering. Well-defined phonon-roton (p-r) excitations are
observed in the superfluid phase for all wave vectors 0.3 < Q < 2.15. The p-r
energies and lifetimes at low temperature (T = 0.5 K) and their temperature
dependence are the same as in bulk liquid 4He. However, the weight of the
single p-r component does not scale with the superfluid fraction (SF) as it
does in the bulk. In particular, we observe a p-r excitation between T_c =
1.952 K, where SF = 0, and T_(lambda)=2.172 K of the bulk. This suggests, if
the p-r excitation intensity scales with the Bose condensate, that there is a
separation of the Bose-Einstein condensation temperature and the superfluid
transition temperature T_c of 4He in Vycor. We also observe a two-dimensional
layer mode near the roton wave vector. Its dispersion is consistent with
specific heat and SF measurements and with layer modes observed on graphite
surfaces.


title: Effect of the W-term for a t-U-W Hubbard ladder

abstract:
  Antiferromagnetic and d_{x2-y2}-pairing correlations appear delicately
balanced in the 2D Hubbard model. Whether doping can tip the balance to pairing
is unclear and models with additional interaction terms have been studied. In
one of these, the square of a local hopping kinetic energy H_W was found to
favor pairing. However, such a term can be separated into a number of simpler
processes and one would like to know which of these terms are responsible for
enhancing the pairing. Here we analyze these processes for a 2-leg Hubbard
ladder.


title: The Futility of Utility: how market dynamics marginalize Adam Smith

abstract:
  Econometrics is based on the nonempiric notion of utility. Prices, dynamics,
and market equilibria are supposed to be derived from utility. Utility is
usually treated by economists as a price potential, other times utility rates
are treated as Lagrangians. Assumptions of integrability of Lagrangians and
dynamics are implicitly and uncritically made. In particular, economists assume
that price is the gradient of utility in equilibrium, but I show that price as
the gradient of utility is an integrability condition for the Hamiltonian
dynamics of an optimization problem in econometric control theory. One
consequence is that, in a nonintegrable dynamical system, price cannot be
expressed as a function of demand or supply variables. Another consequence is
that utility maximization does not describe equiulibrium. I point out that the
maximization of Gibbs entropy would describe equilibrium, if equilibrium could
be achieved, but equilibrium does not describe real markets. To emphasize the
inconsistency of the economists' notion of 'equilibrium', I discuss both
deterministic and stochastic dynamics of excess demand and observe that Adam
Smith's stabilizing hand is not to be found either in deterministic or
stochastic dynamical models of markets, nor in the observed motions of asset
prices. Evidence for stability of prices of assets in free markets simply has
not been found.

categories: cond-mat.stat-mech chao-dyn nlin.CD q-fin.GN


title:
Role of f electrons in rare-earth and uranium intermetallics-An
  alternative look at heavy-fermion phenomena

abstract:
  The understanding of magnetic and electronic properties of rare-earth
intermetallics is summarized. The properties of NdNi5 or ErNi5 are understood
by considering a few electronic subsystems like the f electronic subsystem and
the conduction-electron subsystem. The localized f electrons can give a
substantial contribution to the low temperature specific heat with the entropy
of R ln2 in case of Kramers ions. In this view the heavy-fermion behaviour is
related with the removal of the Kramers degeneracy of the ground state of the f
electronic subsystem.


title:
Local structure of In_(0.5)Ga_(0.5)As from joint high-resolution and
  differential pair distribution function analysis

abstract:
  High resolution total and indium differential atomic pair distribution
functions (PDFs) for In_(0.5)Ga_(0.5)As alloys have been obtained by high
energy and anomalous x-ray diffraction experiments, respectively. The first
peak in the total PDF is resolved as a doublet due to the presence of two
distinct bond lengths, In-As and Ga-As. The In differential PDF, which involves
only atomic pairs containing In, yields chemical specific information and helps
ease the structure data interpretation. Both PDFs have been fit with structure
models and the way in that the underlying cubic zinc-blende lattice of
In_(0.5)Ga_(0.5)As semiconductor alloy distorts locally to accommodate the
distinct In-As and Ga-As bond lengths present has been quantified.


title: Time-resolved optical observation of spin-wave dynamics

abstract:
  We have created a nonequilibrium population of antiferromagnetic spin-waves
in Cr2O3, and characterized its dynamics, using frequency- and time-resolved
nonlinear optical spectroscopy of the exciton-magnon transition. We observe a
time-dependent pump-probe line shape, which results from excitation induced
renormalization of the spin-wave band structure. We present a model that
reproduces the basic characteristics of the data, in which we postulate the
optical nonlinearity to be dominated by interactions with long-wavelength
spin-waves, and the dynamics to be due to spin-wave thermalization.


title: Electronic Structure of Stripes in Two-Dimensional Hubbard Model

abstract:
  Focusing on La_{2-x}Sr_{x}CuO_{4}, we study the stripe structure by the
self-consistent mean-field theory of the Hubbard model. By introducing the
realistic Fermi surface topology, the SDW-gapped insulator is changed to
metallic. The solitonic features of the stripe structure and the contribution
of the mid-gap states are presented. We consider the band dispersion, the local
density of states, the spectral weight, and the optical conductivity,
associated with the solitonic structure. These results may provide important
information for the experimental research of the stripe structure, such as the
angle-resolved photoemission experiments. The ``Fermi surface'' shape is
changed depending on the ratio of the incommensurability delta and the hole
density n_h. In real space, only the stripe region is metallic when delta/n_h
is large.


title:
Dynamic charge density correlation function in weakly charged
  polyampholyte globules

abstract:
  We study solutions of statistically neutral polyampholyte chains containing a
large fraction of neutral monomers. It is known that, even if the quality of
the solvent with respect to the neutral monomers is good, a long chain will
collapse into a globule. For weakly charged chains, the interior of this
globule is semi-dilute. This paper considers mainly theta-solvents, and we
calculate the dynamic charge density correlation function g(k,t) in the
interior of the globules, using the quadratic approximation to the
Martin-Siggia-Rose generating functional. It is convenient to express the
results in terms of dimensionless space and time variables. Let R be the blob
size, and let T be the characteristic time scale at the blob level. Define the
dimensionless wave vector q = R k, and the dimensionless time s = t/T. We find
that for q<1, corresponding to length scales larger than the blob size, the
charge density fluctuations relax according to g(q,s) = q^2(1-s^(1/2)) at short
times s < 1, and according to g(q,s) = q^2 s^(-1/2) at intermediate times 1 < s
< q^(-4). We expect these results to be valid for wave vectors q > 0.1, where
entanglements are unimportant.


title: Quantum Chaos and Thermalization for Interacting Particles

abstract:
  In this review the problem of statistical description of isolated quantum
systems of interacting particles is discussed. Main attention is paid to a
recently developed approach which is based on chaotic properties of compound
states in the basis of non-interacting particles. In order to demonstrate the
most important aspects of this approach, the matrix model of two-body random
interaction between Fermi-particles has been used. Different problems have been
considered such as the onset of chaos and statistical equilibrium, the relation
between the structure of eigenstates and distribution of occupation numbers,
the emergence of the Fermi-Dirac distribution in isolated systems of finite
number of particles and many others. The application of the approach to
dynamical systems with the classical limit is discussed as well.


title: Spin-Peierls transition in NaV2O5 in high magnetic fields

abstract:
  We investigate the magnetic field dependence of the spin-Peierls transition
in NaV$_2$O$_5$ in the field range 16T-30T. The transition temperature exhibits
a very weak variation with the field, suggesting a novel mechanism for the
formation of the spin-Peierls state. We argue that a charge ordering transition
accompanied by singlet formation is consistent with our observations.


title: Distribution function of mesoscopic hopping conductance

abstract:
  We study by computer simulation distribution functions (DF) of mesoscopic
hopping conductance. The DFs obtained for one-dimensional systems were found to
be quite close to the predictions of the theory by Raikh and Ruzin. For D=2,
the DFs both for narrow system and thin film look similar (and close to the 1D
case).The distribution function for the conductance of the square sample is
nearly Gaussian.


title:
Long-range Casimir interactions between impurities in nematic liquid
  crystals and the collapse of polymer chains in such solvents

abstract:
  The elastic interactions between objects embedded in a nematic liquid crystal
are usually caused by the average distorsion-rather than by the fluctuations-of
the nematic orientational field. We argue that for sufficiently small
particles, the nematic-mediated interaction originates purely from the
fluctuations of the nematic director. This Casimir interaction decays as
d^(-6), d being the distance between the particles, and it dominates van der
Waals interactions close to the isotropic-to-nematic transition. Considering
the nematic as a polymer solvent, we show that the onset of this Casimir
interaction at the isotropic-to-nematic transition can discontinuously induce
the collapse of a flexible polymer chain from the swollen state to the globular
state, without crossing the Theta-point.


title:
Transport in a One-Dimensional Superfluid: Quantum Nucleation of Phase
  Slips

abstract:
  We present an analytical derivation for the quantum decay rate of the
superflow through a weak link in a one-dimensional Bose-Einstein-condensate.
The effective action for the phase difference across the link reduces to that
of a massive particle with damping subject to a periodic potential. We find an
algebraic flow-pressure relation, characteristic for quantum nucleation of
phase slips in the link and show how short-wave length fluctuations
renormalizing the interaction between the Bosons remove the quantum phase
transition expected in this class of systems.


title:
Influence of excited electron lifetimes on the electronic structure of
  carbon nanotubes

abstract:
  We have studied the dynamics of electrons in single wall carbon nanotubes
using femtosecond time-resolved photoemission. The lifetime of electrons
excited to the pi* bands is found to decrease continuously from 130 fs at 0.2
eV down to less than 20 fs at energies above 1.5 eV with respect to the Fermi
level. This should lead to a significant lifetime--induced broadening of the
characteristic van Hove singularities in the nanotube DOS.


title:
Finite-Temperature Transport in Finite-Size Hubbard Rings in the
  Strong-Coupling Limit

abstract:
  We study the current, the curvature of levels, and the finite temperature
charge stiffness, D(T,L), in the strongly correlated limit, U>>t, for Hubbard
rings of L sites, with U the on-site Coulomb repulsion and t the hopping
integral. Our study is done for finite-size systems and any band filling. Up to
order t we derive our results following two independent approaches, namely,
using the solution provided by the Bethe ansatz and the solution provided by an
algebraic method, where the electronic operators are represented in a
slave-fermion picture. We find that, in the U=\infty case, the
finite-temperature charge stiffness is finite for electronic densities, n,
smaller than one. These results are essencially those of spinless fermions in a
lattice of size L, apart from small corrections coming from a statistical flux,
due to the spin degrees of freedom. Up to order t, the Mott-Hubbard gap is
\Delta_{MH}=U-4t, and we find that D(T) is finite for n<1, but is zero at
half-filling. This result comes from the effective flux felt by the holon
excitations, which, due to the presence of doubly occupied sites, is
renormalized to
  \Phi^{eff}=\phi(N_h-N_d)/(N_d+N_h), and which is zero at half-filling, with
N_d and N_h being the number of doubly occupied and empty lattice sites,
respectively. Further, for half-filling, the current transported by any
eigenstate of the system is zero and, therefore, D(T) is also zero.


title: Generalized Exclusion Statistics in the Kondo Problem

abstract:
  We consider the generalized exclusion statistics in the Kondo problem. The
thermodynamic Bethe ansatz equations have been used for a multicomponent system
of particles obeying the generalized exclusion principle. We have found a
relation between the derivative of the phase shift of the scattering matrix for
Fermi particles and for particles characterized by generalized exclusion
statistics. We show that the statistical matrix in the Kondo problem has a
universal form in high and low temperature limits.


title:
Superconducting properties of Y_xLu_(1-x)Ni2B2C and La3Ni2B2N3: A
  comparison between experiment and Eliashberg theory

abstract:
  Specific heat and resistivity measurements were performed on polycrystalline
samples of the solid-solution Y_xLu_(1-x)Ni2B2C in order to determine
thermodynamic properties such as the specific-heat difference, the
thermodynamic critical field H_c(T), as well as the upper critical field
H_{c2}(T). These properties were analyzed within the Eliashberg theory
including anisotropy effects, yielding electron-phonon coupling anisotropy
parameters <a_k^2> ranging beween 0.02 and 0.03 for the whole series, and Fermi
velocity anisotropy parameters of <b_k^2> = 0.245-0.3. Excellent agreement
between theory and experiment was achieved for these parameters, the Sommerfeld
constant and model phonon spectra determined from specific heat measurements.
An analysis of the previously investigated boronitride La3Ni2B2N3 for
comparison revealed the electron-phonon anisotropy to be of great significance
in describing its thermodynamic properties and the calculations yielded <a_k^2>
\~ 0.08 and <b_k^2> ~ 0.245. The T_c-behavior within the series
Y_xLu_(1-x)Ni2B2C is discussed in terms of coupling and impurity effects, and
the density of states at the Fermi level N(0).


title:
Dynamics of inelastically colliding spheres with Coulomb friction:
  Relaxation of translational and rotational energy

abstract:
  We investigate the free cooling of inelastic rough spheres in the presence of
Coulomb friction. Depending on the coefficients of normal restitution
$\epsilon$ and Coulomb friction $\mu$, we find qualitatively different
asymptotic states. For nearly complete normal restitution ($\epsilon$ close to
1) and large $\mu$, friction does not change the cooling properties
qualitatively compared to a constant coefficient of tangential restitution. In
particular, the asymptotic state is characterized by a constant ratio of
rotational and translational energies, both decaying according to Haff's law.
However, for small $\epsilon$ and small $\mu$, the dissipation of rotational
energy is suppressed, so that the asymptotic state is characterized by constant
rotational energy while the translational energy continues to decay as
predicted by Haff's law. Introducing either surface roughness for grazing
collisions or cohesion forces for collisions with vanishing normal load, causes
the rotational energy to decay according to Haff's law again in the asymptotic
long-time limit with, however, an intermediate regime of approximately constant
rotational energy.


title:
Two-dimensional quantum interference contributions to the
  magnetoresistance of Nd{2-x}Ce{x}CuO{4-d} single crystals

abstract:
  The 2D weak localization effects at low temperatures T = (0.2-4.2)K have been
investigated in nonsuperconducting sample Nd{1.88}Ce{0.12}CuO{4-d} and in the
normal state of the superconducting sample Nd{1.82}Ce{0.18}CuO{4-d} for B>B_c2.
The phase coherence time and the effective thickness $d$ of a conducting CuO_2
layer have been estimated by the fitting of 2D weak localization theory
expressions to the magnetoresistivity data for the normal to plane and the
in-plane magnetic fields.


title: Response properties in a model for granular matter

abstract:
  We investigate the response properties of granular media in the framework of
the so-called {\em Random Tetris Model}. We monitor, for different driving
procedures, several quantities: the evolution of the density and of the density
profiles, the ageing properties through the two-times correlation functions and
the two-times mean-square distance between the potential energies, the response
function defined in terms of the difference in the potential energies of two
replica driven in two slightly different ways. We focus in particular on the
role played by the spatial inhomogeneities (structures) spontaneously emerging
during the compaction process, the history of the sample and the driving
procedure. It turns out that none of these ingredients can be neglected for the
correct interpretation of the experimental or numerical data. We discuss the
problem of the optimization of the compaction process and we comment on the
validity of our results for the description of granular materials in a
thermodynamic framework.


title: Coherent Evolution of Bouncing Bose-Einstein Condensates

abstract:
  We investigate the evolution of Bose-Einstein condensates falling under
gravity and bouncing off a mirror formed by a far-detuned sheet of light. After
reflection, the atomic density profile develops splitting and interference
structures which depend on the drop height, on the strength of the light sheet,
as well as on the initial mean field energy and size of the condensate. We
compare experimental results with simulations of the Gross-Pitaevski equation.
A comparison with the behaviour of bouncing thermal clouds allows to identify
quantum features specific for condensates.


title:
Self-consistent theory of shot noise in nondegenerate ballistic
  conductors

abstract:
  A self-consistent theory of shot noise in ballistic two-terminal conductors
under the action of long-range Coulomb correlations is presented. Analytical
formulas for the electron distribution function and its fluctuation along the
conductor, which account for the Coulomb correlations, have been derived. Based
upon these formulas, the current-noise reduction factor has been obtained for
biases ranging from thermal to shot-noise limits as dependent on two
parameters: the ratio between the length of the sample and the Debye screening
length \lambda=d/L_D and the applied voltage qU/k_BT. The difference with the
formulas for a vacuum diode is discussed.


title: Statistical Analysis of Freeway Traffic

abstract:
  Single-vehicle data of freeway traffic as well as selected Floating-Car (FC)
data are analyzed in great detail. Traffic states are distinguished by means of
aggregated data. We propose a method for a quantitative classification of these
states. The data of individual vehicles allows for insights into the
interaction of vehicles. The time-headway distribution reveals a characteristic
structure dominated by peaks and controlled by the underlying traffic states.
The tendency to reach a pleasant level of ``driving comfort'' gives rise to new
$v(\Delta x)$-diagrams, known as Optimal-Velocity (OV) curves. The insights
found at locally fixed detectors can be confirmed by FC data. In fundamental
diagrams derived from local measurements interesting high-flow states can be
observed.


title: A new cellular automata model for city traffic

abstract:
  We present a new cellular automata model of vehicular traffic in cities by
combining ideas borrowed from the Biham-Middleton-Levine (BML) model of city
traffic and the Nagel-Schreckenberg (NaSch) model of highway traffic. The model
exhibits a dynamical phase transition to a completely jammed phase at a
critical density which depends on the time periods of the synchronized signals.


title:
Implementation of an all-electron GW Approximation using the Projector
  Augmented Wave method: I. Formulation and application to the electronic
  structure of semiconductors

abstract:
  We have implemented the so called GW approximation (GWA) based on an
all-electron full-potential Projector Augmented Wave (PAW) method. For the
screening of the Coulomb interaction W we tested three different plasmon-pole
dielectric function models, and showed that the accuracy of the quasiparticle
energies is not sensitive to the the details of these models. We have then
applied this new method to compute the quasiparticle band structure of some
small, medium and large-band-gap semiconductors: Si, GaAs, AlAs, InP, SiMg$_2$,
C and (insulator) LiCl. A special attention was devoted to the convergence of
the self-energy with respect to both the {\bf k}-points in the Brillouin zone
and to the number of reciprocal space $\bf G$-vectors. The most important
result is that although the all-electron GWA improves considerably the
quasiparticle band structure of semiconductors, it does not always provide the
correct energy band gaps as originally claimed by GWA pseudopotential type of
calculations. We argue that the decoupling between the valence and core
electrons is a problem, and is some what hidden in a pseudopotential type of
approach.


title: Quantum Fluctuations and Dissipation in Thin Superconducting Wires

abstract:
  We investigate quantum fluctuations in thin superconducting wires. We
demonstrate that quantum phase slips dominate the system behavior at low
temperatures and are well in the measurable range for sufficiently thin wires.
We discuss the effect of dissipation, predict a new quantum
superconductor-to-metal (insulator) phase transitions for wires with
thicknesses in the 10-nm range, evaluate the resistance R(T) of such wires and
compare our results with recent experimental findings.


title:
Implementation of an all-electron GW Approximation using the Projector
  Augmented Wave method: II. Application to the optical properties of
  semiconductors

abstract:
  We used our previously implemented GW approximation (GWA) based on the
all-electron full-potential projector augmented wave (PAW) method to study the
optical properties of small, medium and large-band-gap semiconductors: Si,
GaAs, AlAs, InP, Mg$_2$Si, C, and LiCl. The aim being to study the size of both
local-field (LF) and the quasi-particle (QP) corrections to the calculated
dielectric function obtained using the local density approximation (LDA). We
found that while the QP corrections tend to align the calculated structures in
the optical spectra with their experimental counterparts, the LF effects don't
change these peak positions but systematically reduce the intensities of the so
called $E_1$ and $E_2$ structures in all the optical spectra. The reduction of
the intensity of the $E_1$ peak worsen the agreement with experiment while that
of $E_2$ improves it. We then show that the local-field correction improves
considerably the calculated static dielectric constants of all studied
semiconductors.
  Because the static dielectric constant is a ground state property, the
remaining discrepancy with experiment should be attributed to the the LDA
itself. On the other hand, as expected, the calculation of the static
dielectric constant using the GW quasiparticle energies and including the LF
effects is underestimated for all the semiconductors. The excitonic effects
should then correct for this discrepancy with experiment.


title: Interaction and Quantum Decoherence in Disordered Conductors

abstract:
  We present a nonperturbative approach which allows to evaluate the weak
localization correction to the conductivity of disordered conductors in the
presence of interactions. The effect of the electron-electron interaction on
the magnetoconductance is described by the function A(t)\exp (-f(t)). The
dephasing time is determined only by f(t), and this time remains finite down to
T=0 due to the electron-electron interactions. In order to establish the
relation between our nonperturbative analysis and the perturbative results the
effect of interaction on the pre-exponent A(t) should be taken into account.
The dephasing time cannot be unambiguously determined from a perturbative
calculation.


title:
Chaotic dynamics and superdiffusion in a Hamiltonian system with many
  degrees of freedom

abstract:
  We discuss recent results obtained for the Hamiltonian Mean Field model. The
model describes a system of N fully-coupled particles in one dimension and
shows a second-order phase transition from a clustered phase to a homogeneous
one when the energy is increased. Strong chaos is found in correspondence to
the critical point on top of a weak chaotic regime which characterizes the
motion at low energies. For a small region around the critical point, we find
anomalous (enhanced) diffusion and L\'evy walks in a transient temporal regime
before the system relaxes to equilibrium.


title: Shot noise suppression at 1D hopping

abstract:
  We have carried out a preliminary analysis of shot noise at hopping, focusing
on uniform 1D arrays of sites separated by N tunnel barriers. The results show
that at low temperatures the low-frequency density of the shot noise varies
from 1/N to 1 of the Schottky value, depending on the geometry, electron
density, and Coulomb interaction strength. An interesting feature is w^{-1/3}
dependence of the current spectral density at intermediate frequencies, which
reflects self-similarity of the fluctuations at different size scales.


title:
Extraction of Step-Repulsion Strengths from Terrace Width Distributions:
  Statistical and Analytic Considerations

abstract:
  Recently it has been recognized that the so-called generalized Wigner
distribution may provide at least as good a description of terrace width
distributions (TWDs) on vicinal surfaces as the standard Gaussian fit and is
particularly applicable for weak repulsions between steps, where the latter
fails. Subsequent applications to vicinal copper surfaces at various
temperatures confirmed the serviceability of the new analysis procedure but
raised some theoretical questions. Here we address these issues using
analytical, numerical, and statistical methods. We propose an extension of the
generalized Wigner distribution to a two-parameter fit that allows the terrace
widths to be scaled by an optimal effective mean width. We discuss
quantitatively the approach of a Wigner distribution to a Gaussian form for
strong repulsions, how errors in normalization or mean affect the deduced
interaction, and how optimally to extract the interaction from the variance and
mean of the TWD. We show that correlations reduce by two orders of magnitude
the number of {\em independent} measurements in a typical STM image. We also
discuss the effect of the discreteness ("quantization") of terrace widths,
finding that for high misorientation (small mean width) the standard continuum
analysis gives faulty estimates of step interactions.


title:
Antiferromagnetism and d-wave superconductivity in cuprates: a uster
  DMFT study

abstract:
  We present a new approach to investigate the coexistence of
antiferromagnetism and d-wave superconductivity in the two dimensional extended
Hubbard model within a numerically exact cluster dynamical mean-field
approximation. Self-consistent solutions with two non-zero order parameters
exists in the wide range of doping level and temperatures. A linearized
equation for energy spectrum near the Fermi level have been solved. The
resulting d-wave gap has the correct magnitude and k-dependence but some
distortion compare to the pure d_{x^2-y^2} superconducting order parameter due
to the presence of underlying antiferromagnetic ordering.


title: Commensurate and Incommensurate Spin Fluctuations in YBa_2Cu_3O_{6+y}

abstract:
  We present an interpretation of the recent neutron data on the commensurate
and incommensurate spin fluctuations found in YBa_2d$Cu_3O_{6+y} based on a
special configuration of the electronic dispersion and intervention from the
d_{x^2-y^2}-wave superconducting phase. The observed switch over between the
commensurate and incommensurate fluctuation spectra at the change of frequency
or temperature is naturally accounted within this scenario.


title: Spatial Particle Condensation for an Exclusion Process on a Ring

abstract:
  We study the stationary state of a simple exclusion process on a ring which
was recently introduced by Arndt {\it et al} [J. Phys. A {\bf 31} (1998)
L45;cond-mat/9809123]. This model exhibits spatial condensation of particles.
It has been argued that the model has a phase transition from a ``mixed phase''
to a ``disordered phase''. However, in this paper exact calculations are
presented which, we believe, show that in the framework of a grand canonical
ensemble there is no such phase transition. An analysis of the fluctuations in
the particle density strongly suggests that the same result also holds for the
canonical ensemble.


title: Rotational levels in quantum dots

abstract:
  Low energy spectra of isotropic quantum dots are calculated in the regime of
low electron densities where Coulomb interaction causes strong correlations.
The earlier developed pocket state method is generalized to allow for
continuous rotations. Detailed predictions are made for dots of shallow
confinements and small particle numbers, including the occurance of spin
blockades in transport.


title: Magnetic Phase Diagram of Weakly Pinned Type-II Superconductors

abstract:
  The phenomenon of superconductivity was discovered in 1911, however, the
methodology to classify and distinguish type-II superconductivity was
established only in late fifties after Abrikosov's prediction of a flux line
lattice in 1957. The advent of high temperature superconductors (HTSC) in 1986
focused attention onto identifying and classifying other possible phases of
vortex matter in all classes of superconductors by a variety of techniques. We
have collated evidences in support of a proposal to construct a generic phase
diagram for weakly pinned superconducting systems, based on their responses to
ac and dc magnetic fields. The phase diagram comprises quasi-glassy phases,
like, the Bragg glass, a vortex glass and a reentrant glass in addition to the
(completely) amorphous phases of pinned and unpinned variety. The
characteristic metastability and thermomagnetic history dependent features
recognized amongst various glassy vortex phases suggest close connections
between vortex matter and other disordered condensed matter systems, like, spin
glasses, super cooled liquids/ structural glasses, etc. A novel quenched random
disorder driven fracturing transition stands out amongst other noteworthy
facets of weakly vortex pinned vortex matter.


title:
The role of spin-orbit coupling for the superconducting state in
  Sr_2RuO_4

abstract:
  The odd-parity spin-triplet Cooper pairing states show a six-fold degeneracy
for a quasi-two-dimensional electron system. In this article we show how
spin-orbit coupling can lift this degeneracy for Sr_2RuO_4 taking the band
structure based on the three relevant t_{2g}-orbitals of the Ru-ions into
account. The stabilized state depends on the relative strength of the pairing
interaction. We show that under reasonable assumptions the chiral pairing state
d(k) = z(k_x +/- i k_y) is favored against the others.


title: Correlated sampling in quantum Monte Carlo: a route to forces

abstract:
  In order to find the equilibrium geometries of molecules and solids and to
perform ab initio molecular dynamics, it is necessary to calculate the forces
on the nuclei. We present a correlated sampling method to efficiently calculate
numerical forces and potential energy surfaces in diffusion Monte Carlo. It
employs a novel coordinate transformation, earlier used in variational Monte
Carlo, to greatly reduce the statistical error. Results are presented for
first-row diatomic molecules.


title: Exact ground state for 1D electronic models

abstract:
  We have found the exact ground state for two electronic models on a linear
chain. The first model describes half-filling electron system in the
ferromagnet--antiferromagnet transition point. In the singlet ground state the
spin correlators show giant spiral magnetic ordering with the period of a
spiral equals to the system size. The second electronic model describes the
point where the ground state has giant spiral off-diagonal long-range order
and, therefore, superconducting. We suggest the formation of the ground state
with giant spiral order (ferromagnetic or off-diagonal) as a probable scenario
of the subsequent destruction of the ferromagnetism and the superconductivity.


title: Computer simulation studies of wetting on heterogeneous surfaces

abstract:
  The wetting of solid surfaces by fluids is a problem of great practical
importance that has been extensively studied over the years. Most often, the
experimental work has involved measurements of the contact angle made by a
liquid on the solid surface of interest. Young's equation gives the relation
between the contact angle and the interfacial tensions. An alternative to the
contact angle computation is the more generally applicable formulation of this
problem based on simulations (and measurements) of adsorption isotherms for a
fluid on a weakly interacting solid surface. We present some GCMC computations
for the case of heterogeneous surfaces.


title: Charge Ordering in Organic ET Compounds

abstract:
  The charge ordering phenomena in quasi two-dimensional 1/4-filled organic
compounds (ET)_2X (ET=BEDT-TTF) are investigated theoretically for the $\theta$
and $\alpha$-type structures, based on the Hartree approximation for the
extended Hubbard models with both on-site and intersite Coulomb interactions.
It is found that charge ordered states of stripe-type are stabilized for the
relevant values of Coulomb energies, while the spatial pattern of the stripes
sensitively depends on the anisotropy of the models. By comparing the results
of calculations with the experimental facts, where the effects of quantum
fluctuation is incorporated by mapping the stripe-type charge ordered states to
the S=1/2 Heisenberg Hamiltonians, the actual charge patterns in the insulating
phases of $\theta$-(ET)_2MM'(SCN)_4 and $\alpha$-(ET)_2I_3 are deduced.
Furthermore, to obtain a unified view among the $\theta$, $\alpha$ and
$\kappa$-(ET)_2X families, the stability of the charge ordered state in
competition with the dimeric antiferromagnetic state viewed as the Mott
insulating state, which is typically realized in $\kappa$-type compounds, and
with the paramagnetic metallic state, is also pursued by extracting essential
parameters.


title: Non-Fermi Behavior of the Strongly Correlated Electron Systems

abstract:
  (1) The temperature dependence of the specific heat for a marginal Fermi
liquid has been calculated. (2) We calculated the self-energy at T=0 for a two
dimensional fermionic system with hyperbolic dispersion. The existence of the
saddle points in the energy gives rise to a marginal behavior. (3) We showed
that the two-dimensional fermionic system with the energy $\epsilon
_{\mathbf{k}}=k_xk_y$ has a non-Fermi behavior. (4) The electronic self-energy
due to the electron-spin interaction is calculated for a two dimensional
system. (5) We study the influence of the amplitude fluctuations of a non-Fermi
superconductor on the energy spectrum of the two-dimensional Anderson non-Fermi
system. (6) Using the field-theoretical methods we studied the evolution from
BCS theory to Bose-Einstein condensation (BEC) for a non-Fermi system. (7)
Using the renormalization group approach proposed by Millis we calculated the
specific heat coefficient $\gamma (T)$ for the magnetic fluctuations with
susceptibility $\chi^{-1}\sim \delta ^{\alpha}+| \omega | ^{\alpha}+f(q)$ near
a Lifshitz point.


title:
Masses of composite fermions carrying two and four flux quanta:
  Differences and similarities

abstract:
  This study provides a theoretical rationalization for the intriguing
experimental observation regarding the equality of the normalized masses of
composite fermions carrying two and four flux quanta, and also demonstrates
that the mass of the latter type of composite fermion has a substantial filling
factor dependence in the filling factor range $4/17 > \nu > 1/5$, in agreement
with experiment, originating from the relatively strong inter-composite fermion
interactions here.


title:
Defect configurations and dynamical behavior in a Gay-Berne nematic
  emulsion

abstract:
  To model a nematic emulsion consisting of a surfactant-coated water droplet
dispersed in a nematic host, we performed a molecular dynamics simulation of a
droplet immersed in a system of 2048 Gay-Berne ellipsoids in a nematic phase.
Strong radial anchoring at the surface of the droplet induced a Saturn ring
defect configuration, consistent with theoretical predictions for very small
droplets. A surface ring configuration was observed for lower radial anchoring
strengths, and a pair of point defects was found near the poles of the droplet
for tangential anchoring. We also simulated the falling ball experiment and
measured the drag force anisotropy, in the presence of strong radial anchoring
as well as zero anchoring strength.


title: Nonequilibrium Mesoscopic Conductors Driven by Reservoirs

abstract:
  In order to specify a nonequilibrium steady state of a quantum wire (QWR),
one must connect reservoirs to it. Since reservoirs should be large 2d or 3d
systems, the total system is a large and inhomogeneous 2d or 3d system, in
which e-e interactions have the same strength in all regions. However, most
theories of interacting electrons in QWR considered simplified 1d models, in
which reservoirs are absent or replaced with noninteracting 1d leads. We first
discuss fundamental problems of such theories in view of nonequilibrium
statistical mechanics. We then present formulations which are free from such
difficulties, and discuss what is going on in mesoscopic systems in
nonequilibrium steady state. In particular, we point out important roles of
energy corrections and non-mechanical forces, which are induced by a finite
current.

categories: cond-mat.mes-hall chao-dyn cond-mat.stat-mech nlin.CD


title:
Comments on "New representations of the Hecke algebra and algebraic
  Bethe Ansatz for an integrable generalized spin ladder", by H.-Q. Zhou, H.
  Frahm and M.D. Gould, cond-mat/9911072

abstract:
  The authors of cond-mat/9911072 claim to introduce "new representations of
the Hecke algebra." These representations are shown to be the XXC models
introduced two years ago in solv-int/9712008, and repeatedly studied and
referred to in subsequent papers. They are in fact representations of the
Temperley-Lieb algebra. Several other remarks are made and mistakes are pointed
out.


title: One-electron bands, quantum Monte Carlo, and real superconductors

abstract:
  We use the doped Fullerenes as an example of how realistic systems can be
described by simple models. Starting from the band structure we set up a
tight-binding model that describes the t_{1u} conduction band. Adding
correlation terms we arrive at a generalized Hubbard Hamiltonian that we treat
using quantum Monte Carlo. To address the problem of superconductivity in the
doped Fullerenes, we study the screening of a point charge. We find
surprisingly efficient metallic screening even for strong correlations, almost
up to the Mott transition, and discuss the implications on superconductivity,
in particular the effect of the efficient screening on the Coulomb
pseudopotential and the electron-phonon coupling.


title:
Two-fluid hydrodynamics of a Bose gas including damping from normal
  fluid transport coefficients

abstract:
  We extend our recent work on the two-fluid hydrodynamics of the condensate
and non-condensate in a trapped Bose gas by including the dissipation
associated with viscosity and thermal conduction. For purposes of illustration,
we consider the hydrodynamic modes in the case of a uniform Bose gas. A finite
thermal conductivity and shear viscosity give rise to a damping of the first
and second sound modes in addition to that found previously due to the lack of
diffusive equilibrium between the condensate and non-condensate. The
relaxational mode associated with this equilibration process is strongly
coupled to thermal fluctuations and reduces to the usual thermal diffusion mode
above the Bose-Einstein transition. In contrast to the standard Landau
two-fluid hydrodynamics, we predict a damped mode centered at zero frequency,
in addition to the usual second sound doublet.


title:
One-electron spectral functions of the attractive Hubbard model at
  intermediate coupling

abstract:
  We calculate the one-electron spectral function of the attractive-U Hubbard
model in two dimensions. We work in the intermediate coupling and low density
regime and evaluate analytically the self-energy. The results are obtained in a
framework based on the self-consistent T-matrix approximation. We also
calculate the chemical potential of the bound pairs as a function of
temperature. On the basis of this calculation we analyze the low-temperature
resistivity and specific heat in the normal state of this system. We compare
our results with recent beautiful tunneling experiments in the underdoped
regime of HTSC-materials.


title:
Domains growth and packing properties in driven granular media subject
  to gravity

abstract:
  We study the dynamical properties of recently introduced frustrated lattice
gas models (IFLG and Tetris) for granular media under gentle shaking. We
consider both the case where grains have inter-grain surface interactions and
the case where they have not, corresponding, for instance, to the presence or
absence of moisture in the packs. To characterise the grains packing structure,
we discuss the properties of density distribution. In particular, we consider
the phenomenon of grains domains formation under compaction. New results
amenable of experimental check are discussed along with some important
differences between the dynamics of the present models.


title: Quasiparticle energy spectrum in ferromagnetic Josephson weak links

abstract:
  The quasiparticles energy spectrum in clean ferromagnetic weak links between
conventional superconductors is calculated. Large peaks in DOS, due to a
special case of Andreev reflection at the ferromagnetic barrier, correspond to
spin-splitt bound states. Their energies are obtained as a function of the
barrier thickness, exchange field strength, and of the macroscopic phase
difference $\phi$ at the link, related to the Josephson current. In the ground
state, $\phi$ can be 0 or $\pi$, depending on the ferromagnetic barrier
influence. Conditions for the appearence of the zero-energy bound states (ZES)
and for the spin polarized ground state (SPGS) are obtained analytically. It is
shown that ZES appear only outside the weak link ground state.


title: A Particulate Basis for an Immiscible Lattice-Gas Model

abstract:
  We show that a phenomenological hydrodynamic lattice-gas model of two-phase
flow, developed by Rothman and Keller in 1988 and used extensively for
numerical simulations since then, can be derived from an underlying model of
particle interactions. From this result, we elucidate the nature of the
hydrodynamic limit of the Rothman-Keller model.


title:
The Penna model for biological ageing on a lattice: spatial consequences
  of child-care

abstract:
  We introduce a square lattice into the Penna bit-string model for biological
ageing and study the evolution of the spatial distribution of the population
considering different strategies of child-care. Two of the strategies are
related to the movements of a whole family on the lattice: in one case the
mother cannot move if she has any child younger than a given age, and in the
other case if she moves, she brings these young children with her. A stronger
condition has also been added to the second case, considering that young
children die with a higher probability if their mothers die, this probability
decreasing with age. We show that a highly non uniform occupation can be
obtained when child-care is considered, even for an uniform initial occupation
per site. We also compare the standard survival rate of the model with that
obtained when the spacial lattice is considered (without any kind of
child-care).


title: Surmounting Oscillating Barriers

abstract:
  Thermally activated escape over a potential barrier in the presence of
periodic driving is considered. By means of novel time-dependent path-integral
methods we derive asymptotically exact weak-noise expressions for both the
instantaneous and the time-averaged escape rate. The agreement with accurate
numerical results is excellent over a wide range of driving strengths and
driving frequencies.


title: Wetting at Non-Planar and Heterogeneous Substrates

abstract:
  We report results of wetting on non-planar and heterogeneous surfaces
calculated from an effective interfacial Hamiltonian model. The lack of
translational invariance along the substrate induces a series of structural
changes on the interface such as unbending and a number of non-thermodynamic
singularities and can modify the location of the wetting transition. We show
that the order of the wetting transition in the planar homogeneous system
strongly affects the behaviour of the non-planar and heterogeneous surfaces.


title:
Spinodal decomposition of off-critical quenches with a viscous phase
  using dissipative particle dynamics in two and three spatial dimensions

abstract:
  We investigate the domain growth and phase separation of
hydrodynamically-correct binary immiscible fluids of differing viscosity as a
function of minority phase concentration in both two and three spatial
dimensions using dissipative particle dynamics. We also examine the behavior of
equal-viscosity fluids and compare our results to similar lattice-gas
simulations in two dimensions.


title:
Characterization of localized hole states in
  Pr_(1+x)Ba_(2-x)Cu_(3)O_(6+y) by nuclear magnetic resonance

abstract:
  We investigated the charge distribution in
Pr_{1+x}Ba_{2-x}Cu_3O_{6+y}-crystals at liquid-He temperature by means of
^{63,65}Cu- and ^{141}Pr-NMR and NQR. The electric field gradients determined
for the different oxygen coordinations of Cu(1) on the chains confirm the model
that the hole states are localized in the O 2p - pi-orbitals of the
CuO_(2)-planes. The intensity and line-shape analysis of the Cu(1)- and
Pr-resonances in the oxygen doping series (x approx 0, y=0..1) and in the Pr/Ba
solid-solution series (at y=1) allows us to assign the Pr-resonance to Pr at
RE-sites. Therefore, we can investigate the charge distribution in the
CuO_(2)-Pr-CuO_(2)-layers by crystal field analysis of the Pr-signal. To
consistently describe our results with neutron scattering data we propose that
two Pr-states are present in the RE-layer, and ascribe them to Pr with and one
without a hole localized in the oxygen coordination shell. NMR detects only the
former, with a virtually nonmagnetic singlet ground state, while space-integral
techniques are dominated by the latter, due to a quasi-doublet ground state and
antiferromagnetism of its Pr-moments at low temperature.


title:
Ballistic aggregation: a solvable model of irreversible many particles
  dynamics

abstract:
  The adhesive dynamics of a one-dimensional aggregating gas of point particles
is rigorously described. The infinite hierarchy of kinetic equations for the
distributions of clusters of nearest neighbours is shown to be equivalent to a
system of two coupled equations for a large class of initial conditions. The
solution to these nonlinear equations is found by a direct construction of the
relevant probability distributions in the limit of a continuous initial mass
distribution. We show that those limiting distributions are identical to those
of the statistics of shocks in the Burgers turbulence. The analysis relies on a
mapping on a Brownian motion problem with parabolic constraints.


title: Charged stripes from alternating static magnetic field

abstract:
  We motivate and perform a calculation of the energy of a cold fluid of
charged fermions in the presence of a striped magnetic background. We find that
a non-trivial value for the doping density on the walls is preferred


title:
Response of non-equilibrium systems at criticality: Exact results for
  the Glauber-Ising chain

abstract:
  We investigate the non-equilibrium two-time correlation and response
functions and the associated fluctuation-dissipation ratio for the
ferromagnetic Ising chain with Glauber dynamics. The scaling behavior of these
quantities at low temperature and large times is studied in detail. This
analysis encompasses the self-similar domain-growth (aging) regime, the spatial
and temporal Porod regimes, and the convergence toward equilibrium. The
fluctuation-dissipation ratio admits a non-trivial limit value $X_\infty=1/2$
at zero temperature, and more generally in the aging regime.


title:
Parallel dynamics of the asymmetric extremely diluted Ashkin-Teller
  neural network

abstract:
  The parallel dynamics of the asymmetric extremely diluted Ashkin-Teller
neural network is studied using signal-to-noise analysis techniques. Evolution
equations for the order parameters are derived, both at zero and finite
temperature. The retrieval properties of the network are discussed in terms of
the four-spin coupling strength and the temperature. It is shown that the
presence of a four-spin coupling enhances the retrieval quality.


title:
Inelastic Light Scattering by Gap Excitations of Fractional Quantum Hall
  States at 1/3 <= \nu <= 2/3

abstract:
  We report observations of collective gap excitations of the fractional
quantum Hall (FQH) states at filling factors \nu=p/(2p+1) (p=integer), for 1/3
<= \nu <= 2/3, by inelastic light scattering. The collective gap energies at
\nu= 1/3, 2/5 and 3/7 show a drastic decrease as the value \nu =1/2 is
approached. These energies and the one at \nu=3/5 display the linear scaling
with (e^2/\epsilon l_o)/|2p+1| that is characteristic of composite fermions in
Chern-Simons gauge fields. In a narrow range of \nu centered at 1/2, where the
FQH gaps collapse, we observe a new excitation mode which exists only at
temperatures below 150 mK.


title:
Are Mean-Field Spin-Glass Models Relevant for the Structural Glass
  Transition?

abstract:
  We analyze the properties of the energy landscape of {\it finite-size} fully
connected p-spin-like models whose high temperature phase is described, in the
thermodynamic limit, by the schematic Mode Coupling Theory of super-cooled
liquids. We show that {\it finite-size} fully connected p-spin-like models,
where activated processes are possible, do exhibit properties typical of real
super-cooled liquid when both are near the critical glass transition. Our
results support the conclusion that fully-connected p-spin-like models are the
natural statistical mechanical models for studying the glass transition in
super-cooled liquids.


title: Finite size effect in the specific heat of YBa2Cu3O7-delta

abstract:
  We analyze high precision, high resolution microcalorimetric specific heat
data of detwinned YBa2Cu3O(7-delta) single crystals. It is shown that a finite
size effect must be taken into account when attempting to extract critical
properties. Contrary to previous claims, there is no contradiction to a regular
second order phase transition. Consistency with 3D-XY critical behavior is
demonstrated.


title:
Zero-Temperature Dynamics of Ising Spin Systems Following a Deep Quench:
  Results and Open Problems

abstract:
  We consider zero-temperature, stochastic Ising models with nearest-neighbor
interactions and an initial spin configuration chosen from a symmetric
Bernoulli distribution (corresponding physically to a deep quench). Whether a
final state exists, i.e., whether each spin flips only finitely many times as
time goes to infinity (for almost every initial spin configuration and
realization of the dynamics), or if not, whether every spin - or only a
fraction strictly less than one - flips infinitely often, depends on the nature
of the couplings, the dimension, and the lattice type. We review results,
examine open questions, and discuss related topics.


title:
A Microscopic Model of Ferroelectricity in Stress-free PbTiO3 Ultrathin
  Films

abstract:
  The ground-state polarization of PbTiO3 thin films is studied using a
microscopic effective Hamiltonian with parameters obtained from
first-principles calculations. Under short-circuit electrical boundary
conditions, (001) films with thickness as low as three unit cells are found to
have a perpendicularly polarized ferroelectric ground state with significant
enhancement of the polarization at the surface.


title:
Spectral and transport properties of doped Mott-Hubbard systems with
  incommensurate magnetic order

abstract:
  We present spectral and optical properties of the Hubbard model on a
two-dimensional square lattice using a generalization of dynamical mean-field
theory to magnetic states in finite dimension. The self-energy includes the
effect of spin fluctuations and screening of the Coulomb interaction due to
particle-particle scattering. At half-filling the quasiparticles reduce the
width of the Mott-Hubbard `gap' and have dispersions and spectral weights that
agree remarkably well with quantum Monte Carlo and exact diagonalization
calculations. Away from half-filling we consider incommensurate magnetic order
with a varying local spin direction, and derive the photoemission and optical
spectra. The incommensurate magnetic order leads to a pseudogap which opens at
the Fermi energy and coexists with a large Mott-Hubbard gap. The quasiparticle
states survive in the doped systems, but their dispersion is modified with the
doping and a rigid band picture does not apply. Spectral weight in the optical
conductivity is transferred to lower energies and the Drude weight increases
linearly with increasing doping. We show that incommensurate magnetic order
leads also to mid-gap states in the optical spectra and to decreased scattering
rates in the transport processes, in qualitative agreement with the
experimental observations in doped systems. The gradual disappearence of the
spiral magnetic order and the vanishing pseudogap with increasing temperature
is found to be responsible for the linear resistivity. We discuss the possible
reasons why these results may only partially explain the features observed in
the optical spectra of high temperature superconductors.


title: Treating some solid state problems with the Dirac equation

abstract:
  The ambiguity involved in the definition of effective-mass Hamiltonians for
nonrelativistic models is resolved using the Dirac equation. The multistep
approximation is extended for relativistic cases allowing the treatment of
arbitrary potential and effective-mass profiles without ordering problems. On
the other hand, if the Schrodinger equation is supposed to be used, our
relativistic approach demonstrate that both results are coincidents if the
BenDaniel and Duke prescription for the kinetic-energy operator is implemented.
Applications for semiconductor heterostructures are discussed.


title: Magnetic translations for a spatially periodic magnetic field

abstract:
  It is shown that in the case of free electron in a spatially periodic
magnetic field the concept of magnetic translations operators is still valid
and, moreover, these operators can be defined in the same way as for a Bloch
electron in a uniform magnetic field. The results can be a useful tool in
investigation of lately observed phenomena in 2DEG with spatially modulated
density.


title: Scanned Potential Microscopy of Edge States in a Quantum Hall Liquid

abstract:
  Using a low-temperature atomic force microscope as a local voltmeter, we
measure the Hall voltage profile in a quantum Hall conductor in the presence of
a gate-induced non-equilibrium edge state population at n=3. We observe sharp
voltage drops at the sample edges which are suppressed by re-equilibrating the
edge states.


title: The Role of Substrate Corrugations in Helium Monolayer Solidification

abstract:
  We investigate the first layer of helium adsorbed on graphite with
path-integral Monte Carlo, examining the role of substrate corrugations on the
phase diagram. When no corrugations are present, the equilibrium state of the
system is a liquid phase, with solidification occurring only under compression
but before layer promotion. We determine the solid-liquid coexistence region
and compare our results to recent Green's function Monte Carlo calculations on
the same system. When substrate corrugations are included, we find that the
equilibrium phase is the $\sqrt 3 \times \sqrt3$ commensurate solid phase that
is well known from experiment. The melting behavior, heat capacity, and single
particle binding energy are determined and compared to experiment. We further
find that for densities below the commensurate coverage, the low temperature
phase of the system consists of solid clusters in coexistence with coalesced
vacancies. We find no first layer liquid phase and so no superfluidity in this
layer, in contrast to some rather recent suggestions.


title:
Electrostatic Interaction between Long, Rigid Helical Macromolecules at
  All Interaxial Angles

abstract:
  We derive formulae for the electrostatic interaction between two long, rigid
macromolecules that may have arbitrary surface charge patterns and cross at an
arbitrary interaxial angle. We calculate the dependence of the interaction
energy on the interaxial angle, on the separation, and on the precise alignment
of the charge pattern on one molecule with respect to the other. We focus in
particular on molecules with helical charge patterns. We report an exact,
explicit expression for the energy of interaction between net-neutral helices
in a nonpolar medium as well as an approximate result for charged helices
immersed in an electrolyte solution. The latter result becomes exact in the
asymptotic limit of large separations. Molecular chirality of helices manifests
itself in a torque that tends to twist helices in a certain direction out of
parallel alignment and that has a nontrivial behavior at small interaxial
angles. We illustrate the theory with the calculation of the torque between
layers of idealized, DNA-like double helices in cholesteric aggregates. We
propose a mechanism of the observed cholesteric-to-columnar phase transition
and suggest an explanation for the observed macroscopic (0.4-5 um) pitch of the
cholesteric phase of B-DNA.


title:
First and second order ferromagnetic transition at T=0 in a 1D itinerant
  system

abstract:
  We consider a modified version of the one-dimensional Hubbard model, the
t1-t2 Hubbard chain, which includes an additional next-nearest-neighbor
hopping. It has been shown that at weak coupling this model has a Luttinger
liquid phase or a spin liquid phase depending upon the ratio of t2 to t1.
Additionally if the on-site interaction U is large enough, the ground state is
fully polarized. Using exact diagonalization and the density-matrix
renormalization group, we show that the transition to the ferromagnetic phase
is either of first or second order depending on whether the Luttinger liquid or
spin liquid is being destabilized. Since we work at T=0, the second order
transition is a quantum magnetic critical point.


title:
Semiclassical theory of excitonic polaritons in a planar semiconductor
  microcavity

abstract:
  We present a comprehensive theoretical description of quantum well
exciton-polaritons imbedded in a planar semiconductor microcavity. The exact
non-local dielectric response of the quantum well exciton is treated in detail.
The 4-spinor structure of the hole subband in the quantum well is considered,
including the pronounced band mixing effect. The scheme is self-contained and
can be used to treat different semiclassical aspects of the microcavity
properties. As an example, we analyze the "selection" rules for the
exciton-cavity mode coupling for different excitons.


title: New Spin-Wave Mode in Weak Ferromagnetic Fermi Liquids

abstract:
  We study a phenomenological model for weak ferromagnetic Fermi liquids and
investigate the properties of the spin waves in the model. The Landau kinetic
equation is used to derive, in addition to the known Goldstone mode, a new
spin-wave mode -- the first Silin-like ferromagnetic mode. We discuss the role
of the interaction parameter F^a_1 on the behavior of the Goldstone mode and
the first Silin-like ferromagnetic mode.


title:
Magnetization-plateau state of the S=3/2 spin chain with single ion
  anisotropy

abstract:
  We reexamine the numerical study of the magnetized state of the S=3/2 spin
chain with single ion anisotropy D(> 0) for the magnetization M=M_{S}/3, where
M_{S} is the saturation magnetization. We find at this magnetization that for
D<D_{c1}=0.387 the system is critical and the magnetization plateau does not
appear. For D > D_{c1}, the parameter region is divided into two parts D_{c1} <
D < D_{c2}=0.943 and D_{c2} < D. In each region, the system is gapful and the
M=M_{S}/3 magnetization plateau appears in the magnetization process. From our
numerical calculation, the intermediate region D_{c1} < D < D_{c2} should be
characterized by a magnetized valence-bond-solid state.


title:
Phase transition in the transverse Ising model using the extended
  coupled-cluster method

abstract:
  The phase transition present in the linear-chain and square-lattice cases of
the transverse Ising model is examined. The extended coupled cluster method
(ECCM) can describe both sides of the phase transition with a unified approach.
The correlation length and the excitation energy are determined. We demonstrate
the ability of the ECCM to use both the weak- and the strong-coupling starting
state in a unified approach for the study of critical behavior.


title:
Current patterns and magnetic impurities in time-reversal breaking
  superconductor

abstract:
  We study the impurity effect in the time reversal symmetry (${\cal T}$)
breaking superconductor based on the Bogoliubov-de Gennes (BdG) equations. In
${\cal T}$-violating superconductors, spontaneous currents are induced around
the impurity. The current patterns around the impurity reflect the structures
of the Cooper pairs. We investigate impurity problem numerically for two kinds
of ${\cal T}$ violating superconductors $(p_{x}\pm {\rm i}p_{y}$ and $d+{\rm
i}s)$ and investigate the currents around the impurity. We also study the
effects of the magnetic impurity in p-wave ($p_{x}\pm {\rm i}p_{y}$)
superconductor, especially in view of the zero-energy crossing of energy levels
related to the phase transition of the ground state.


title:
Magnetic phases near the Van Hove singularity in s- and d-band Hubbard
  model

abstract:
  We investigate the magnetic instabilities of the nondegenerate (s-band) and a
degenerate (d-band) Hubbard model in two dimensions using many-body effects due
to the particle-particle diagrams and Hund's rule local correlations. The
density of states and the position of Van Hove singularity change depending on
the value of next-nearest neighbor hopping t'. The Stoner parameter is strongly
reduced in the s-band case, and ferromagnetism survives only if electron
density is small, and the band is almost flat at small momenta due to
next-nearest neighbor hopping. In contrast, for the d-band case the reduction
of the Stoner parameter which follows from particle-particle correlations is
much smaller and ferromagnetism survives to a large extent. Inclusion of local
spin-spin correlations has a limited destabilizing effect on the magnetic
states.


title: Arrays of Josephson junctions in an environment with vanishing impedance

abstract:
  The Hamiltonian operator for an unbiased array of Josephson junctions with
gate voltages is constructed when only Cooper pair tunnelling and charging
effects are taken into account. The supercurrent through the system and the
pumped current induced by changing the gate voltages periodically are discussed
with an emphasis on the inaccuracies in the Cooper pair pumping.
Renormalisation of the Hamiltonian operator is used in order to reliably
parametrise the effects due to inhomogeneity in the array and non-ideal gating
sequences. The relatively simple model yields an explicit, testable prediction
based on three experimentally motivated and determinable parameters.


title:
Stimulated Bremsstrahlung in ElectronNucleus Scattering in a
  Multifrequency Electromagnetic Field

abstract:
  We theoretically investigate stimulated bremsstrahlung emission and
absorption (SBEA) in the scattering of a relativistic electron by a nucleus in
a multifrequency field of circularly polarized plane electromagnetic waves
propagating in the same direction. The general relativistic expression for the
SBEA probability is derived. It is demonstrated that the probability of
multiphoton SBEA involving an arbitrary number of waves is governed by the
functions, which depends on BunkinFedorov quantum parameters and quantum
interference parameters. We separate two substantially different kinematic
ranges in electron scattering: the BunkinFedorov range and the interference
range. In the interference range, we reveal a correlation between the numbers
of photons in all the waves. Due to this correlation, the total number of
photons emitted or absorbed by an electron (with allowance for the
polarizations of waves) is equal to zero. We analyze the cases of
nonrelativistic, relativistic, and ultrarelativistic electron energies. It is
demonstrated that the probability of multiphoton SBEA for an electron scattered
in the interference range may considerably exceed the corresponding probability
in the BunkinFedorov range.


title:
Influence of shear stress $\sigma_6$ on the phase transition and
  physical properties of KD2PO4 type ferroelectrics

abstract:
  Within the four-particle cluster approximation for the proton ordering model
we study the influence of shear stress $\sigma_6$ on the phase transition,
static dielectric, elastic and thermal properties of deuterated KD2PO4 type
ferroelectrics. Thermodynamic potentials and physical characteristics of the
crystals in the presence of stress $\sigma_6$ are calculated. Numerical
analysis of the obtained results is performed, and the set of the theory
parameters providing the best fit to the available experimental data is found.
The $Tc-\sigma_6$ phase diagram is constructed; temperature dependences of the
calculated quantities are studied, possible stress dependences are indicated.
Influence of $\sigma_6$ stress is analogous to that of electric field conjugate
to the order parameter.


title: Electronic-Transport Properties of Al-Cu-Fe Thin Films

abstract:
  Amorphous samples of Al-Cu-Fe were crystallized to the icosahedral phase
under the control of electrical conductivity and thermopower at a rather small
temperature of T=720 K. A comparison between different annealing states of the
amorphous and the resulting quasicrystalline phase done on the same sample
shows aston-ishing parallels in conductivity and large differences in
thermopower.


title:
Andreev scattering and conductance enhancement in mesoscopic
  semiconductor-superconductor junctions

abstract:
  An inherent difficulty in studying mesoscopic effects in
semiconductor--superconductor hybrid structures is the large Schottky barrier
which often forms at the interface. A large technological effort has been
invested in in improving the contact between the superconductor and the
two-dimensional electron gas (2DEG) of a semiconductor heterostructure, and in
recent years this has become possible for e.g. GaAs-Al, GaAs-In, and InAs-Nb
junctions. This development motivates quantitative theoretical modeling of
sample-specific transport properties. The aim of our work is to model the
conducting properties of a ballistic 2DEG-S interfaces with a QPC in the normal
region and also to take into account scattering due to a weak Schottky barrier
and/or non-matching Fermi properties of the semiconductor and superconductor.


title:
Fabrication of High Quality QC Films via the Route of the Amorphous
  Phase

abstract:
  We discuss the preparation of thin icosahedral films (Al-Cu-Fe and Al-Pd-Re)
via the route of the amorphous (a-)phase which in some aspects is a precursor
to the icosahedral phase. A direct transition from the a- to the i-phase occurs
for Al-Cu-Fe films at 430 C on the time scale of minutes. The resulting films
are of good quality as shown by diffraction and electronic transport
properties. The surface of the resulting films is very smooth.


title:
Monopole, half-quantum vortices and nexus in chiral superfluids and
  superconductors

abstract:
  Two exotic objects are still not identified experimentally in chiral
superfluids and superconductors. These are the half-quantum vortex, which plays
the part of the Alice string in relativistic theories, and the hedgehog in the
l-field, which is the counterpart of the Dirac magnetic monopole. These two
objects of different dimensionality are topologically connected. They form the
combined object which is called nexus in relativistic theories
(hep-th/9911125). Such combination will allow us to observe half-quantum
vortices and monopoles in several realistic geometries.


title: Fluctuation-Stimulated Variable-Range Hopping

abstract:
  Qualitatively new transport mechanism is suggested for hopping of carriers
according to which the variable-range hopping (VRH) arises from the resonant
tunneling between transport states brought into resonance by Coulomb potentials
produced by surrounding sites with fluctuating occupations. A semiquantitative
description of the hopping transport is given based on the assumption that
fluctuations of energies of hopping sites have spectral density 1/f.


title: Green's and spectral functions of the small Frolich polaron

abstract:
  According to recent Quantum Monte Carlo simulations the small polaron theory
is practically exact in a wide range of the long-range (Frohlich)
electron-phonon coupling and adiabatic ratio. We apply the Lang-Firsov
transformation to convert the strong-coupling term in the Hamiltonian into the
form of an effective hopping integral and derive the single-particle Green's
function describing propagation of the small Frohlich polaron. One and two
dimensional spectral functions are studied by expanding the Green's function
perturbatively. Numerical calculations of the spectral functions are produced.
Remarkably, the coherent spectral weight (Z) and effective mass (Z')
renormalisation exponents are found to be different with Z'>>Z, which can
explain a small coherent spectral weight and a relatively moderate mass
enhancement in oxides.


title:
Collisionless dynamics of dilute Bose gases: Role of quantum and thermal
  fluctuations

abstract:
  We study the low-energy collective oscillations of a dilute Bose gas at
finite temperature in the collisionless regime. By using a time-dependent
mean-field scheme we derive for the dynamics of the condensate and
noncondensate components a set of coupled equations, which we solve
perturbatively to second order in the interaction coupling constant. This
approach is equivalent to the finite-temperature extension of the Beliaev
approximation and includes corrections to the Gross-Pitaevskii theory due both
to quantum and thermal fluctuations. For a homogeneous system we explicitly
calculate the temperature dependence of the velocity of propagation and damping
rate of zero sound. In the case of harmonically trapped systems in the
thermodynamic limit, we calculate, as a function of temperature, the frequency
shift of the low-energy compressional and surface modes.


title: Disordered Hubbard model in $d=\infty$

abstract:
  We investigate the effects of static, diagonal disorder in the $d=\infty$
Hubbard model by treating the dynamical effects of local Hubbard correlations
and disorder on an equal footing. This is achieved by a proper combination of
the iterated perturbation theory and the coherent potential approximation.
Within the paramagnetic phase, we find that the renormalized Fermi liquid metal
phase of the pure Hubbard model is stable against disorder for small disorder
strengths. With increasing disorder, strong resonant scattering effects destroy
low-energy Fermi liquid coherence, leading to an {\it incoherent} metallic
non-FL state off half-filling. Finally, for large enough disorder, a {\it
continuous} transition to the Mott-Anderson insulating phase occurs. The nature
of the non-FL metallic phase, as well as the effects of the low energy
coherence (incoherence) on optical conductivity and electronic Raman spectra,
are considered in detail.


title: Interacting Topological Defects on Frozen Topographies

abstract:
  We propose and analyze an effective free energy describing the physics of
disclination defects in particle arrays constrained to move on an arbitrary
two-dimensional surface. At finite temperature the physics of interacting
disclinations is mapped to a Laplacian Sine-Gordon Hamiltonian suitable for
numerical simulations. We then specialize to the case of a spherical crystal at
zero temperature. The ground state is analyzed as a function of the ratio of
the defect core energy to the Young's modulus. We argue that the core energy
contribution becomes less and less important in the limit R >> a, where R is
the radius of the sphere and a is the particle spacing. For large core energies
there are twelve disclinations forming an icosahedron. For intermediate core
energies unusual finite-length grain boundaries are preferred. The complicated
regime of small core energies, appropriate to the limit R/a goes to infinity,
is also addressed. Finally we discuss the application of our results to the
classic Thomson problem of finding the ground state of electrons distributed on
a two-sphere.


title:
Charge ordering and long-range interactions in layered transition metal
  oxides: a quasiclassical continuum study

abstract:
  The competition between long-range and short-range interactions among holes
moving in an antiferromagnet (AF), is studied within a model derived from the
spin density wave picture of layered transition metal oxides. A novel numerical
approach is developed which allows one to solve the problem at finite hole
densities in very large systems (of order hundreds of lattice spacings), albeit
in a quasiclassical limit, and to correctly incorporate the long-range part of
the Coulomb interaction. The focus is on the problem of charge ordering and the
charge phase diagram: at low temperatures four different phases are found,
depending on the strength of the magnetic (dipolar) interaction generated by
the spin-wave exchange, and the density of holes. The four phases are the
Wigner crystal, diagonal stripes, a grid phase (horizontal-vertical stripe
loops) and a glassy-clumped phase. In the presence of both in-plane and
out-of-plane charged impurities the stripe ordering is suppressed, although
finite stripe segments persist. At finite temperatures multiscale
(intermittency) dynamics is found, reminiscent of that in glasses. The dynamics
of stripe melting and its implications for experiments is discussed.


title:
Cerenkov generation of high-frequency confined acoustic phonons in
  quantum wells

abstract:
  We analyze the Cerenkov emission of high-frequency confined acoustic phonons
by drifting electrons in a quantum well. We find that the electron drift can
cause strong phonon amplification (generation). A general formula for the gain
coefficient, alpha, is obtained as a function of the phonon frequency and the
structure parameters. The gain coefficient increases sharply in the short-wave
region. For the example of a Si/SiGe/Si device it is shown that the
amplification coefficients of the order of hundreds of 1/cm can be achieved in
the sub-THz frequency range.


title:
The First Synchrotron Infrared Beamlines at the ALS: Spectromicroscopy
  and Fast Timing

abstract:
  Two recently commissioned infrared beamlines on the 1.4 bending magnet port
at the Advanced Light Source, LBNL, are described. Using a synchrotron as an IR
source provides three primary advantages: increased brightness, very fast light
pulses, and enhanced far-IR flux. The considerable brightness advantage
manifests itself most beneficially when performing spectroscopy on a
microscopic length scale. Beamline (BL) 1.4.3 is a dedicated FTIR
spectromicroscopy beamline, where a diffraction-limited spot size using the
synchrotron source is utilized. BL 1.4.2 consists of a vacuum FTIR bench with a
wide spectral range and step-scan capability. This BL makes use of the pulsed
nature of the synchrotron light as well as the far-IR flux. Fast timing is
demonstrated by observing the pulses from the electron bunch storage pattern at
the ALS. Results from several experiments from both IR beamlines will be
presented as an overview of the IR research currently being done at the ALS.

categories: cond-mat.mtrl-sci cond-mat.str-el physics.bio-ph physics.optics


title: Potts model: Duality, Uniformization and the Seiberg-Witten modulus

abstract:
  The introduction of a modulus z(K), analogous to u=<tr phi^2> in the N=2 SUSY
SU(2) gauge theory solved by Seiberg and Witten, and whose defining property is
the invariance under the symmetry and duality transformations of the effective
coupling K, reveals an intriguing correspondence between the D=2 Ising and
Potts models on the square lattice. The moduli spaces of both models, the
spaces of inequivalent effective temperatures K, correspond to a
three-punctured sphere M_3=P^1(C)\{z=+1,-1,\infty}. Furthermore, in both
models, the locus of Fisher zeroes is given by the segment joining z_c=-1 to
z_c=+1.


title:
Crystallization and phase-separation in non-additive binary hard-sphere
  mixtures

abstract:
  We calculate for the first time the full phase-diagram of an asymmetric
non-additive hard-sphere mixture. The non-additivity strongly affects the
crystallization and the fluid-fluid phase-separation. The global topology of
the phase-diagram is controlled by an effective size-ratio y_{eff}, while the
fluid-solid coexistence scales with the depth of the effective potential well.


title:
Phase diagram of the one-dimensional extended attractive Hubbard model
  for large nearest-neighbor repulsion

abstract:
  We consider the extended Hubbard model with attractive on-site interaction U
and nearest-neighbor repulsions V. We construct an effective Hamiltonian
H_{eff} for hopping t<<V and arbitrary U<0. Retaining the most important terms,
H_{eff} can be mapped onto two XXZ models, solved by the Bethe ansatz. The
quantum phase diagram shows two Luttinger liquid phases and a region of phase
separation between them. For density n<0.422 and U<-4, singlet superconducting
correlations dominate at large distances. For some parameters, the results are
in qualitative agreement with experiments in BaKBiO.


title: Asymmetric exclusion process and extremal statistics of random sequences

abstract:
  An exact mapping is established between sequence alignment, one of the most
commonly used tools of computational biology, and the asymmetric exclusion
process, one of the few exactly solvable models of nonequilibrium physics. The
statistical significance of sequence alignments is characterized through
studying the total hopping current of the discrete time and space version of
the asymmetric exclusion process.


title: Magnetization plateaux in dimerized spin ladder arrays

abstract:
  We investigate the ground state magnetization plateaux appearing in spin 1/2
two-leg ladders built up from dimerized antiferromagnetic Heisenberg chains and
dimerized zig-zag interchain couplings. Using both Abelian bosonization and
Lanczos methods we find that the system yields rather unusual plateaux and
exhibits massive and massless phases for specific choices or ``tuning'' of
exchange interactions. The relevance of this behavior in the study of
NH_4CuCl_3 is discussed.


title: Survival Probabilities for Discrete Time Models in One Dimension

abstract:
  We consider survival probabilities for the discrete time process in one
dimension, which is known as the Domany-Kinzel model. A convergence theorem for
infinite systems can be obtained in the nonattractive case.


title:
Josephson Current Flowing in Cyclically Coupled Bose-Einstein
  Condensates

abstract:
  The Josephson effect in cyclically coupled Bose-Einstein condensates is
studied theoretically. We analyze the simultaneous Gross-Pitaevskii equations
with coupling terms between adjacent condensates. Depending on the initial
relative phases between condensates, Josephson current flows cyclically to make
a quantized vortex. Reducing the coupling between condensates changes the
motion from periodic to chaotic, thus suppressing the cyclic current. The
relation to the Kibble-Zurek mechanism is discussed.


title:
Density-Matrix approach to a Strongly Coupled Two-Component
  Bose-Einstein Condensate

abstract:
  The time evolution equations for average values of population and relative
phase of a strongly coupled two component BEC is derived analytically. The two
components are two hyper-fine states coupled by an external laser that drives
fast Rabi oscillations between these states. Specifically, this derivation
incorporates the two-mode model proposed in [1] for the strongly coupled
hyper-fine states of Rb. The fast Rabi cycle is averaged out and rate equations
are derived that represents the slow dynamics of the system. These include the
collapse and revival of Rabi oscillations and their subsequent dependence on
detuning and trap displacement as reported in experiments of [1]. A proposal to
create stable vortices is also given.


title:
Topological phase preparation in a pair of atomic Bose-Einstein
  condensates

abstract:
  We propose a method of generating skyrmion vortices in a pair of
Bose-Einstein condensates occupying two internal states of the same atom. We
show that a variety of different periodic arrays of vortices may be prepared
with an appropriate superposition of orthogonal standing electromagnetic waves
inducing a coherent coupling between the two condensates.


title: Conformal Algebras of 2D Disordered Systems

abstract:
  We discuss the structure of 2D conformal field theories (CFT) at central
charge c=0 describing critical disordered systems, polymers and percolation. We
construct a novel extension of the c=0 Virasoro algebra, characterized by a
number b measuring the effective number of massless degrees of freedom, and by
a logarithmic partner of the stress tensor. It is argued to be present at a
generic random critical point, lacking super Kac-Moody, or other higher
symmetries, and is a tool to describe and classify such theories.
Interestingly, this algebra is not only consistent with, but indeed naturally
accommodates in general an underlying global supersymmetry. Polymers and
percolation realize this algebra. Unexpectedly, we find that the c=0 Kac table
of the degenerate fields contains two distinct theories with b=5/6 and b=-5/8
which we conjecture to correspond to percolation and polymers respectively. A
given Kac-table field can be degenerate only in one of them. Remarkably, we
also find this algebra, and thereby an ensuing hidden supersymmetry, realized
at general replica-averaged critical points, for which we derive an explicit
formula for b.

categories: cond-mat.dis-nn cond-mat.mes-hall cond-mat.stat-mech hep-th


title:
Numerical Model for Calculating the Field Dependence of the Irreversible
  Magnetisation of Hard Ssuperconductors in High Pulsed Magnetic Fields

abstract:
  In type II hard superconductors the irreversible magnetization shows an
impressive variety of different magnetic field dependencies. In this paper we
will try to describe the M(H) relation at fixed temperature To by a numerical
model in which we incorporate two features: the magnetic and electric field
dependency of the local critical current density j(To,H,E). The electric field
is determined by the magnetic field sweep rate; in effect E ~ dB/dt. We
confront the model with experimental pulsed field magnetization measurements
(PFMM) on a fast melt processed YBa2Cu3O7 sample.


title:
Exactly solvable spin ladder model with degenerate ferromagnetic and
  singlet states

abstract:
  We study the spin ladder model with interactions between spins on neighboring
rungs. The model Hamiltonian with the exact singlet ground state degenerated
with ferromagnetic state is obtained. The singlet ground state wave function
has a special recurrent form and depends on two parameters. Spin correlations
in the singlet ground state show double-spiral structure with period of spirals
equals to the system size. For special values of parameters they have
exponential decay. The spectrum of the model is gapless and there are
asymptotically degenerated excited states for special values of parameters in
the thermodynamic limit.


title:
Suppression of non-Poissonian shot noise by Coulomb correlations in
  ballistic conductors

abstract:
  We investigate the current injection into a ballistic conductor under the
space-charge limited regime, when the distribution function of injected
carriers is an arbitrary function of energy F_c(epsilon). The analysis of the
coupled kinetic and Poisson equations shows that the injected current
fluctuations may be essentially suppressed by Coulomb correlations, and the
suppression level is determined by the shape of F_c(epsilon). This is in
contrast to the time-averaged quantities: the mean current and the spatial
profiles are shown to be insensitive to F_c(epsilon) in the leading-order terms
at high biases. The asymptotic high-bias behavior for the energy resolved
shot-noise suppression has been found for an arbitrary (non-Poissonian)
injection, which may suggest a new field of investigation on the optimization
of the injected energy profile to achieve the desired noise-suppression level.


title: Zero-variance principle for Monte Carlo algorithms

abstract:
  We present a general approach to greatly increase at little cost the
efficiency of Monte Carlo algorithms. To each observable to be computed we
associate a renormalized observable (improved estimator) having the same
average but a different variance. By writing down the zero-variance condition a
fundamental equation determining the optimal choice for the renormalized
observable is derived (zero-variance principle for each observable separately).
We show, with several examples including classical and quantum Monte Carlo
calculations, that the method can be very powerful.


title:
Orientational transition in nematic liquid crystals under oscillatory
  Poiseuille flow

abstract:
  We investigate the orientational behaviour of a homeotropically aligned
nematic liquid crystal subjected to an oscillatory plane Poiseuille flow
produced by an alternating pressure gradient. For small pressure amplitudes the
director oscillates within the flow plane around the initial homeotropic
position, whereas for higher amplitudes a spatially homogeneous transition to
out-of-plane director motion was observed for the first time. The orientational
transition was found to be supercritical and the measured frequency dependence
of the critical pressure amplitude in the range between 2 and 20 Hz was in
quantitative agreement with a recent theory.