title: Supercooled Liquids and Glasses

abstract:
  In these lectures, which were presented at "Soft and Fragile Matter,
Nonequilibrium Dynamics, Metastability and Flow" University of St. Andrews, 8
July - 22 July, 1999, I give an introduction to the physics of supercooled
liquids and glasses and discuss some computer simulations done to investigate
these systems.


title: Logarithmic Correlations in Quenched Random Magnets and Polymers

abstract:
  It is argued that logarithmic factors multiplying power law behavior are to
be expected at or near non-mean field critical points of systems with
short-range interactions described theoretically by any kind of n -> 0 limit,
in which the effective free energy vanishes. Explicit examples are given for
quenched random ferromagnets, polymer statistics and percolation, but the
phenomenon is quite general.


title: Non equilibrium mode coupling theory for supercooled liquids and glasses

abstract:
  A formally exact set of equations is derived for the description of
nonequilibrium phenomena in classical liquids and glasses. With the help of a
non equilibrium projection operator formalism, the correlation functions and
fluctuation propagators are expressed in terms of memory functions and time
dependent collective frequencies. This formally exact set of equations is
approximated by applying mode coupling approximations to the memory functions.
The resulting set of equations for wavevector dependent correlation functions,
fluctuation propagators and one-time structure factors $S_q(t)$ generalizes the
well known mode coupling theory of the glass transition to situations far away
from equilibrium.


title:
Superconductivity and Magnetism at Nuclear-matter Densities: An
  Astronomical Challenge

abstract:
  We report on a study of the evolution of magnetic fields of neutron stars,
driven by the expulsion of magnetic flux out of the proton superconducting core
of the star. The rate of expulsion, or equivalently the velocity of outward
motion of flux-carrying proton-vortices is determined from a solution of their
equation of motion. A determination of the effective forces on the fluxoids
moving through the quantum liquid interior of neutron stars is however
confronted with many ambiguities about the properties of this special case of
superconductivity in the nature. Also, the behaviour of the fluxoids at the
core boundary, and the subsequent evolution of the expelled flux within the
highly conductive surrounding crust, are other related issues that have not
been so far explored in any great details.


title: On the use of non-canonical quantum statistics

abstract:
  We develop a method using a coarse graining of the energy fluctuations of an
equilibrium quantum system which produces simple parameterizations for the
behaviour of the system. As an application, we use these methods to gain more
understanding on the standard Boltzmann-Gibbs statistics and on the recently
developed Tsallis statistics. We conclude on a discussion of the role of
entropy and the maximum entropy principle in thermodynamics.


title:
The generalized Kramers' theory for nonequilibrium open one-dimensional
  systems

abstract:
  The Kramers' theory of activated processes is generalized for nonequilibrium
open one-dimensional systems. We consider both the internal noise due to
thermal bath and the external noise which are stationary, Gaussian and are
characterized by arbitrary decaying correlation functions. We stress the role
of a nonequilibrium stationary state distribution for this open system which is
reminiscent of an equilibrium Boltzmann distribution in calculation of rate.
The generalized rate expression we derive here reduces to the specific limiting
cases pertaining to the closed and open systems for thermal and non-thermal
steady state activation processes.


title:
Critical properties of the metal-insulator transition in anisotropic
  systems

abstract:
  We study the three-dimensional Anderson model of localization with
anisotropic hopping, i.e., weakly coupled chains and weakly coupled planes. In
our extensive numerical study we identify and characterize the metal-insulator
transition by means of the transfer-matrix method. The values of the critical
disorder $W_c$ obtained are consistent with results of previous studies,
including multifractal analysis of the wave functions and energy level
statistics. $W_c$ decreases from its isotropic value with a power law as a
function of anisotropy. Using high accuracy data for large system sizes we
estimate the critical exponent as $\nu=1.62\pm0.07$. This is in agreement with
its value in the isotropic case and in other models of the orthogonal
universality class.


title:
Long-range interacting rotators: connection with the mean--field
  approximation

abstract:
  We analyze the equilibrium properties of a chain of ferromagnetically coupled
rotators which interact through a force that decays as $r^{-\alpha}$ where r is
the interparticle distance and $\alpha\ge 0$. Our model contains as particular
cases the mean field limit ($\alpha=0$) and the first-neighbor model ($\alpha
\to \infty$). By integrating the equations of motion we obtain the
microcanonical time averages of both the magnetization and the kinetic energy.
Concerning the long-range order, we detect three different regimes at low
energies, depending on whether $\alpha$ belongs to the intervals $[0,1)$,
$(1,2)$ or $(2,\infty)$. Moreover, for $0 \le \alpha < 1$, the microcanonical
averages agree, after a simple scaling, with those obtained in the canonical
ensemble for the mean-field XY model. This correspondence offers a
mathematically tractable and computationally economic way of dealing with
systems governed by slowly decaying long-range interactions.


title: Manifold self-localization in a deformable medium

abstract:
  Directed manifolds (domain walls, interfaces, vortex lines) in a deformable
medium can exist in a correlated state in which the manifold is self-localized
by its own strain field. Depending on the temperature, manifold/medium
dimensionalities, and the strength of the coupling with the medium, the degree
of localization of the ground state can vary both continuously and
discontinuously; there can be phase transitions from self- localized to the
free-manifold state.


title:
The statistics of velocity fluctuations arising from a random
  distribution of point vortices: the speed of fluctuations and the diffusion
  coefficient

abstract:
  This paper is devoted to a statistical analysis of the fluctuations of
velocity and acceleration produced by a random distribution of point vortices
in two-dimensional turbulence. We show that the velocity probability density
function (p.d.f.) behaves in a manner which is intermediate between Gaussian
and L\'evy laws while the distribution of accelerations is governed by a Cauchy
law. Our study accounts properly for a spectrum of circulations among the
vortices. In the case of real vortices (with a finite core) we show
analytically that the distribution of accelerations makes a smooth transition
from Cauchy (for small fluctuations) to Gaussian (for large fluctuations)
passing probably through an exponential tail. We introduce a function $T(V)$
which gives the typical duration of a velocity fluctuation $V$; we show that
$T(V)$ behaves like $V$ and $V^{-1}$ for weak and large velocities
respectively. These results have a simple physical interpretation in the
nearest neighbor approximation and in Smoluchowski theory concerning the
persistence of fluctuations. We discuss the analogies with respect to the
fluctuations of the gravitational field in stellar systems. As an application
of these results, we determine an approximate expression for the diffusion
coefficient of point vortices. When applied to the context of freely decaying
two-dimensional turbulence, the diffusion becomes anomalous and we establish a
relationship $\nu=1+{\xi\over 2}$ between the exponent of anomalous diffusion
$\nu$ and the exponent $\xi$ which characterizes the decay of the vortex
density. This relation is in good agreement with laboratory experiments and
numerical simulations.

categories: cond-mat.stat-mech chao-dyn nlin.CD physics.flu-dyn


title: Flux pinning by regular arrays of ferromagnetic dots

abstract:
  The pinning of flux lines by two different types of regular arrays of
submicron magnetic dots is studied in superconducting Pb films; rectangular Co
dots with in-plane magnetization are used as pinning centers to investigate the
influence of the magnetic stray field of the dots on the pinning phenomena,
whereas multilayered Co/Pt dots with out-of-plane magnetization are used to
study the magnetic interaction between the flux lines and the magnetic moment
of the dots. For both types of pinning arrays, matching anomalies are observed
in the magnetization curves versus perpendicular applied field at integer and
rational multiples of the first matching field, which correspond to stable flux
configurations in the artificially created pinning potential. By varying the
magnetic domain structure of the Co dots with in-plane magnetization, a clear
influence of the stray field of the dots on the pinning efficiency is found.
For the Co/Pt dots with out-of-plane magnetization, a pronounced field
asymmetry is observed in the magnetization curves when the dots are magnetized
in a perpendicular field prior to the measurement. This asymmetry can be
attributed to the interaction of the out-of-plane magnetic moment of the Co/Pt
dots with the local field of the flux lines and indicates that flux pinning is
stronger when the magnetic moment of the dot and the field of the flux line
have the same polarity.


title:
Magnetic properties of submicron Co islands and their use as artificial
  pinning centers

abstract:
  We report on the magnetic properties of elongated submicron magnetic islands
and their influence on a superconducting film. The magnetic properties were
studied by magnetization hysteresis loop measurements and scanning-force
microscopy. In the as-grown state, the islands have a magnetic structure
consisting of two antiparallel domains. This stable domain configuration has
been directly visualized as a 2x2-checkerboard pattern by magnetic-force
microscopy. In the remanent state, after magnetic saturation along the easy
axis, all islands have a single-domain structure with the magnetic moment
oriented along the magnetizing field direction. Periodic lattices of these Co
islands act as efficient artificial pinning arrays for the flux lines in a
superconducting Pb film deposited on top of the Co islands. The influence of
the magnetic state of the dots on their pinning efficiency is investigated in
these films, before and after the Co dots are magnetized.


title: Possible Existence of an Extraordinary Phase in the Driven Lattice Gas

abstract:
  We report recent simulation results which might indicate the existence of a
new low-temperature "phase" in an Ising lattice gas, driven into a
non-equilibrium steady state by an external field. It appears that this
"phase", characterized by multiple-strip configurations, is selected when
square systems are used to approach the thermodynamic limit. We propose a
quantitative criterion for the existence of such a "phase". If confirmed, its
observation may resolve a long-standing controversy over the critical
properties of the driven Ising lattice gas.


title: A Model for Double-Stranded Excitations of DNA

abstract:
  We calculate the spectrum of torsional vibrations of a double-stranded
structure that models the double helix of the DNA. We come to the conclusion
that within the framework of the model elementary excitations may display an
asymmetry as regards their winding and direction of the propagation, depending
on initial polarization. The asymmetry could have a bearing on processes that
take place in molecules of the DNA.


title:
Does the Heisenberg model describe the multimagnon spin dynamics in
  antiferromagnetic CuO layers ?

abstract:
  We compute the absorption spectrum for multimagnon excitations assisted by
phonons in insulating layered cuprates using exact diagonalization in clusters
of up to 32 sites. The resulting line shape is very sensitive to the underlying
magnetic Hamiltonian describing the spin dynamics. For the usual Heisenberg
description of undoped Cu-O planes we find, in accordance with experiment, a
two-magnon peak followed by high energy side bands. However the relative weight
of the side bands is too small to reproduce the experiment. An extended
Heisenberg model including a sizable four-site cyclic exchange term is shown to
be consistent with the experimental data.


title: Sound attenuation in the superconducting amorphous alloy ZrTiCuNiBe

abstract:
  The superconducting energy gap and the parameter of the intensity of electron
scattering at two-level systems in amorphous ZrTiCuNiBe are determined from the
results of measurements of sound attenuation. The mechanism of adiabatic
renormalization of the amplitude of coherent tunneling is used for a
quantitative description of the peculiarities of sound absorption in the
vicinity of critical temperature.


title: Critical behavior of a cellular automaton highway traffic model

abstract:
  We derive the critical behavior of a CA traffic flow model using an order
parameter breaking the symmetry of the jam-free phase. Random braking appears
to be the symmetry-breaking field conjugate to the order parameter. For
$v_{\max}=2$, we determine the values of the critical exponents $\beta$,
$\gamma$ and $\delta$ using an order-3 cluster approximation and computer
simulations. These critical exponents satisfy a scaling relation, which can be
derived assuming that the order parameter is a generalized homogeneous function
of $|\rho-\rho_c|$ and p in the vicinity of the phase transition point.


title:
First-order phase transitions in non-equilibrium systems: New
  perspectives

abstract:
  First-order irreversible phase transitions (IPT's) between an active regime
and an absorbing state are studied in two models by means of both simulations
and mean-field stability analysis. Hysteresis around coexistence is the result
of the interplay of the length of the interface, its curvature, and a memory
effect related to the phase which is being removed. A controversy on the
occurrence of scale-invariance is clarified, conciliating the behavior of IPT's
with its reversible counterpart.


title: Diffusion-Limited Coalescence and Annihilation in Random Media

abstract:
  We study the kinetics of diffusion-limited coalescence, A+A->A, and
annihilation, A+A->0, in random media consisting of disconnected domains of
reaction. Examples include excitons fusion and annihilation in porous matrices
and along polymer chains. We begin with an exact analysis of A+A->A in a finite
segment. This result is applied to coalescence in a random distribution of
segment lengths, and the implications for coalescence and annihilation in
percolation clusters and other confined geometries are then derived by means of
scaling techniques.


title:
Spin configurations of carbon nanotube in a nonuniform external
  potential

abstract:
  We study, theoretically, the ground state spin of a carbon nanotube in the
presence of an external potential. We find that when the external potential is
applied to a part of the nanotube, its variation changes the single electron
spectrum significantly. This, in combination with Coulomb repulsion and the
symmetry properties of a finite length armchair nanotube induces spin flips in
the ground state when the external potential is varied. We discuss the possible
application of our theory to recent measurements of Coulomb blocked peaks and
their dependence on a weak magnetic field in armchair carbon nanotubes.


title:
Exactly solvable quantum spin ladders associated with the orthogonal and
  symplectic Lie algebras

abstract:
  We extend the results of spin ladder models associated with the Lie algebras
$su(2^n)$ to the case of the orthogonal and symplectic algebras $o(2^n),\
sp(2^n)$ where n is the number of legs for the system. Two classes of models
are found whose symmetry, either orthogonal or symplectic, has an explicit n
dependence. Integrability of these models is shown for an arbitrary coupling of
XX type rung interactions and applied magnetic field term.


title: Melting of Moving Vortex Lattices With Periodic Pinning

abstract:
  We study numerically the effects of temperature on moving vortex lattices
interacting with periodic pinning arrays. For low temperatures the vortex
lattice flows in channels, forming a hexatic structure with long range
transverse and longitudinal ordering. At higher temperatures, a transition to a
smectic state occurs where vortices wander between channels and longitudinal
order is lost while transverse order remains. At the highest temperatures the
vortex lattice melts into an isotropic liquid.


title:
One-dimensional tight-binding models with correlated diagonal and
  off-diagonal disorder

abstract:
  We study localization properties of electronic states in one-dimensional
lattices with nearest-neighbour interaction. Both the site energies and the
hopping amplitudes are supposed to be of arbitrary form. A few cases are
considered in details. We discuss first the case in which both the diagonal
potential and the fluctuating part of the hopping amplitudes are small. In this
case we derive a general analytical expression for the localization length,
which depends on the pair correlators of the diagonal and off-diagonal matrix
elements. The second case we investigate is that of strong uncorrelated
disorder, for which approximate analytical estimates are given and compared
with numerical data. Finally, we study the model with short-range correlations
which constitutes an extension with off-diagonal disorder of the random dimer
model.


title: Lebowitz Inequalities for Ashkin-Teller Systems

abstract:
  We consider the Ashkin-Teller model with negative four-spin coupling but
still in the region where the ground state is ferromagnetic. We establish the
standard Lebowitz inequality as well as the extension that is necessary to
prove a divergent susceptibility.


title: Cluster algorithms for general-S quantum spin systems

abstract:
  We present a general strategy to extend quantum cluster algorithms for S=1/2
spin systems, such as the loop algorithm, to systems with arbitrary size of
spins. In general, the partition function of a high-S spin system is
represented in terms of the path integral of a S=1/2 model with special
boundary conditions. We introduce additional graphs to be assigned to the
boundary part and give the labeling probability explicitly, which completes the
algorithm together with an existing S=1/2 cluster algorithm. As a demonstration
of the algorithm, we simulate the the integer-spin antiferromagnetic Heisenberg
chains. The magnitude of the first excitation gap is estimated as to be
0.41048(6), 0.08917(4), and 0.01002(3) for S=1, 2, and 3, respectively.


title: Renormalization-Group Approach to the Vulcanization Transition

abstract:
  The vulcanization transition - the crosslink-density-controlled equilibrium
phase transition from the liquid to the amorphous solid state - is explored
analytically from a renormalization group perspective. The analysis centers on
a minimal model that accounts for both the thermal motion of the constituents
and the quenched random constraints imposed on their motion by the crosslinks,
as well as particle-particle repulsion which suppresses density fluctuations. A
correlation function involving fluctuations of the amorphous solid order
parameter, the behavior of which signals the vulcanization transition, is
examined, its physical meaning is elucidated, and the associated susceptibility
is constructed and analyzed. A Ginzburg criterion for the width (in crosslink
density) of the critical region is derived and is found to be consistent with a
prediction due to de Gennes. Certain universal critical exponents
characterizing the vulcanization transition are computed, to lowest nontrivial
order, within the framework of an expansion around the upper critical dimension
of six. This expansion shows that the connection between vulcanization and
percolation extends beyond mean-field theory, at least to first order in the
departure from the upper critical dimension. The relationship between the
present approach to vulcanized matter and other approaches is explored in the
light of this connection. To conclude, some expectations for how the
vulcanization transition is realized in two dimensions, developed with H. E.
Castillo, are discussed.


title: Modulation structure of a frustrated spin ladder

abstract:
  We study a two-leg spin-1/2 ladder with isotropic exchanges and biquadratic
interactions in the basic plaquettes. It is shown that for the extremely
frustrated case, the system exhibits a self-organized phase separation. In some
parameter regions, the singlet rungs form a Wigner-like lattice in the
triplet-rung host. There are three types of elementary excitations in this
modulation phase, i.e., the spinons in a triplet domain, the broken singlet
rungs and the deformation of the Wigner-like lattice. The flux phase induced by
an external magnetic field in the rung-dimerized phase is also discussed.


title: Exact solution of a Kondo lattice model

abstract:
  An integrable Kondo lattice model, which describes a strongly correlated
electron host interacting with a spin-1/2 lattice, is proposed. It is found
that with the variations of the Kondo coupling J, the hole concentration n_h
and the magnetic field H, the system may fall into a variety of phases. The
phase boundaries of the ground state are determined exactly. The marginal
excitations and the quantum critical behavior at the phase boundaries are
discussed.


title: Quasi one dimensional $^4$He inside carbon nanotubes

abstract:
  We report results of diffusion Monte Carlo calculations for both $^4$He
absorbed in a narrow single walled carbon nanotube (R = 3.42 \AA) and strictly
one dimensional $^4$He. Inside the tube, the binding energy of liquid $^4$He is
approximately three times larger than on planar graphite. At low linear
densities, $^4$He in a nanotube is an experimental realization of a
one-dimensional quantum fluid. However, when the density increases the
structural and energetic properties of both systems differ. At high density, a
quasi-continuous liquid-solid phase transition is observed in both cases.


title: Solvable model for the standard folklore of the glassy state

abstract:
  A model system with fast and slow processes is introduced. After integrating
out the fast ones, the considered dynamics of the slow variables is exactly
solvable. In statics the system undergoes a Kauzmann transition to a glassy
state. The relaxation time obeys a generalized Vogel-Fulcher-Tammann-Hesse law.
The aging dynamics on the approach to and below the Kauzmann temperature is
analyzed; it has logarithmic behavior. The structure of the results could be
general, as they satisfy laws of thermodynamics far from equilibrium. The
original VFTH law is on the border-line between the regime where only the
effective temperature of the slow modes is needed, and the regime where also an
effective field occurs. The production rates of entropy and heat are
calculated.


title:
Effective mass of composite fermion: a phenomenological fit in with
  anomalous propagation of surface acoustic wave

abstract:
  We calculate the conductivity associated with the anomalous propagation of a
surface acoustic wave above a two-dimensional electron gas at $\nu=1/2$.
Murthy-Shankar's middle representation is adopted and a contribution to the
response functions beyond the random phase approximation has been taken into
account. We give a phenomenological fit for the effective mass of composite
fermion in with the experimental data of the anomalous propagation of surface
acoustic wave at $\nu=1/2$ and find the phenomenological value of the effective
mass is several times larger than the theoretical value
$m_{th}^*=6\epsilon/e^2l_{1/2}$ derived from the Hartree-Fock approximation. We
compare our phenomenologically fitting composite fermion effective mass with
those appeared in the measurements of the activation energy and the
Shubnikov-de Haas effect and find that our result is fairly reasonable.


title:
From Composite Fermions to Calogero-Sutherland Model: Edge of Fractional
  Quantum Hall Liquid and the Dimension Reduction

abstract:
  We derive a microscopic model describing the low-lying edge excitations in
the fractional quantum Hall liquid with $\nu=\frac{\nu^*} {\tilde\phi\nu^*+1}$.
For $\nu^*>0$, it is found that the composite fermion model reduces to an
SU$(\nu^*)$ Calogero-Sutherland model in a dimension reduction, whereas it is
not exact soluble for $\nu^*<0$. However, the ground states in both cases can
be found and the low-lying excitations can be shown the chiral Luttinger liquid
behaviors. On the other hand, we shows that the finite temperature behavior of
$G-T$ curve will deviate from the prediction of the chiral Luttinger liquid. We
also point out that the suppression of the `spin' degrees of freedom agrees
with very recent experiments by Chang et al. The two-boson model of Lee and Wen
is described microscopically.


title: Tunneling of a large spin via hyperfine interactions

abstract:
  We consider a large spin \bf S in the magnetic field parallel to the uniaxial
crystal field, interacting with N >> 1 nuclear spins \bf I_i via Hamiltonian
\cal H = -DS_z^2 - H_zS_z+ A{\bf S}\cdot \sum_{i=1}^N {\bf I}_i with A << D, at
temperature T. Tunneling splittings and the selection rules for the resonant
values of H_z are obtained perturbatively. The quantum coherence exists at T <<
ASI while at T >= ASI the coherence is destroyed and the relaxation of \bf S is
described by a stretched dependence which can be close to log t under certain
conditions. Relevance to Mn-12 acetate is discussed.


title: Dynamical Mean Field Theory and Electronic Structure Calculations

abstract:
  We formulate the dynamical mean field theory directly in the continuum. For a
given definition of the local Green's function, we show the existence of a
unique functional, whose stationary point gives the physical local Green's
function of the solid. We present the diagrammatic rules to calculate it
perturbatively in the interaction. Inspired by the success of dynamical mean
field calculations for model Hamiltonian systems, we present approximations to
the exact saddle point equations which may be used in the strong coupling
regime, by using mappings onto generalized quantum impurity models.


title:
Elastic Study of Antiferromagnetic Fluctuations in the Layered Organic
  Superconductors kappa-(BEDT-TTF)_2X

abstract:
  In an ultrasonic experiment, we have investigated the temperature profile of
the velocity of longitudinal elastic waves propagating along a direction
perpendicular to the layers in the organic superconductors kappa-(BEDT-TTF)_2X,
X = Cu(SCN)_2 and Cu[N(CN)_2]Br. Although a small decrease of the velocity is
observed at the superconducting transition, the most anomalous behavior is
obtained in the normal metallic state where an important softening is
identified around 40-50 K. In order to characterize the origin of this anomaly,
we have studied its behavior under the application of hydrostatic pressure. The
observed behavior is found to mimic those of the transport and magnetic
properties of these materials which have been attributed to the magnetic
fluctuations. Following the example of one-dimensional insulating systems where
coupling between longitudinal acoustic waves and magnetic fluctuations is known
to occur, our results suggest that the pseudo-gap regime of these
two-dimensional organic superconductors is dominated by a similar mechanism.


title:
Superconductivity in Ultrasmall Grains: Introduction to Richardson's
  Exact Solution

abstract:
  Studies of pairing correlations in ultrasmall metallic grains have commonly
been based on a simple reduced BCS-model describing the scattering of pairs of
electrons between discrete energy levels that come in time-reversed pairs. This
model has an exact solution, worked out by Richardson in the context of nuclear
physics in the 1960s. Here we give a tutorial introduction to his solution, and
use it to check the quality of various previous treatments of this model.

categories: cond-mat.str-el cond-mat.mes-hall math-ph math.MP nucl-th


title:
Size Segregation and Convection of Granular Mixtures Almost Completely
  Packed in the Rotating Thin Box

abstract:
  Size segregation of granular mixtures which are almost completely packed in a
rotating drum is discussed with an effective simulation and a brief analysis.
Instead of a 3D drum, we simulate 2D rotating thin box which is almost
completely packed with granular mixtures. The phase inversion of radially
segregated pattern which was found in a 3D experiment are qualitatively
reproduced with this simulation, and a brief analysis is followed. Moreover in
our simulation, a global convection appears after radial segregation pattern is
formed, and this convection induces axially segregated pattern.


title:
The ordered and orientationally disordered crystalline phases of the
  flexible C4F8 molecule

abstract:
  There is ample experimental evidence on the existence of several crystalline
phases of C4F8, although they still have been not clearly identified. In this
paper we perform a series of molecular dynamics (MD) simulations using a
partially flexible molecular model, which takes into account the mixing of the
low frequency intramolecular modes and lattice modes. The calculations are
carried on in the constant pressure- constant temperature ensemble and the
algorithm employed allows volume and symmetry changes of the MD sample as a
function of thermodynamic variables. Although several stable crystalline phases
are found, their number is still less than found by experiments.


title: High-quality continuous random networks

abstract:
  The continuous random network (CRN) model is an idealized model for perfectly
coordinated amorphous semiconductors. The quality of a CRN can be assessed in
terms of topological and configurational properties, including coordination,
bond-angle distributions and deformation energy. Using a variation on the
sillium approach proposed 14 years ago by Wooten, Winer and Weaire, we present
1000-atom and 4096-atom configurations with a degree of strain significantly
less than the best CRN available at the moment and, for the first time,
comparable to experimental results.


title:
Thermodynamics of supercooled liquids in the inherent structure
  formalism: a case study

abstract:
  In this article we review the thermodynamics of liquids in the framework of
the inherent structure formalism. We then present calculations of the
distribution of the basins in the potential energy of a binary Lennard-Jones
mixture as a function of temperature. The comparison between the numerical data
and the theoretical formalism allows us to evaluate the degeneracy of the
inherent structures in a bulk system and to estimate the energy of the lowest
energy disordered state (the Kauzmann energy). We find that, around the
mode-coupling temperature, the partition function of the liquid is approximated
well by the product of two loosely coupled partition functions, one depending
on the inherent structures quantities (depth of the basins and their
degeneracy) and one describing the free energy of the liquid constrained in one
typical basin.


title: A Monte Carlo Method for the Numerical Simulation of Tsallis Statistics

abstract:
  We present a new method devised to overcome the intrinsic difficulties
associated to the numerical simulations of the Tsallis statistics. We use a
standard Metropolis Monte Carlo algorithm at a fictitious temperature T',
combined with a numerical integration method for the calculation of the entropy
in order to evaluate the actual temperature T. We illustrate the method by
applying it to the 2d-Ising model using a standard reweighting technique.


title:
Matched asymptotic solutions for the steady banded flow of the diffusive
  Johnson-Segalman model in various geometries

abstract:
  We present analytic solutions for steady flow of the Johnson-Segalman (JS)
model with a diffusion term in various geometries and under controlled strain
rate conditions, using matched asymptotic expansions. The diffusion term
represents a singular perturbation that lifts the continuous degeneracy of
stable, banded, steady states present in the absence of diffusion. We show that
the stable steady flow solutions in Poiseuille and cylindrical Couette
geometries always have two bands. For Couette flow and small curvature, two
different banded solutions are possible, differing by the spatial sequence of
the two bands.


title: Incoherent Zener tunneling and its application to molecular magnets

abstract:
  We generalize the Landau-Zener theory of coherent tunneling transitions by
taking thermal relaxation into account. The evaluation of a new generalized
master equation containing a dynamic tunneling rate that includes the
interaction between the relevant system and its environment leads to an
incoherent Zener transition probability with an exponent that is twice as large
as the one of the coherent Zener probability in the limit T -> 0. We apply our
results to molecular clusters, in particular to recent measurements of the
tunneling transition of spins in Fe8 crystals performed by Wernsdorfer and
Sessoli [Science 284, 133 (1999)].


title: Entropy, Macroscopic Information, and Phase Transitions

abstract:
  The relationship between entropy and information is reviewed, taking into
account that information is stored in macroscopic degrees of freedom, such as
the order parameter in a system exhibiting spontaneous symmetry breaking. It is
shown that most problems of the relationship between entropy and information,
embodied in a variety of Maxwell demons, are also present in any symmetry
breaking transition.


title: Non-uniqueness of late-time scaling states in spinodal decomposition

abstract:
  In this letter we show that the late-time scaling state in spinodal
decomposition is not unique. We performed lattice Boltzmann simulations of the
phase-ordering of a 50%-50% binary mixture using as initial conditions for the
phase-ordering both a symmetric morphology that was created by symmetric
spinodal decomposition and a morphology of one phase dispersed in the other,
created by viscoelastic spinodal decomposition. We found two different growth
laws at late times, although both simulations differ only in the early time
dynamics. The new scaling state consists of dispersed droplets. The growth law
associated with this scaling state is consistent with a $L\sim t^{1/2}$ scaling
law.


title: Anomalous magnetic splitting of the Kondo resonance

abstract:
  The splitting of the Kondo resonance in the density of states of an Anderson
impurity in finite magnetic field is calculated from the exact Bethe-ansatz
solution. The result gives an estimate of the electron spectral function for
nonzero magnetic field and Kondo temperature, with consequences for transport
experiments on quantum dots in the Kondo regime. The strong correlations of the
Kondo ground state cause a significant low-temperature reduction of the peak
splitting. Explicit formulae are found for the shift and broadening of the
Kondo peaks. A likely cause of the problems of large-N approaches to spin-1/2
impurities at finite magnetic field is suggested.


title: Hydrodynamics of the Kuramoto-Sivashinsky Equation in Two Dimensions

abstract:
  The large scale properties of spatiotemporal chaos in the 2d
Kuramoto-Sivashinsky equation are studied using an explicit coarse graining
scheme. A set of intermediate equations are obtained. They describe
interactions between the small scale (e.g., cellular) structures and the
hydrodynamic degrees of freedom. Possible forms of the effective large scale
hydrodynamics are constructed and examined. Although a number of different
universality classes are allowed by symmetry, numerical results support the
simplest scenario, that being the KPZ universality class.

categories: cond-mat.soft chao-dyn cond-mat.dis-nn cond-mat.stat-mech nlin.CD nlin.PS patt-sol


title: Crossing Probabilities in Critical 2-D Percolation and Modular Forms

abstract:
  Crossing probabilities for critical 2-D percolation on large but finite
lattices have been derived via boundary conformal field theory. These
predictions agree very well with numerical results. However, their derivation
is heuristic and there is evidence of additional symmetries in the problem.
This contribution gives a preliminary examination some unusual modular behavior
of these quantities. In particular, the derivatives of the "horizontal" and
"horizontal-vertical" crossing probabilities transform as a vector modular
form, one component of which is an ordinary modular form and the other the
product of a modular form with the integral of a modular form. We include
consideration of the interplay between conformal and modular invariance that
arises.

categories: cond-mat.stat-mech hep-th math-ph math.MP math.NT


title:
Green's Function Monte Carlo for Lattice Fermions: Application to the
  t-J Model

abstract:
  We develop a general numerical method to study the zero temperature
properties of strongly correlated electron models on large lattices. The
technique, which resembles Green's Function Monte Carlo, projects the ground
state component from a trial wave function with no approximations. We use this
method to determine the phase diagram of the two-dimensional t-J model, using
the Maxwell construction to investigate electronic phase separation. The shell
effects of fermions on finite-sized periodic lattices are minimized by keeping
the number of electrons fixed at a closed-shell configuration and varying the
size of the lattice. Results obtained for various electron numbers
corresponding to different closed-shells indicate that the finite-size effects
in our calculation are small. For any value of interaction strength, we find
that there is always a value of the electron density above which the system can
lower its energy by forming a two-component phase separated state. Our results
are compared with other calculations on the t-J model. We find that the most
accurate results are consistent with phase separation at all interaction
strengths.


title:
New representations of the Hecke algebra and algebraic Bethe Ansatz for
  an integrable generalized spin ladder

abstract:
  This paper has been withdrawn by the authors, due an error in Bethe Ansatz
equations (16).


title:
Sleep-Wake Differences in Scaling Behavior of the Human Heartbeat:
  Analysis of Terrestrial and Long-Term Space Flight Data

abstract:
  We compare scaling properties of the cardiac dynamics during sleep and wake
periods for healthy individuals, cosmonauts during orbital flight, and subjects
with severe heart disease. For all three groups, we find a greater degree of
anticorrelation in the heartbeat fluctuations during sleep compared to wake
periods. The sleep-wake difference in the scaling exponents for the three
groups is comparable to the difference between healthy and diseased
individuals. The observed scaling differences are not accounted for simply by
different levels of activity, but appear related to intrinsic changes in the
neuroautonomic control of the heartbeat.


title: Phase diagram of the su(8) quantum spin tube

abstract:
  We calculate the phase diagram of an integrable anisotropic 3-leg quantum
spin tube connected to the su(8) algebra. We find several quantum phase
transitions for antiferromagnetic rung couplings. Their locations are
calculated exactly from the Bethe Ansatz solution and we discuss the nature of
each of the different phases.


title: Hierarchical model for the scale-dependent velocity of seismic waves

abstract:
  Elastic waves of short wavelength propagating through the upper layer of the
Earth appear to move faster at large separations of source and receiver than at
short separations. This scale dependent velocity is a manifestation of Fermat's
principle of least time in a medium with random velocity fluctuations. Existing
perturbation theories predict a linear increase of the velocity shift with
increasing separation, and cannot describe the saturation of the velocity shift
at large separations that is seen in computer simulations. Here we show that
this long-standing problem in seismology can be solved using a model developed
originally in the context of polymer physics. We find that the saturation
velocity scales with the four-third power of the root-mean-square amplitude of
the velocity fluctuations, in good agreement with the computer simulations.


title: Charge Fluctuations in the Edge States of N-S hybrid Nano-Structures

abstract:
  In this work we show how to calculate the equilibrium and non-equilibrium
charge fluctuations in a gated normal mesoscopic conductor which is attached to
one normal lead and one superconducting lead. We then consider an example where
the structure is placed in a high magnetic field, such that the transport is
dominated by edge states. We calculate the equilibrium and non-equilibrium
charge fluctuations in the gate, for a single edge state, comparing our results
to those for the same system, but with two normal leads. We then consider the
specific example of a quantum point contact and calculate the charge
fluctuations in the gate for more than one edge state.


title: A simple system with two temperatures

abstract:
  We study the stationary nonequilibrium regime which settles in when two
single-spin paramagnets each in contact with its own thermal bath are coupled.
The response vs. correlation plot exhibits some features of aging systems, in
particular the existence, in some regimes, of effective temperatures.


title: Multiplicity of species in some replicative systems

abstract:
  In an attempt to explain the uniqueness of the coding mechanism of living
cells as contrasted with multi-species structure of ecosystems we examine two
models of individuals with some replicative properties. In the first model the
system generically remains in a multi-species state. Even though for some of
these species the replicative probability is very high, they are unable to
invade the system. In the second model, in which the death rate depends on the
type of the species, the system relatively quickly reaches a single-species
state and fluctuations might at most bring it to yet another single-species
state.


title: Polarization induced by charged particles in real solids

abstract:
  We report a first-principles description of the induced wake potential and
density in real solids. The linear-response formalism is used to obtain the
potential and density induced by an external charge penetrating through an
inhomogeneous periodic system. The linear dynamical response of the system is
evaluated in the random-phase approximation, by including the full band
structure of the solid. The impact of the periodic crystalline potential is
analyzed, and variations of the wake along different channels in Al and Si are
investigated.


title: Zero-temperature phase diagram of binary boson-fermion mixtures

abstract:
  We calculate the phase diagram for dilute mixtures of bosons and fermions at
zero temperature. The linear stability conditions are derived and related to
the effective boson-induced interaction between the fermions. We show that in
equilibrium there are three possibilities: a) a single uniform phase, b) a
purely fermionic phase coexisting with a purely bosonic one and c) a purely
fermionic phase coexisting with a mixed phase.


title:
Wall induced density profiles and density correlations in confined
  Takahashi lattice gases

abstract:
  We propose a general formalism to study the static properties of a system
composed of particles with nearest neighbor interactions that are located on
the sites of a one-dimensional lattice confined by walls (``confined Takahashi
lattice gas''). Linear recursion relations for generalized partition functions
are derived, from which thermodynamic quantities, as well as density
distributions and correlation functions of arbitrary order can be determined in
the presence of an external potential. Explicit results for density profiles
and pair correlations near a wall are presented for various situations. As a
special case of the Takahashi model we consider in particular the hard rod
lattice gas, for which a system of nonlinear coupled difference equations for
the occupation probabilities has been presented previously by Robledo and
Varea. A solution of these equations is given in terms of the solution of a
system of independent linear equations. Moreover, for zero external potential
in the hard rod system we specify various central regions between the confining
walls, where the occupation probabilities are constant and the correlation
functions are translationally invariant in the canonical ensemble. In the grand
canonical ensemble such regions do not exist.


title: Vortex in Chiral Superconducting State

abstract:
  We have investigated the vortex in chiral superconductors, especially in
p-wave case. In chiral superconductors the Cooper pair has orbital angular
momentum hence U(1), parity (P) and time reversal symmetry (T) are broken
simultaneously. We have found that the vortex has fractional charge and
fractional angular momentum which comes from P- and T-violation. The
fractionalization of the angular momentum suggests that the vortex could be
anyon which obeys the fractional statistics. We have also pointed out that the
electric field is induced near the vortex core and non-trivial electromagnetic
phenomena are expected to occur.


title: Correlated correlation functions in random-bond ferromagnets

abstract:
  The two-dimensional random-bond Q-state Potts model is studied for Q near 2
via the perturbative renormalisation group to one loop. It is shown that weak
disorder induces cross-correlations between the quenched-averages of moments of
the two-point spin/spin and energy/energy correlation functions, which should
be observable numerically in specific linear combinations of various quenched
correlation functions. The random-bond Ising model in (2+epsilon) dimensions is
similarly treated. As a byproduct, a simple method for deriving the scaling
dimensions of all moments of the local energy operator is presented.


title:
Phonon exchange in dilute Fermi-Bose mixtures: tailoring the Fermi-Fermi
  interaction

abstract:
  We consider a mixture of a single-component Bose gas and a two-component
Fermi gas at temperatures where the Bose gas is almost fully condensed. In such
a mixture, two fermionic atoms can interact with each other by exchanging a
phonon that propagates through the Bose condensate. We calculate the
interaction potential due to this mechanism and determine the effective s-wave
scattering length for two fermions that interact, both directly by the
interatomic potentials, as well as by the above mentioned exchange mechanism.
We find that the effective scattering length is quite sensitive to changes in
the condensate density and becomes strongly energy dependent. In addition, we
consider the mechanical stability of these mixtures and also calculate the
dispersion and the damping of the various collisionless collective modes of the
gas.


title:
Cosmology in a Test Tube: Theory of Domain Walls Formation in Binary
  Fluids

abstract:
  Formation of domain walls during a rapid phase transition in a quasi one
dimensional Cahn-Hiliard equation describing binary fluids in a thin tube is
studied. Density of kinks scales like a sixth root of quench rate for equal
concentrations and like a square root of quench rate for unequal concentrations
of fluids. For a slow inhomogeneous transition the density is linear in
velocity of temperature front. This paper is first theoretical study of
topological defects formation in a system with conserved order parameter.


title: A scenario for the dynamics in the small intropy production limit

abstract:
  We present a scenario for the nonequilibrium dynamics in the limit of small
entropy production. We discuss (i) the appearence of different time-scales,
(ii) the modification of the fluctuation-dissipation theorem and its relation
to effective temperatures and partial equilibrations and (iii) the validity of
Onsager reciprocity relations. We distinguish these properties by their
reaction to infinitesimal perturbations. We recall that one can easily change
the time dependence of observables by applying an infinitesimal force while
time-reparametrization invariant features remain unchanged under the same
perturbations. With the aim of better understanding these properties, we
consider the effect of several baths with different temperatures and
time-scales on the dynamics. This is done in two ways: numerically, by using a
especially developed Monte Carlo algorithm that mimics the coupling to multiple
baths; analytically, by computing the time-dependent probability density of
simple systems in contact with multiple baths. We finally argue that these
features are related to supersymmetry, the reparametrization invariance of the
slow dynamics and its spontaneous breaking. This scenario is consistent within
any perturbative scheme. A brief version of this article appeared in Physica
A263, 242 (1999).


title: Edge magnetoplasmons in periodically modulated structures

abstract:
  We present a microscopic treatment of edge magnetoplasmons (EMP's) within the
random-phase approximation for strong magnetic fields, low temperatures, and
filling factor $\nu =1(2)$, when a weak short-period superlattice potential is
imposed along the Hall bar. The modulation potential modifies both the spatial
structure and the dispersion relation of the fundamental EMP and leads to the
appearance of a novel gapless mode of the fundamental EMP. For sufficiently
weak modulation strengths the phase velocity of this novel mode is almost the
same as the group velocity of the edge states but it should be quite smaller
for stronger modulation. We discuss in detail the spatial structure of the
charge density of the renormalized and the novel fundamental EMP's.


title:
Polaron states of electrons over the anisotropic surface of liquid
  helium

abstract:
  The energetics and transport properties of the polaron in the anisotropic
surface over liquid helium are investigated. The localization radii and the
energy of the ground and excited states are calculated using the variational
method within the hydrodynamic model of the polaron. In particular, we have
considered maximal anisotropy which corresponds to the system of electrons in
quasi-one-dimensional channels over liquid helium. The polaron binding energy
is found and the temperature for the polaron formation is estimated below 0.1
K. Solving the hydrodynamic equations for fluid velocities, the polaron
mobilities along and across the channel are determined. The possibility of
experimental observation of polarons by measuring the frequency of
spectroscopic transitions as well the mobility as functions of the holding
electric field is addressed.


title:
Atomic Bose-Einstein Condensation with Three-Body Interactions and
  Collective Excitations

abstract:
  The stability of a Bose-Einstein condensed state of trapped ultra-cold atoms
is investigated under the assumption of an attractive two-body and a repulsive
three-body interaction. The Ginzburg-Pitaevskii-Gross (GPG) nonlinear
Schr\"odinger equation is extended to include an effective potential dependent
on the square of the density and solved numerically for the s-wave. The lowest
frequency of the collective mode is determined and its dependences on the
number of atoms and on the strength of the three-body force are studied. We
show that the addition of three-body dynamics can allow the number of condensed
atoms to increase considerably, even when the strength of the three-body force
is very small compared with the strength of the two-body force. We also observe
a first-order liquid-gas phase transition for the condensed state up to a
critical strength of the effective three-body force.


title: Re-examination of seven-dimensional site percolation thresholds

abstract:
  Monte Carlo simulations alone could not clarify the corrections to scaling
for the size-dependent p_c(L) above the upper critical dimension. Including the
previous series estimate for the bulk threshold $p_c(\infty)$ gives preference
for the complicated corrections predicted by renormalization group and against
the simple 1/L extrapolation. Additional Monte-Carlo simulations using the
Leath method corroborate the series result for p_c.


title: Magnetic Order in the Double Exchange Model in Infinite Dimensions

abstract:
  We studied magnetic properties of the double exchange (DE) model with S=1/2
localized spins at T=0, using exact diagonalization in the framework of the
dynamical mean field theory. Obtained phase diagram contains ferromagnetic,
antiferromagnetic and paramagnetic phases. Comparing the phase diagram with
that of the DE model with classical localized spins, we found that the quantum
fluctuations of localized spins partly destabilize the ferromagnetism and
expand the paramagnetic phase region. We found that phase separations occur
between the antiferromagnetic and paramagnetic phases as well as the
paramagnetic and ferromagnetic ones.


title: Non-Fermi liquid behavior in U and Ce intermetallics

abstract:
  In this paper we review the current experimental and theoretical situation of
the description of non-Fermi liquid behavior (NFL) in U and Ce intermetallics.
We focus on the magnetic and thermodynamic properties. We also discuss a recent
theoretical interpretation of this behavior in terms of Griffiths-McCoy
singularities close to the magnetic quantum critical point (QCP). We show how
an effective Hamiltonian which contains both the RKKY coupling and the Kondo
interaction can be written after high energy degrees of freedom away from the
Fermi surface are traced out. We argue that dissipation due to particle-hole
excitations close to the Fermi surface is a relevant perturbation at low
temperatures and we estimate the crossover temperature T^* above which power
law behavior in specific heat and magnetic response occurs ($C_V/T \sim \chi(T)
\propto T^{-1+\lambda}$ with $\lambda<1$). Below T^* a new regime dominated by
dissipation is found and deviations from power law behavior are expected.


title: Electrical Resistivity of a Thin Metallic Film

abstract:
  The electrical resistivity of a pure sample of a thin metallic film is found
to depend on the boundary conditions. This conclusion is supported by a
free-electron model calculation and confirmed by an ab initio relativistic
Korringa-Kohn-Rostoker computation. The low-temperature resistivity is found to
be zero for a free-standing film (reflecting boundary conditions) but nonzero
when the film is sandwiched between two semi-infinite samples of the same
material (outgoing boundary conditions). In the latter case, this resistivity
scales inversely with the number of monolayers and is due to the background
diffusive scattering by a finite lattice.


title:
ESR investigation on the Breather mode and the Spinon-Breather dynamical
  crossover in Cu Benzoate

abstract:
  A new elementary-excitation, the so called "breather excitation", is observed
directly by millimeter-submillimeter wave electron spin resonance (ESR) in the
Heisenberg quantum spin-chain Cu benzoate, in which a field-induced gap is
found recently by specific heat and neutron scattering measurements. Distinct
anomalies were found in line width and in resonance field around the "dynamical
crossover" regime between the gap-less spinon-regime and the gapped
breather-regime. When the temperature becomes sufficiently lower than the
energy gap, a new ESR-line with very narrow line-width is found, which is the
manifestation of the breather excitation. The non-linear field dependence of
the resonance field agrees well with the theoretical formula of the first
breather-excitation proposed by Oshikawa and Affleck. The present work
establishes experimentally for the first time that a sine-Gordon model is
applicable to explain spin dynamics in a S=1/2 Heisenberg spin chain subjected
to staggered field even in high fields.


title: Fermionic field theory for directed percolation in (1+1) dimensions

abstract:
  We formulate directed percolation in (1+1) dimensions in the language of a
reaction-diffusion process with exclusion taking place in one space dimension.
We map the master equation that describes the dynamics of the system onto a
quantum spin chain problem. From there we build an interacting fermionic field
theory of a new type. We study the resulting theory using renormalization group
techniques. This yields numerical estimates for the critical exponents and
provides a new alternative analytic systematic procedure to study
low-dimensional directed percolation.


title: Solution of a two leg spin ladder system

abstract:
  A new model for a spin 1/2 ladder system with two legs is introduced. It is
demonstrated that this model is solvable via the Bethe ansatz method for
arbitrary values of the rung coupling J. This is achieved by a suitable mapping
from the Hubbard model with appropriate twisted boundary conditions. We
determine that a phase transition between gapped and gapless spin excitations
occurs at the critical value J_c=1/2 of the rung coupling.


title: X-Ray Diffraction from Pinned Charge Density Waves

abstract:
  We present an x-ray study of doped charge density waves systems. When a
2k_f-charge density wave is strongly pinned to impurities, an interference
effect gives rise to an asymmetry between the intensities of the +2k_f and
-2k_f satellite reflections. Moreover, profile asymmetry of the satellite
reflections indicates the existence of Friedel oscillations (FOs) around the
defects. We have studied these effects in V- and W-doped blue bronzes. A
syncrotron radiation study of the V-doped blue bronze clearly reveals the
presence of FO around the V atoms.


title:
Phase Diagrams of Mixed Spin Chains with Period 4 by the Nonlinear
  $\sigma$ Model

abstract:
  We study mixed quantum spin chains consisting of two kinds of spins with
magnitudes, s_a and s_b. The spins are arrayed as s_a-s_a-s_b-s_b in a unit
cell and the exchange couplings are accordingly periodic with period 4. The
spin Hamiltonian is mapped onto a nonlinear $\sigma$ model based on the general
formula for periodic inhomogeneous spin chains. The gapless condition given by
the nonlinear $\sigma$ model determines boundaries between disordered phases in
the space of the exchange parameters. The phase diagram has a rich phase
structure characterized by the values of s_a and s_b. We explain all phases in
the singlet-cluster-solid picture which is an extension of the
valence-bond-solid picture.


title:
Duality picture between antiferromagnetism and d-wave superconductivity
  in t-J model at two dimensions

abstract:
  We show in this paper an interesting relation between elementary and
topological excitations in the antiferromagnetic and d-wave superconducting
phases of the t-J model at two dimenions. The topological spin and charge
excitations in one phase have the same dynamics as elementary excitations in
the other phase, except the appearance of energy gaps. Moreover, the transition
from one phase to another can be described as a quantum disordering transition
associated with the topological excitations. Based on the above picture, a
plausible phase diagram of t-J model is constructed.


title:
Nonlinear conduction of sliding electronic crystals: Charge and Spin
  Density Waves

abstract:
  A model of local metastable states due to the pinning induces plastic
deformations allows to describe the nonlinear I-V curves in sliding density
waves -DW. With increasing the DW velocity v, the metastable states of
decreasing lifetimes ~1/v are accessed. The characteristic second threshold
field is reached when configurations of shortest life time are accessed by the
fast moving DW. Thus the DW works as a kind of a ``linear accelerator'' testing
virtual states.


title: Opposite Thermodynamic Arrows of Time

abstract:
  A model in which two weakly coupled systems maintain opposite running
thermodynamic arrows of time is exhibited. Each experiences its own retarded
electromagnetic interaction and can be seen by the other. The possibility of
opposite-arrow systems at stellar distances is explored and a relation to dark
matter suggested.


title: Internal Friction of Amorphous Silicon in a Magnetic Field

abstract:
  The internal friction of e-beam amorphous silicon was measured in a magnetic
field between 0 and 6 T, from 1.5-20 K, and was found to be independent of the
field to better than 8%. It is concluded that the low energy excitations
observed in this experiment are predominantly atomic in nature.


title: Electron transport through a mesoscopic metal-CDW-metal junction

abstract:
  In this work we study the transport properties of a finite Peierls-Fr\"ohlich
dielectric with a charge density wave of the commensurate type. We show that at
low temperatures this problem can be mapped onto a problem of fractional charge
transport through a finite-length correlated dielectric, recently studied by
Ponomarenko and Nagaosa [Phys. Rev. Lett {\bf 81}, 2304 (1998)]. The
temperature dependence of conductance of the charge density wave junction is
presented for a wide range of temperatures.


title:
Stokes formula and density perturbances for driven tracer diffusion in
  an adsorbed monolayer

abstract:
  We study the intrinsic friction of monolayers adsorbed on solid surfaces from
a gas phase or vapor. Within the framework of the Langmuir model of delocalized
adsorption, we calculate the resistance offered by the mobile adsorbate's
particles to some impure tracer molecule, whose diffusive random motion is
biased by a constant external force. We find that for sufficiently small
driving forces the force exerted on the tracer shows viscous-like behavior. We
derive then the analog of the Stokes formula for two-dimensional adsorbates,
calculate the corresponding friction coefficient and determine the stationary
particle distribution in the monolayer as seen from the driven impurity.


title:
Instability due to long range Coulomb interaction in a liquid of
  polarizable particles (polarons, etc.)

abstract:
  The interaction Hamiltonian for a system of polarons a la Feynman in the
presence of long range Coulomb interaction is derived and the dielectric
function is computed in mean field. For large enough concentration a liquid of
such particles becomes unstable. The onset of the instability is signaled by
the softening of a collective optical mode in which all electrons oscillate in
phase in their respective self-trapping potential. We associate the instability
with a metallization of the system. Optical experiments in slightly doped
cuprates and doped nickelates are analyzed within this theory.
  We discuss why doped cuprates matallize whereas nickelates do not.


title:
Feedback Effect on Landau-Zener-Stueckelberg Transitions in Magnetic
  Systems

abstract:
  We examine the effect of the dynamics of the internal magnetic field on the
staircase magnetization curves observed in large-spin molecular magnets. We
show that the size of the magnetization steps depends sensitively on the
intermolecular interactions, even if these are very small compared to the
intra-molecular couplings.


title: Thermodynamics of Self-Gravitating Systems with Softened Potentials

abstract:
  The microcanonical statistical mechanics of a set of self-gravitating
particles is analyzed in mean-field approach. In order to deal with an upper
bounded entropy functional, a softened gravitational potential is used. The
softening is achieved by truncating to N terms an expansion of the Newtonian
potential in spherical Bessel functions. The order N is related to the
softening at short distances. This regularization has the remarkable property
that it allows for an exact solution of the mean field equation. It is found
that for N not too large the absolute maximum of the entropy coincides to high
accuracy with the solution of the Lane-Emden equation, which determines the
mean field mass distribution for the Newtonian potential for energies larger
than $E_c\approx -0.335 G M^2/R$. Below this energy a collapsing phase
transition, with negative specific heat, takes place. The dependence of this
result on the regularizing parameter N is discussed.


title: Dispersion of Ordered Stripe Phases in the Cuprates

abstract:
  A phase separation model is presented for the stripe phase of the cuprates,
which allows the doping dependence of the photoemission spectra to be
calculated. The idealized limit of a well-ordered array of magnetic and charged
stripes is analyzed, including effects of long-range Coulomb repulsion.
Remarkably, down to the limit of two-cell wide stripes, the dispersion can be
interpreted as essentially a superposition of the two end-phase dispersions,
with superposed minigaps associated with the lattice periodicity. The largest
minigap falls near the Fermi level; it can be enhanced by proximity to a (bulk)
Van Hove singularity. The calculated spectra are dominated by two features --
this charge stripe minigap plus the magnetic stripe Hubbard gap. There is a
strong correlation between these two features and the experimental
photoemission results of a two-peak dispersion in La$_{2-x}$Sr$_x$CuO$_4$, and
the peak-dip-hump spectra in Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$. The
differences are suggestive of the role of increasing stripe fluctuations. The
1/8 anomaly is associated with a quantum critical point, here expressed as a
percolation-like crossover. A model is proposed for the limiting minority
magnetic phase as an isolated two-leg ladder.


title: Stability and dynamics of free magnetic polarons

abstract:
  The stability and dynamics of a free magnetic polaron are studied by Monte
Carlo simulation of a classical two-dimensional Heisenberg model coupled to a
single electron. We compare our results to the earlier mean-field analysis of
the stability of the polaron, finding qualitative similarity but quantitative
differences. The dynamical simulations give estimates of the temperature
dependence of the polaron diffusion, as well as a crossover to a tunnelling
regime.


title: Why Effective Medium Theory Fails in Granular Materials

abstract:
  Experimentally it is known that the bulk modulus, K, and shear modulus, \mu,
of a granular assembly of elastic spheres increase with pressure, p, faster
than the p^1/3 law predicted by effective medium theory (EMT) based on
Hertz-Mindlin contact forces. To understand the origin of these discrepancies,
we perform numerical simulations of granular aggregates under compression. We
show that EMT can describe the moduli pressure dependence if one includes the
increasing number of grain-grain contacts with p. Most important, the affine
assumption (which underlies EMT), is found to be valid for K(p) but breakdown
seriously for \mu(p). This explains why the experimental and numerical values
of \mu(p) are much smaller than the EMT predictions.


title: Inertial Effects on Fluid Flow through Disordered Media

abstract:
  We investigate the origin of the deviations from the classical Darcy law by
numerical simulation of the Navier-Stokes equations in two-dimensional
disordered porous media. We apply the Forchheimer equation as a
phenomenological model to correlate the variations of the friction factor for
different porosities and flow conditions. At sufficiently high Reynolds
numbers, when inertia becomes relevant, we observe a transition from linear to
non-linear behavior which is typical of experiments. We find that such a
transition can be understood and statistically characterized in terms of the
spatial distribution of kinetic energy in the system.


title: Self-localization of directed polymers and oppressive population control

abstract:
  We construct a phenomenological theory of self-localization of directed
polymers in d+1 dimensions. In d=1 we show that the polymer is always
self-localized, whereas in d=2 there is a phase transition between localized
and free states. We also map this system to a model of population dynamics with
fixed total population. Our previous results translate to static and expanding
population clusters, depending on the birth and death rates. A novel
``pseudo-travelling wave'' is observed in some sectors of parameter space.


title:
Rotation in an asymmetric multidimensional periodic potential due to
  colored noise

abstract:
  We analyze the motion of an overdamped classical particle in a
multidimensional periodic potential, driven by a weak external noise. We
demonstrate that in steady-state, the presence of temporal correlations in the
noise and spatial asymmetry within a period of the potential could lead to
particle rotation. The rotation is a direct consequence of a change in sign of
the noise-induced drift motion in each dimension. By choosing different
potentials, we can generate a variety of flow patterns from laminar drifts to
rotations.


title:
The Mott transition in V_2 O_3 and Ni Se_x S_{2-x}: insights from
  dynamical mean field theory

abstract:
  We discuss some aspects of the pressure (or interaction) driven Mott
transition, in three dimensional transition metal oxides by means of dynami cal
mean field theory. We isolate the universal properties of the transition from
the aspects which depend more on the detailed chemistry of the compounds. In
this light we can understand the main differences and the remarkable
similarities between these systems. Both theory and experiment converge on the
transfer of spectral weight from low energies to high energies as the universal
mechanism underlying the Mott transition, and we comment on the possible
relevance of these ideas to other metal to non metal transitions.


title:
Two-Loop Renormalization of the Quasiparticle Weight in Two-Dimensional
  Electron Systems

abstract:
  We apply the renormalization-group (RG) approach to two model systems where
the two-dimensional Fermi surface has portions which give rise to the
logarithmically singular two-loop self-energy process.


title: c-Axis Superfluid Response and Pseudogap in High-Tc Superconductors

abstract:
  To gain insight into the out-of-plane electrodynamics of high-$T_c$
superconduct ors we have measured the absolute values and temperature
dependence of the c-a xis magnetic penetration depth $\lambda_c(T)$ for two
typical single layer high -$T_c$ cuprates, La$_{2-x}$Sr$_x$CuO$_4$ and
HgBa$_2$CuO$_{4+x}$ as a function o f doping. A distinct change in the
behaviour of $\lambda_c$ is observed near 0. 20 holes/Cu, which is related to
the opening of the normal state pseudogap. The variation of $\lambda_c$ with
doping is qualitatively similar to that of the in -plane component, $\lambda
_{ab}$, which suggests that the c-axis superfluid r esponse is mainly governed
by the superconducting condensation energy. The stron g doping dependence of
$\lambda_c(0)$ for p<0.20 provides an explanation for the discrepancies in the
literature.


title:
Local density of states around a magnetic impurity in high-Tc
  superconductors based on the t-J model

abstract:
  The local density of states (LDOS) around a magnetic impurity in high-Tc
superconductors is studied using the two-dimensional t-J model with a realistic
band structure. The order parameters are determined in a self-consistent way
within the Gutzwiller approximation and the Bogoliubov-de Gennes theory. In
sharp contrast with the nonmagnetic impurity case, the LDOS near the magnetic
impurity shows two resonance peaks reflecting the presence of spin-dependent
resonance states. It is also shown that these resonance states are
approximately localized around the impurity. The present results have an large
implication on the scanning tunneling spectroscopy observation of
Bi_{2}Sr_{2}Ca(Cu_{1-x}Ni[Zn]_{x})_{2}O_{8+delta}.


title:
Correlated hopping in the Falicov-Kimball model: A large-dimensions
  study

abstract:
  The Falicov-Kimball model with a correlated-hopping interaction is solved
using an extended dynamical mean-field theory that becomes exact in the limit
of large dimensions. The effect of correlated hopping is to introduce nonlocal
self-energy components that retain full dynamics as D goes to infinity, thus
introducing an explicit k-dependence to the single-particle self-energy. An
explicit solution for the homogeneous phase at D = 2 reveals significant
nonlocal dynamical contributions in the physically relevant regime of a
moderately large correlated-hopping amplitude, indicating that important
nonlocal correlations are omitted in Hubbard-like models upon neglecting the
correlated-hopping interaction.


title: Spin-Peierls transition in an anisotropic two-dimensional XY model

abstract:
  The two-dimensional Jordan-Wigner transformation is used to investigate the
zero temperature spin-Peierls transition for an anisotropic two-dimensional XY
model in adiabatic limit. The phase diagram between the dimerized (D) state and
uniform (U) state is shown in the parameter space of dimensionless interchain
coupling $h$ $(=J_{\perp}/J)$ and spin-lattice coupling $\eta$. It is found
that the spin-lattice coupling $\eta$ must exceed some critical value $\eta_c$
in order to reach the D phase for any finite $h$. The dependence of $\eta_c$ on
$h$ is given by $-1/\ln h$ for $h\to 0$ and the transition between U and D
phase is of first-order for at least $h>10^{-3}$.


title: Zero-Temperature Critical Phenomena in Two-Dimensional Spin Glasses

abstract:
  Recent developments in study of two-dimensional spin glass models are
reviewed in light of fractal nature of droplets at zero-temperature. Also
presented are some new results including a new estimate of the stiffness
exponent using a boundary condition different from conventional ones.


title:
Thermodynamics and Gravitation: From Glasses to Black Holes and Globular
  Star Clusters

abstract:
  The topic of this conference is ``The Chaotic Universe''. One of the main
achievements of last century has been to relate chaos in fluids to their
thermodynamics. It is our purpose to make connection between chaos in
gravitation and standard thermodynamics. Though there have been many previous
steps and attempts, so far no convincing conclusion has been reached.
  After explaining how the approach works for glasses, we shall discuss the
thermodynamics of two specific systems: black holes and globular star clusters.
In both cases we point out that the dynamics satisfies the first and second law
of thermodynamics, though negative specific heats occur.


title:
Orbitally Driven Spin Pairing in the 3D Non-Magnetic Mott Insulator
  BaVS3: Evidence from Single Crystal Studies

abstract:
  Static electrical and magnetic properties of single crystal BaVS_3 were
measured over the structural (T_S=240K), metal-insulator (T_MI=69K), and
suspected orbital ordering (T_X=30K) transitions. The resistivity is almost
isotropic both in the metallic and insulating states. An anomaly in the
magnetic anisotropy at T_X signals a phase transition to an ordered low-T
state. The results are interpreted in terms of orbital ordering and spin
pairing within the lowest crystal field quasi-doublet. The disordered insulator
at T_X<T<T_MI is described as a classical liquid of non-magnetic pairs.


title: Isotope effect in the presence of a pseudogap

abstract:
  We investigate the question whether the unusual doping dependence of the
isotope exponent observed in underdoped high-Tc superconductors might be
related to another unusual phenomenon observed in these systems: the pseudogap
phenomenon. Within different approximations we study the influence of a
phenomenological pseudogap on the isotope exponent and find that it generally
strongly increases the isotope exponent, in qualitative agreement with
experiments on underdoped high-Tc compounds. This result is stable against
strong-coupling self-energy corrections and also holds for recently proposed
spinfluctuation exchange models, if a weak additional electron-phonon coupling
is considered.


title:
Concentration Profiles and Reaction Fronts in A + B -> C Type Processes:
  Effect of Background Ions

abstract:
  Diffusion and reaction of initially separated ions A- and B+ in the presence
of counter ions A'+ and B'- is studied. The dynamics is described in terms of
reaction-diffusion equations obeying local electroneutrality, and the
time-evolution of ion-concentrations is determined. We find that, in the
absence of reactions, unequal mobility of ions generate nontrivial features in
the macroscopically observable concentration profiles. Switching on the
reaction (A-) + (B+) -> C leads to the formation of a localized, diffusive
reaction front and one finds that the properties of the front (e.g. effective
diffusion constant) are affected by the background ions. The consequences of
this effect on the formation of Liesegang patterns is discussed.


title:
Hopping Transport in the Presence of Site Energy Disorder: Temperature
  and Concentration Scaling of Conductivity Spectra

abstract:
  Recent measurements on ion conducting glasses have revealed that conductivity
spectra for various temperatures and ionic concentrations can be superimposed
onto a common master curve by an appropriate rescaling of the conductivity and
frequency. In order to understand the origin of the observed scaling behavior,
we investigate by Monte Carlo simulations the diffusion of particles in a
lattice with site energy disorder for a wide range of both temperatures and
concentrations. While the model can account for the changes in ionic activation
energies upon changing the concentration, it in general yields conductivity
spectra that exhibit no scaling behavior. However, for typical concentrations
and sufficiently low temperatures, a fairly good data collapse is obtained
analogous to that found in experiment.


title: Dipolar interactions induced order in assemblies of magnetic particles

abstract:
  We discuss the appareance of ordered structures in assemblies of magnetic
particles. The phenomenon occurs when dipolar interactions and the thermal
motion of the particles compete, and is mediated by screening and excluded
volume effects. It is observed irrespective of the dimensionality of the system
and the resulting structures, which may be regular or fractal, indicate that
new ordered phases may emerge in these system when dipolar interactions play a
significant role.


title: Far-infrared spectroscopy of nanoscopic InAs rings

abstract:
  We have employed time-dependent local-spin density theory to analyze the
far-infrared transmission spectrum of InAs self-assembled nano-rings recently
reported [A. Lorke et al, cond-mat/9908263 (1999)]. The overall agreement
between theory and experiment is good, which on the one hand confirms that the
experimental peaks indeed reflect the ring-like structure of the sample, and on
the other hand, asseses the suitability of the theoretical method to describe
such small nanostructures. The addition energies of one- and two-electron rings
are also reported and compared with the corresponding capacitance spectra.


title:
Theory of internal transitions of charged excitons in quantum wells in
  magnetic fields

abstract:
  For charged semiconductor complexes in magnetic fields B, we discuss an exact
classification of states, which is based on magnetic translations. In this
scheme, in addition to the total orbital angular momentum projection $M_z$ and
electron and hole spins $S_e$, $S_h$, a new exact quantum number appears. This
oscillator quantum number, k, is related physically to the center of the
cyclotron motion of the complex as a whole. In the dipole approximation k is
strictly conserved in magneto-optical transitions. We discuss implications of
this new exact selection rule for internal intraband magneto-optical
transitions of charged excitons $X^-$ in quantum wells in B.


title:
Effective Field Theory of the Zero-Temperature Triangular-Lattice
  Antiferromagnet: A Monte Carlo Study

abstract:
  Using a Monte Carlo coarse-graining technique introduced by Binder et al., we
have explicitly constructed the continuum field theory for the zero-temperature
triangular Ising antiferromagnet. We verify the conjecture that this is a
gaussian theory of the height variable in the interface representation of the
spin model. We also measure the height-height correlation function and deduce
the stiffness constant. In addition, we investigate the nature of defect-defect
interactions at finite temperatures, and find that the two-dimensional Coulomb
gas scenario applies at low temperatures.


title: "Quadratic solitons" in nonlinear dynamiical latticess

abstract:
  We propose a lattice model, in both one- and multidimensional versions, which
may give rise to matching conditions necessary for the generation of solitons
through the second-harmonic generation. The model describes an array of
linearly coupled two-component dipoles in an anisotropic nonlinear host medium.
Unlike this discrete system, its continuum counterpart gives rise to the
matching conditions only in a trivial degenerate situation. A system of
nonlinear evolution equations for slowly varying envelope functions of the
resonantly coupled fundamental- and second-harmonic waves is derived. In the
one-dimensional case, it coincides with the standard system known in nonlinear
optics, which gives rise to stable solitons. In the multidimensional case, the
system prove to be more general than its counterpart in optics, because of the
anisotropy of the underlying lattice model.


title:
Collective modes and sound propagation in a p-wave superconductor:
  Sr$_2$RuO$_4$

abstract:
  There are five distinct collective modes in the recently discovered p-wave
superconductor Sr$_2$RuO$_4$; phase and amplitude modes of the order parameter,
clapping mode (real and imaginary), and spin wave. The first two modes also
exist in the ordinary s-wave superconductors, while the clapping mode with the
energy $\sqrt{2} \Delta(T)$ is unique to Sr$_2$RuO$_4$ and couples to the sound
wave. Here we report a theoretical study of the sound propagation in a two
dimensional p-wave superconductor. We identified the clapping mode and study
its effects on the longitudinal and transverse sound velocities in the
superconducting state. In contrast to the case of $^3$He, there is no resonance
absorption associated with the collective mode, since in metals $\omega/(v_F
|{\bf q}|) \ll 1$, where $v_F$ is the Fermi velocity, {\bf q} is the wave
vector, and $\omega$ is the frequency of the sound wave. However, the velocity
change in the collisionless limit gets modified by the contribution from the
coupling to the clapping mode. We compute this contribution and comment on the
visibility of the effect. In the diffusive limit, the contribution from the
collective mode turns out to be negligible. The behaviors of the sound velocity
change and the attenuation coefficient near $T_c$ in the diffusive limit are
calculated and compared with the existing experimental data wherever it is
possible. We also present the results for the attenuation coefficients in both
of the collisionless and diffusive limits at finite temperatures.


title: Cooper Pairing in Ultracold K-40 Using Feshbach Resonances

abstract:
  We point out that the fermionic isotope K-40 is a likely candidate for the
formation of Cooper pairs in an ultracold atomic gas. Specifically, in an
optical trap that simultaneously traps the spin states |9/2,-9/2> and
|9/2,-7/2>, there exists a broad magnetic field Feshbach resonance at B = 196
gauss that can provide the required strong attractive interaction between
atoms. An additional resonance, at B = 191 gauss, could generate p-wave pairing
between identical |9/2,-7/2> atoms. A Cooper-paired degenerate Fermi gas could
thus be constructed with existing ultracold atom technology.


title:
Nanoconstriction Microscopy of the Giant Magnetoresistance in
  Cobalt/Copper Spin Valves

abstract:
  We use nanometer-sized point contacts to a Co/Cu spin valve to study the
giant magnetoresistance (GMR) of only a few Co domains. The measured data show
strong device-to-device differences of the GMR curve, which we attribute to the
absence of averaging over many domains. The GMR ratio decreases with increasing
bias current. For one particular device, this is accompanied by the development
of two distinct GMR plateaus, the plateau level depending on bias polarity and
sweep direction of the magnetic field. We attribute the observed behavior to
current-induced changes of the magnetization, involving spin transfer due to
incoherent emission of magnons and self-field effects.


title:
Thermodynamics of a trapped Bose condensate with negative scattering
  length

abstract:
  We study the Bose-Einstein condensation (BEC) for a system of $^7Li$ atoms,
which have negative scattering length (attractive interaction), confined in a
harmonic potential. Within the Bogoliubov and Popov approximations, we
numerically calculate the density profile for both condensate and
non-condensate fractions and the spectrum of elementary excitations. In
particular, we analyze the temperature and number-of-boson dependence of these
quantities and evaluate the BEC transition temperature $T_{BEC}$. We calculate
the loss rate for inelastic two- and three-body collisions. We find that the
total loss rate is strongly dependent on the density profile of the condensate,
but this density profile does not appreciably change by increasing the thermal
fraction. Moreover, we study, using the quasi-classical Popov approximation,
the temperature dependence of the critical number $N_c$ of condensed bosons,
for which there is the collapse of the condensate. There are different regimes
as a function of the total number $N$ of atoms. For $N<N_c$ the condensate is
always metastable but for $N>N_c$ the condensate is metastable only for
temperatures that exceed a critical value $T_c$.


title:
Heat capacity and transport studies of the ferromagnetic superconductor
  RuSr2GdCu2O8

abstract:
  Resistivity, thermoelectric power and heat capacity are investigated in the
ferromagnetic superconductor RuSr2GdCu2O8 with and without Zn substitution. The
thermodynamic signatures of the ordering of the Ru moments and the paramagnetic
Gd moments as well as the onset of superconductivity are all clearly seen and
quantified. The materials are shown to exhibit bulk superconductivity which
coexists with spatially-uniform ferromagnetism. They appear to be typical
underdoped superconducting cuprates in which the pseudogap dominates
normal-state transport, thermodynamic and substitutional properties. However, a
field-induced increase in Tc could suggest some degree of triplet pairing.


title: Thermoelectric Response Near the Density Driven Mott Transition

abstract:
  We investigate the thermoelectric response of correlated electron systems
near the density driven Mott transition using the dynamical mean field theory.


title:
Commensurability, excitation gap and topology in quantum many-particle
  systems on a periodic lattice

abstract:
  Combined with Laughlin's argument on the quantized Hall conductivity,
Lieb-Schultz-Mattis argument is extended to quantum many-particle systems
(including quantum spin systems) with a conserved particle number, on a
periodic lattice in arbitrary dimensions. Regardless of dimensionality,
interaction strength and particle statistics (bose/fermi), a finite excitation
gap is possible only when the particle number per unit cell of the groundstate
is an integer.


title: Persistence exponent of the diffusion equation in epsilon dimensions

abstract:
  We consider the d-dimensional diffusion equation for a field phi(x,t) with
random initial condition, and observe that, when appropriately scaled, phi(0,t)
is Gaussian and Markovian in the limit d->0. This leads via the Majumdar-Sire
perturbation theory to a small-d expansion for the persistence exponent
theta(d). We find theta(d) = d/4 - 0.12065...d^{3/2} + ...


title:
Ground-state energy of a high-density electron gas in a strong magnetic
  field

abstract:
  The high-density electron gas in a strong magnetic field B and at zero
temperature is investigated. The quantum strong-field limit is considered in
which only the lowest Landau level is occupied. It is shown that the
perturbation series of the ground-state energy can be represented in analogy to
the Gell-Mann Brueckner expression of the ground-state energy of the field-free
electron gas. The role of the expansion parameter is taken by $r_B= (2/3 \pi^2)
(B/m^2) (\hbar r_S/e)^3$ instead of the field-free Gell-Mann Brueckner
parameter r_s.


title:
A Model for the Self-Organization of Microtubules Driven by Molecular
  Motors

abstract:
  We propose a two-dimensional model for the organization of stabilized
microtubules driven by molecular motors in an unconfined geometry. In this
model two kinds of dynamics are competing. The first one is purely diffusive,
with an interaction between the rotational degrees of freedom, the second one
is a local drive, dependent on microtubule polarity. As a result, there is a
configuration dependent driving field. Applying a molecular field
approximation, we are able to derive continuum equations. A study on the
solutions shows nonequilibrium steady states. The presence and stability of
such self-organized states are investigated in terms of entropy production.
Numerical simulations confirm analytical results.


title:
Bosonization Based on Bethe Ansatz Equations and Spin-Charge Separation
  in the Hubbard Model with Finite U

abstract:
  We develop a bosonization approach for one-dimensional models based on Bethe
ansatz equations. The operator formalism of the exact soluble models in the low
energy limit provides a systematic method to calculate the asymptotic
correlation functions. As examples with and without internal degrees of
freedom, the Calogero-Sutherland (C-S) model and the repulsive Hubbard model
are considered respectively. We verify that the low energy behavior of the C-S
model is controlled by two classes of c=1 conformal field theories, depending
on whether the C-S interactions are among bosons or among fermions. For the
Hubbard model, we show the explicit charge-spin separation at low energy for
arbitrary U>0. The low energy behavior of the system is described by the
(semi-) direct product of two independent Virasoro algebras with c=1.


title: Optimization Algorithms Based on Renormalization Group

abstract:
  Global changes of states are of crucial importance in optimization
algorithms. We review some heuristic algorithms in which global updates are
realized by a sort of real-space renormalization group transformation. Emphasis
is on the relationship between the structure of low-energy excitations and
``block-spins'' appearing in the algorithms. We also discuss the implication of
existence of a finite-temperature phase transition on the computational
complexity of the ground-state problem.


title:
Topological coupling of dislocations and magnetization vorticity in Spin
  Density Waves

abstract:
  The rich order parameter of Spin Density Waves allows for an unusual object
of a complex topological nature: a half-integer dislocation combined with a
semi-vortex of the staggered magnetization. It becomes energetically preferable
to ordinary dislocation due to enhanced Coulomb interactions in the
semiconducting regime. Generation of these objects changes the narrow band
noise frequency.


title:
Dynamical phase transitions in glasses induced by the ruggedness of the
  free energy landscape

abstract:
  We propose damage spreading (DS) as a tool to investigate the topological
features related to the ruggedness of the free energy landscape. We argue that
DS measures the positiveness of the largest Lyapunov exponent associated to the
basins of attraction visited by the system during its dynamical evolution. We
discuss recent results obtained in the framework of mode-coupling theory and
comment how to extend them to the study of realistic glasses. Preliminary
results are presented for purely repulsive soft-sphere glasses.


title: Magnetic field as a probe of gap energy scales in YBCO

abstract:
  Among high T_c materials, the YBCO (YBa_2Cu_3O_{7-x}) compounds are special
since they have superconducting chains as well as planes. We show that a
discontinuity in the density of states as a function of magnetic field may
appear at a new energy scale, characteristic of the chain and distinct from
that set by the d wave gap. This is observable in experimental studies of the
thermodynamical properties of these systems, such as the specific heat.


title: Nature of spin-charge separation

abstract:
  Quasiparticle properties are explored in an effective theory of the $t-J$
model which includes two important components: spin-charge separation and
unrenormalizable phase shift. We show that the phase shift effect indeed causes
the system to be a non-Fermi liquid as conjectured by Anderson on a general
ground. But this phase shift also drastically changes a conventional perception
of quasiparticles in a spin-charge separation state: an injected hole will
remain {\em stable} due to the confinement of spinon and holon by the phase
shift field despite the background is a spinon-holon sea. True {\em
deconfinement} only happens in the {\em zero-doping} limit where a bare hole
will lose its integrity and decay into holon and spinon elementary excitations.
The Fermi surface structure is completely different in these two cases, from a
large band-structure-like one to four Fermi points in one-hole case, and we
argue that the so-called underdoped regime actually corresponds to a situation
in between, where the ``gap-like'' effect is amplified further by a microscopic
phase separation at low temperature. Unique properties of the single-electron
propagator in both normal and superconducting states are studied by using the
equation of motion method. We also comment on some of influential ideas
proposed in literature related to the Mott-Hubbard insulator and offer a
unified view based on the present consistent theory.


title:
The energy-level statistics in the core of a vortex in a p-wave
  superconductor

abstract:
  In the presence of strong disorder, the statistics of quasiparticle levels in
the core of a vortex in a two-dimensional p-wave superconductor belongs to the
universality class B corresponding to the ensemble of orthogonal matrices in
odd dimensions. This novel universality class appears as a consequence of the
O(2) spin symmetry of p-wave pairing. It is preserved in the presence of random
disorder, of electromagnetic vector potential, and of an admixture of the
pairing of opposite chirality in the vortex core, but may be destroyed by
spin-orbit coupling and by Zeeman splitting.


title: Parity Effect in the Resonant Tunneling

abstract:
  A mechanism of the parity effect in the thermally assisted resonant tunneling
is proposed in the view point of nonadiabatic transitions of thermally excited
states. In this mechanism, alternating enhancement of the relaxation is
naturally understood as a general property of quantum relaxation of uniaxial
magnets at finite temperatures where appreciable populations are pumped up to
excited states. It is also found that the enhanced sequence depends on the
sweeping rate of the field.


title:
Metallic nonsuperconducting phase and d-wave superconductivity in
  Zn-substituted LaSrCuO

abstract:
  Measurements of the resistivity, magnetoresistance and penetration depth were
made on films of LaSrCuO with up to 12 at.% of Zn substituted for the Cu. The
results show that the quadratic temperature dependence of the inverse square of
the penetration depth, indicative of d-wave superconductivity, is not affected
by doping. The suppression of superconductivity leads to a metallic
nonsuperconducting phase, as expected for a pairing mechanism related to spin
fluctuations. The metal-insulator transition occurs in the vicinity of kFl~1,
and appears to be disorder-driven, with the carrier concentration unaffected by
doping.


title: Bogoliubov transformation for distinguishable particles

abstract:
  The Bogoliubov transformation is generally derived in the context of
identical bosons with the use of ``second quantized'' a and $a^{\dagger}$
operators (or, equivalently, in field theory). Here, we show that the
transformation, together with its characteristic energy spectrum, can also be
derived within the Hilbert space of distinguishable particles, obeying
Boltzmann statistics; in this derivation, ordinary dyadic operators play the
role usually played by the a and $a^{\dagger}$ operators; therefore, breaking
the symmetry of particle conservation is not necessary.


title: Coherent Control of Photocurrents in Graphene and Carbon Nanotubes

abstract:
  Coherent one photon ($2 \omega$) and two photon ($ \omega$) electronic
excitations are studied for graphene sheets and for carbon nanotubes using a
long wavelength theory for the low energy electronic states. For graphene
sheets we find that coherent superposition of these excitations produces a
polar asymmetry in the momentum space distribution of the excited carriers with
an angular dependence which depends on the relative polarization and phases of
the incident fields. For semiconducting nanotubes we find a similar effect
which depends on the square of the semiconducting gap, and we calculate its
frequency dependence.
  We find that the third order nonlinearity which controls the direction of the
photocurrent is robust for semiconducting t ubes and vanishes in the continuum
theory for conducting tubes. We calculate corrections to these results arising
from higher order crystal field effects on the band structure and briefly
discuss some applications of the theory.


title:
Critical Temperature and Nonextensivity in Long-range Interacting
  Lennard-Jones-like Fluids

abstract:
  Molecular dynamic simulations for systems with $D=2,3$ Lennard-Jones-like
interactions are studied. In the model, we assume that, at long distances, the
two-body attractive potential decays as $r^{-\alpha}$. Thermodynamic
extensivity (nonextensivity) is observed for $\alpha > D$ ($0\leq \alpha \leq
D$). Particular attention is payed to the liquid-gas critical point located, in
the temperature-pressure plane, at ($T_c,P_c$). ($T_c,P_c$) are, in the $N\to
\infty$ limit ($N\equiv$ number of molecules), {\em finite} for $\alpha > D$
and {\em diverge} for $\alpha \leq D$ (as $(\alpha - D)^{-1}$ for $\alpha/D \to
1 + 0$). However, the variables $T_c^* \equiv T_c/N^*$ and $P_c^* \equiv
P_c/N^*$ with $N^* \equiv [N^{1-\alpha/D} -1]/[1-\alpha/D]$ remain {\em finite
for all} $\alpha$. Thus, the extensive and nonextensive regions become unified,
as recently conjectured. These results should be useful for discussing
gravitation and some special fluids