title:
Experimental evidence of a fractal dissipative regime in high-T_c
  superconductors

abstract:
  We report on our experimental evidence of a substantial geometrical
ingredient characterizing the problem of incipient dissipation in high-T_c
superconductors(HTS): high-resolution studies of differential
resistance-current characteristics in absence of magnetic field enabled us to
identify and quantify the fractal dissipative regime inside which the actual
current-carrying medium is an object of fractal geometry. The discovery of a
fractal regime proves the reality and consistency of critical-phenomena
scenario as a model for dissipation in inhomogeneous and disordered HTS, gives
the experimentally-based value of the relevant finite-size scaling exponent and
offers some interesting new guidelines to the problem of pairing mechanisms in
HTS.


title: Structural relaxation in atomic clusters: Master equation dynamics

abstract:
  The role of the potential energy landscape in determining the relaxation
dynamics of model clusters is studied using a master equation. Two types of
energy landscape are examined: a single funnel, as exemplified by 13-atom Morse
clusters, and the double funnel landscape of the 38-atom Lennard-Jones cluster.
Interwell rate constants are calculated using Rice-Ramsperger-Kassel-Marcus
theory within the harmonic approximation, but anharmonic model partition
functions are also considered. Decreasing the range of the potential in the
Morse clusters is shown to hinder relaxation towards the global minimum, and
this effect is related to the concomitant changes in the energy landscape. The
relaxation modes that emerge from the master equation are interpreted and
analysed to extract interfunnel rate constants for the Lennard-Jones cluster.
Since this system is too large for a complete characterization of the energy
landscape, the conditions under which the master equation can be applied to a
limited database are explored. Connections are made to relaxation processes in
proteins and structural glasses.


title:
Transport spin polarization of Ni_xFe_{1-x}: electronic kinematics and
  band structure

abstract:
  We present measurements of the transport spin polarization of Ni_xFe_{1-x}
(0<x<1) using the recently-developed Point Contact Andreev Reflection
technique, and compare them with our first principles calculations of the spin
polarization for this system. Surpisingly, the measured spin polarization is
almost composition-independent. The results clearly demonstrate that the sign
of the transport spin polarization does not coincide with that of the
difference of the densities of states at the Fermi level. Calculations indicate
that the independence of the spin polarization of the composition is due to
compensation of density of states and Fermi velocity in the s- and d- bands.


title:
Comparison of the fluctuation influence on the resistive properties of
  the mixed state of BiSrCaCuO and of thin films of conventional superconductor

abstract:
  The resistive properties of layered HTSC BiSrCaCuO in the mixed state are
compared with those of thin films of conventional superconductors with weak
disorders (amorphous Nb_{1-x}0_{x} films) and with strong disorders
(Nb_{1-x}O_{x} films with small grain structure). The excess conductivity is
considered as a function of superconducting electron density and phase
coherence length. It is shown that the transition to the Abrikosov state
differs from the ideal case both in BiSrCaCuO and Nb_{1-x}O_{x} films, i.e. the
appearance of long-range phase coherence is continuous transition in both
cases. The quantitative difference between thin films with weak and strong
disorders is greater than the one between layered HTSC and conventional
superconductors, showing that the dimensionality of the system, rather than the
critical temperature, is the key factor ruling fluctuation effects


title: Constant rate linear interface depinning and self organized criticality

abstract:
  The precise determination of the universality classes in self-organized
critical phenomena (SOC) is still an unsolved problem. Different SOC models
like sandpile, linear interface depinning, and the Barkhausen effect have been
investigated independently. In the present work we demonstrate that these
models can all be mapped into a linear interface depinning model driven at
constant rate. The model is found to belong to the universality class of
constant force linear interface depinning above the depinning transition, with
an upper critical dimension d_c=4. Results are compared with numerical
simulations, experiments, and previous theoretical works reported in the
literature. In this way we demonstrate a precise connection between different
SOC models which display the same universal beha


title:
Pseudo-Gap Phase, the Quantum-Critical Point and superconductivity in
  Copper-Oxide Metals

abstract:
  A systematic solution of a general model for Copper-Oxides reveals a line of
transitions $T = T_p (x)$ for $x$, the doping away from half-filling less than
a critical value, to a phase with broken time reversal and rotational symmetry
but with translational symmetry preserved. The single-particle spectrum in this
phase is calculated to have a gap of $d_{x^2 - y^2}$ symmetry. The properties
in this phase are compared to the properties of the so called ''pseudo-gap
phase'' in the Copper-Oxides. The fluctuations towards this phase promote
superconductivity which is either of the $d_{x^2-y^2}$ or the generalised
s-symmetry depending on whether the projected density of states at the chemical
potential is larger in the $d_{x^2-y^2}$ channel, as in the hole-doped
copper-oxides, or in the s-wave channel.


title: On the Structure of the Bose-Einstein Condensate Ground State

abstract:
  We construct a macroscopic wave function that describes the Bose-Einstein
condensate and weakly excited states, using the su(1,1) structure of the
mean-field hamiltonian, and compare this state with the experimental values of
second and third order correlation functions.


title:
Improved numerical approach for time-independent Gross-Pitaevskii
  nonlinear Schroedinger equation

abstract:
  In the present work, we improve a numerical method, developed to solve the
Gross-Pitaevkii nonlinear Schroedinger equation. A particular scaling is used
in the equation, which permits to evaluate the wave-function normalization
after the numerical solution. We have a two point boundary value problem, where
the second point is taken at infinity. The differential equation is solved
using the shooting method and Runge-Kutta integration method, requiring that
the asymptotic constants, for the function and its derivative, are equal for
large distances. In order to obtain fast convergence, the secant method is
used.


title: ``Weather'' Records: Musings on Cold Days after a Long Hot Indian Summer

abstract:
  We present a simple, pedagogical introduction to the statistics of extreme
values. Motivated by a string of record high temperatures in December 1998, we
consider the distribution, averages and lifetimes for a simplified model of
such ``records.'' Our ``data'' are sequences of independent random numbers all
of which are generated from the same probability distribution. A remarkable
universality emerges: a number of results, including the lifetime histogram,
are universal, that is, independent of the underlying distribution.


title: Stochastic model of hysteresis

abstract:
  The methods of the probability theory have been used in order to build up a
new model of hysteresis. It turns out that the reversal points of the control
parameter (e. g., the magnetic field) are Markov points which determine the
stochastic evolution of the process. It has been shown that the branches of the
hysteresis loop are converging to fixed limit curves when the number of cyclic
back-and-forth variations of the control parameter between two consecutive
reversal points is large enough. This convergence to limit curves gives a clear
explanation of the accommodation process. The accommodated minor loops show the
return-point memory property but this property is obviously absent in the case
of non-accommodated minor loops which are not congruent and generally not
closed. In contrast to the traditional Preisach model the reversal point
susceptibilities are non-zero finite values. The stochastic model can provide a
good approximation of the Raylaigh quadratic law when the external parameter
varies between two sufficiently small values.


title:
Unexpected scenario of glass transition in polymer globules: an exactly
  enumerable model

abstract:
  We introduce a lattice model of glass transition in polymer globules. This
model exhibits a novel scenario of ergodicity breaking in which the disjoint
regions of phase space do not arise uniformly, but as small chambers whose
number increases exponentially with polymer density. Chamber sizes obey power
law distribution, making phase space similar to a fractal foam. This clearly
demonstrates the importance of the phase space geometry and topology in
describing any glass-forming system, such as semicompact polymers during
protein folding.


title: Random walks in the space of conformations of toy proteins

abstract:
  Monte Carlo dynamics of the lattice 48 monomers toy protein is interpreted as
a random walk in an abstract (discrete) space of conformations. To test the
geometry of this space, we examine the return probability $P(T)$, which is the
probability to find the polymer in the native state after $T$ Monte Carlo
steps, provided that it starts from the native state at the initial moment.
Comparing computational data with the theoretical expressions for $P(T)$ for
random walks in a variety of different spaces, we show that conformational
spaces of polymer loops may have non-trivial dimensions and exhibit negative
curvature characteristic of Lobachevskii (hyperbolic) geometry.


title: H_c_3 for a thin-film superconductor with a ferromagnetic dot

abstract:
  We investigate the effect of a ferromagnetic dot on a thin-film
superconductor. We use a real-space method to solve the linearized
Ginzburg-Landau equation in order to find the upper critical field, H_c_3. We
show that H_c_3 is crucially dependent on dot composition and geometry, and may
be significantly greater than H_c_2. H_c_3 is maximally enhanced when (1) the
dot saturation magnetization is large, (2) the ratio of dot thickness to dot
diameter is of order one, and (3) the dot thickness is large.


title:
Transport and Magnetic properties of laser ablated La0.7Ce0.3MnO3 films
  on LaAlO3: Effect of oxygen pressure, sample thickness and co-doping with Ca

abstract:
  La0.7Ce0.3MnO3 is a relatively new addition in the family of colossal
magnetoresistive manganites where the cerium ion is believed to be in the Ce4+
state. In this paper we report an extensive study the magnetotransport
properties of laser ablated La0.7Ce0.3MnO3 films on LaAlO3 with variation in
ambient oxygen pressure during growth and film thickness. We observe that the
transport and magnetic properties of the film depend on the interplay between
oxygen pressure, surface morphology, film thickness and epitaxial strain. The
films were characterized by x-ray diffraction on a 4-circle x-ray goniometer.
We observe an increase in the metal-insulator transition temperature with
decreasing oxygen pressure. This is in direct contrast with the oxygen pressure
dependence of La0.7Ca-0.3MnO-3 films suggesting the electron doped nature of
the La0.7Ce0.3MnO3 system. With decreasing film thickness we observe an
increase in the metal-insulator transition temperature. This is associated with
a compression of the unit cell in the a-b plane due to epitaxial strain. When
the system is co-doped with 50% Ca at the Ce site the system
(La0.7Ca0.15Ce0.15MnO3) is driven into a insulating state suggesting that the
electrons generated by Ce4+ is compensated by the holes generated by Ca2+
valence thus making the average valence at the rare-earth site 3+ as in the
parent material LaMnO3.


title: Pump Built-in Hamiltonian Method for Pump-Probe Spectroscopy

abstract:
  We propose a new method of calculating nonlinear optical responses of
interacting electronic systems. In this method, the total Hamiltonian (system +
system-pump interaction) is transformed into a different form that (apparently)
does not have a system-pump interaction. The transformed Hamiltonian, which we
call the pump built-in Hamiltonian, has parameters that depend on the strength
of the pump beam. Using the pump built-in Hamiltonian, we can calculate
nonlinear responses (responses to probe beams as a function of the pump beam)
by applying the {\em linear} response theory. We demonstrate the basic idea of
this new method by applying it to a one-dimensional, two-band model, in the
case the pump excitation is virtual (coherent excitation). We find that the
exponent of the Fermi edge singularity varies with the pump intensity.


title:
A simple solid-on-solid model of epitaxial thin films growth: surface
  roughness and dynamics

abstract:
  The random deposition model must be enriched to reflect the variety of
surface roughness due to some material characteristics of the film growing by
vacuum deposition or sputtering. The essence of the computer simulation in this
case is to account for possible surface migration of atoms just after the
deposition, in connection with binding energy between atoms (as the mechanism
provoking the diffusion) and/or diffusion energy barrier. The interplay of
these two factors leads to different morphologies of the growing surfaces from
flat and smooth ones, to rough and spiky ones. In this paper we extended our
earlier calculation by applying some extra diffusion barrier at the edges of
terrace-like structures, known as Ehrlich-Schwoebel barrier. It is
experimentally observed that atoms avoid descending when the terrace edge is
approach and these barriers mimic this tendency. Results of our Monte Carlo
computer simulations are discussed in terms of surface roughness, and compared
with other model calculations and some experiments from literature. The power
law of the surface roughness $\sigma$ against film thickness $t$ was confirmed.
The nonzero minimum value of the growth exponent $\beta$ near 0.2 was obtained
which is due to the limited range of the surface diffusion and the
Ehrlich-Schwoebel barrier. Observations for different diffusion range are also
discussed. The results are also confronted with some deterministic growth
models.


title:
A simple solid-on-solid model of epitaxial thin films growth: surface
  morphology anisotropy

abstract:
  In this paper we present a generalization of a simple solid-on-solid
epitaxial model of thin films growth, when surface morphology anisotropy is
provoked by anisotropy in model control parameters: binding energy and/or
diffusion barrier. The anisotropy is discussed in terms of the height-height
correlation function. It was experimentally confirmed that the difference in
diffusion barriers yields anisotropy in morphology of the surface. We got
antisymmetric correlations in the two in-plane directions for antisymmetric
binding.


title:
A simple solid-on-solid model of epitaxial thin films growth:
  inhomogeneous multilayered sandwiches

abstract:
  In this work a simple solid-on-solid (SOS) model of inhomogeneous films
epitaxial growth is presented. The results of the computer simulations based on
the random deposition (RD) enriched by a local relaxation which tends to
maximize the number of a particle-particle lateral bonds (PPLB) against
barriers blocking diffusion are presented. The influence of strength of the
atoms interactions and barriers for diffusion on film roughness and possible
bridges between the layers in tri-layered sandwich system are considered. For
magnetic layers with a nonmagnetic spacer the bridging is responsible for
direct magnetic coupling between layers. Also variations of the spacer
thickness, when scanning the film surface, is essential for uniformity of the
magnetic coupling between the layers. Number of bridges for very thin spacer,
and variation of the spacer thickness are discussed in this work.


title:
Fermi liquid theory of electronic topological transitions and screening
  anomalies in metals

abstract:
  General expressions for the contributions of the Van Hove singularity (VHS)in
the electron density of states to the thermodynamic potential $\Omega are
obtained in the framework of microscopic Fermi liquid theory. The
renormalization of the singularities in $\Omega connected with the Lifshitz
electronic topological transition (ETT) is found. Screening anomalies due to
virtual transitions between VHS and the Fermi level are considered. It is shown
that, in contrast with the one-particle picture of ETT, the singularities in
$\Omega turns out to be two-sided for interacting electrons.


title:
Statistical Physics of the Jamming Transition: The Search for Simple
  Models

abstract:
  We investigate universal features of the jamming transition in granular
materials, colloids and glasses. We show that the jamming transition in these
systems has common features: slowing of response to external perturbation, and
the onset of structural heterogeneities.


title:
Topological spin excitations of Heisenberg antiferromagnets in two
  dimensions

abstract:
  In this paper we discuss the construction and the dynamics of vortex-like
topological spin excitations in the Schwinger-boson description of Heisenberg
antiferromagnets in two dimensions. The topological spin excitations are Dirac
fermions (with gap) when spin value $S$ is a half-integer. Experimental and
theoretical implications of these excitations are being investigated.


title: Finite Temperature Density Instability at High Landau Level Occupancy

abstract:
  We study here the onset of charge density wave instabilities in quantum Hall
systems at finite temperature for Landau level filling $\nu>4$. Specific
emphasis is placed on the role of disorder as well as an in-plane magnetic
field. Beyond some critical value, disorder is observed to suppress the charge
density wave melting temperature to zero. In addition, we find that a
transition from perpendicular to parallel stripes (relative to the in-plane
magnetic field) exists when the electron gas thickness exceeds $\approx 60$\AA.
The perpendicular alignment of the stripes is in agreement with the
experimental finding that the easy conduction direction is perpendicular to the
in-plane field.


title:
Mixed Charge-Spin Response Functions of an Arbitrarily Polarized
  Electron Gas

abstract:
  In this paper, using different approaches we demonstrate the equality of the
two mixed charge-spin response functions of a spin-polarized electron gas when
orbital effects are negligible. Within a generalized STLS approximation we show
that the two mixed responses are equal. We also present arguments for the
equality of the two dynamic responses by considering a symmetry of the
effective screened interaction between two opposite spin electrons.
Furthermore, using the reflection symmetry of the system and the fact that the
hamiltonian is real we prove rigorously that the two responses coincide
identically.


title: Model for nucleation in GaAs homoepitaxy derived from first principles

abstract:
  The initial steps of MBE growth of GaAs on beta 2-reconstructed GaAs(001) are
investigated by performing total energy and electronic structure calculations
using density functional theory and a repeated slab model of the surface. We
study the interaction and clustering of adsorbed Ga atoms and the adsorption of
As_2 molecules onto Ga atom clusters adsorbed on the surface. The stable nuclei
consist of bound pairs of Ga adatoms, which originate either from dimerization
or from an indirect interaction mediated through the substrate reconstruction.
As_2 adsorption is found to be strongly exothermic on sites with a square array
of four Ga dangling bonds. Comparing two scenarios where the first As_2 gets
incorporated in the incomplete surface layer, or alternatively in a new added
layer, we find the first scenario to be preferable. In summary, the
calculations suggest that nucleation of a new atomic layer is most likely on
top of those surface regions where a partial filling of trenches in the surface
has occurred before.


title:
Exchange and Correlation Kernels at the Resonance Frequency --
  Implications for Excitation Energies in Density-Functional Theory

abstract:
  Specific matrix elements of exchange and correlation kernels in
time-dependent density-functional theory are computed. The knowledge of these
matrix elements not only constraints approximate time-dependent functionals,
but also allows to link different practical approaches to excited states,
either based on density-functional theory, or on many-body perturbation theory,
despite the approximations that have been performed to derive them.


title:
Screened Interaction and Self-Energy in an Infinitesimally Polarized
  Electron Gas via the Kukkonen-Overhauser Method

abstract:
  The screened electron-electron interaction $W_{\sigma, \sigma'}$ and the
electron self-energy in an infinitesimally polarized electron gas are derived
by extending the approach of Kukkonen and Overhauser. Various quantities in the
expression for $W_{\sigma, \sigma'}$ are identified in terms of the relevant
response functions of the electron gas. The self-energy is obtained from
$W_{\sigma, \sigma'}$ by making use of the GW method which in this case
represents a consistent approximation. Contact with previous calculations is
made.


title:
Circular Kinks on the Surface of Granular Material Rotated in a Tilted
  Spinning Bucket

abstract:
  We find that circular kinks form on the surface of granular material when the
axis of rotation is tilted more than the angle of internal friction of the
material. Radius of the kinks is measured as a function of the spinning speed
and the tilting angle. Stability consideration of the surface results in an
explanation that the kink is a boundary between the inner unstable and outer
stable regions. A simple cellular automata model also displays kinks at the
stability boundary.


title:
Formation and stability of self-assembled coherent islands in highly
  mismatched heteroepitaxy

abstract:
  We study the energetics of island formation in Stranski-Krastanow growth
within a parameter-free approach. It is shown that an optimum island size
exists for a given coverage and island density if changes in the wetting layer
morphology after the 3D transition are properly taken into account. Our
approach reproduces well the experimental island size dependence on coverage,
and indicates that the critical layer thickness depends on growth conditions.
The present study provides a new explanation for the (frequently found) rather
narrow size distribution of self-assembled coherent islands.


title: Random Energy Model at Complex Temperatures

abstract:
  The complete phase diagram of Random Energy Model (REM) is obtained for
complex temperatures using the method proposed by Derrida. We find the density
of zeroes for statistical sum. Then the method is applied to Generalized Random
Energy Model (GREM). This allows us to propose new analytical method for
investigating zeroes of statistical sum for finite-dimensional systems.


title:
Thermodynamic functions within the van Hove BCS model: Symmetry mixing
  effects

abstract:
  All the new layer perovskite superconductors seem to show a phenomenon of
symmetry mixing with repect to the order parameter. An analysis of the
different alternative of mixing and how far could them be presented is carried
out. For the particular case of s+id symmetry of the gap, the temperature
dependence of the specific heat ($C_{es}$) and the thermodynamic critical
magnetic field ($H_{c}$) are calculated. A double peak transition is observed
on $C_{es}(T)$ in the mixed regime while the single peak behavior is recovered
for a purely symmetric state (s or d). $C_{es}$ presents a quadratic law at low
tempeartures for a d-wave gap and for the s-wave one the typical exponential
attenuation. The temperature dependence of $H_{c}$ shows a clear phase
transition of second order at temperatures where the d-wave component becomes
negligible. A comparison with other results and experiments is done.


title: Study of Vortex Avalanches using the Bassler-Paczuski Model

abstract:
  We have carried out a model calculation of the flux noise produced by vortex
avalanches in a Type-II superconductor, using a simple kinetic model proposed
by Bassler and Paczuski. Over a broad range of frequencies, we find that the
flux noise $S_{\Phi}(\omega)$ has a power-law dependence on frequency,
$S_{\Phi}(\omega) \sim \omega^{-s}$, with $s \sim 1.4$ in reasonable agreement
with experiment. In addition, for small lattices, the calculated
$S_{\Phi}(\omega)$ has a high-frequency knee, which is seen in some
experiments, and which is due to the finite lattice size. Deviations between
calculation and experiment are attributed mostly to uncertainties in the
measured critical current densities and pinning strengths of the experimental
samples.


title: Stationary state in a two-temperature model with competing dynamics

abstract:
  A two-dimensional half-filled lattice gas model with nearest-neighbor
attractive interaction is studied where particles are coupled to two thermal
baths at different temperatures $T_1$ and $T_2$. The hopping of particles is
governed by the heat bath at temperature $T_1$ with probability $p$ and the
other heat bath $(T_2)$ with probability $1-p$ independently of the hopping
direction. On a square lattice the vertical and horizontal interfaces become
unstable while interfaces are stable in the diagonal directions. As a
consequence, particles condense into a tilted square in the novel ordered
state. The $p$-dependence of the resulting nonequilibrium stationary state is
studied by Monte Carlo simulation and dynamical mean-field approximation as
well.


title:
Coexistence of native and denatured phases in a single protein-like
  molecule

abstract:
  In order to understand the nuclei which develop during the course of protein
folding and unfolding, we examine phase segregation of a single heteropolymer
chain which occurs in equilibrium. These segregated conformations are
characterized by a nucleus of monomers which are superimposable upon the native
conformation. We computationally generate the phase segregation by applying a
``folding pressure,'' or adding an energetic bonus for native monomer-monomer
contacts. The computer models reveal a fundamental difference in the nucleation
process between heteropolymeric and the more familiar vapor-liquid systems: in
a polymer system, some nuclei hinder folding via topological constraints and
must be partially destroyed in order for folding to proceed. To illustrate this
finding, we examine the kinetics of protein unfolding in the long chain limit
through scaling arguments. We find that because of the topological constraints,
the critical nucleus size is of the order of the entire chain size so that
unfolding time scales as $\exp [c N^{2/3} ]$, where $N$ and $c$ are the chain
length and a constant.


title: A new method for analyzing ground-state landscapes: ballistic search

abstract:
  A ``ballistic-search'' algorithm is presented which allows the identification
of clusters (or funnels) of ground states in Ising spin glasses even for
moderate system sizes. The clusters are defined to be sets of states, which are
connected in state-space by chains of zero-energy flips of spins. The technique
can also be used to estimate the sizes of such clusters. The performance of the
method is tested with respect to different system sizes and choices of
parameters. As an application the ground-state funnel structure of
two-dimensional +or- J spin glasses of systems up to size L=20 is analyzed by
calculating a huge number of ground states per realization. A T=0 entropy per
spin of s_0=0.086(4)k_B is obtained.


title: Influence of a knot on the strength of a polymer strand

abstract:
  Many experiments have been done to determine the relative strength of
different knots, and these show that the break in a knotted rope almost
invariably occurs at a point just outside the `entrance' to the knot. The
influence of knots on the properties of polymers has become of great interest,
in part because of their effect on mechanical properties. Knot theory applied
to the topology of macromolecules indicates that the simple trefoil or
`overhand' knot is likely to be present with high probability in any long
polymer strand. Fragments of DNA have been observed to contain such knots in
experiments and computer simulations. Here we use {\it ab initio} computational
methods to investigate the effect of a trefoil knot on the breaking strength of
a polymer strand. We find that the knot weakens the strand significantly, and
that, like a knotted rope, it breaks under tension at the entrance to the knot.


title: Carbon films with a novel sp2 network structure

abstract:
  Laser-Arc evaporation of a graphite target has been used to deposit carbon
films that exhibit high hardness (45 GPa) and elastic recovery (85%). High
Resolution Electron Microscopy (HREM) and Electron Energy Loss Spectroscopy
(EELS) were subsequently used to study the microstructure and bonding of the
resultant layers. The structure of the films from HREM is seen to consist of a
dense array of parallel curved graphene sheet segments packed in various
orientations. EELS reveals that the films are comprised of mainly sp2 bonded
carbon. The results suggest that a new form of carbon thin film with
fullerene-like structure can be realised. In order to explain how a
predominantly sp2 bonded material can exhibit such a high hardness, a simple
model is proposed to correlate the excellent mechanical properties with the
observed structure.


title: Infinite characteristic length on small-world systems

abstract:
  It was recently claimed that on d-dimensional small-world networks with a
density p of shortcuts, the typical separation s(p) ~ p^{-1/d} between
shortcut-ends is a characteristic length for shortest-paths{cond-mat/9904419}.
This contradicts an earlier argument suggesting that no finite characteristic
length can be defined for bilocal observables on these systems
{cont-mat/9903426}. We show analytically, and confirm by numerical simulation,
that shortest-path lengths \ell(r) behave as \ell(r) ~ r for r < r_c, and as
\ell(r) ~ r_c for r > r_c, where r is the Euclidean separation between two
points and r_c(p,L) = p^{-1/d} log(L^dp) is a characteristic length. This shows
that the mean separation s between shortcut-ends is not a relevant length-scale
for shortest-paths. The true characteristic length r_c(p,L) diverges with
system size L no matter the value of p. Therefore no finite characteristic
length can be defined for small-world networks in the thermodynamic limit.


title:
Invariant spin coherent states and the theory of quantum antiferromagnet
  in a paramagnetic phase

abstract:
  The consistent theory of the Heisenberg quantum antiferromagnet in the
disordered phase with short range antiferromagnetic order was developed on the
basis of the path integral for the spin coherent states. We have presented the
Lagrangian of the theory in a form which is explicitly invariant under
rotations and have found natural variables in the term of which one can
construct a natural perturbation theory. The short wave spin fluctuations are
similar to the spin wave theory ones, and the long wave spin fluctuations are
governed by the nonlinear sigma model. We have also demonstrated that the short
wave spin fluctuations have to be considered accurately in the framework of the
discrete version in time of the path integral. In the framework of our approach
we have obtained the response function for the spin fluctuations for the whole
region of the frequency $\omega$ and the wave vector ${\bf k}$ and have
calculated the free energy of the system.


title:
Magnon Broadening Effect by Magnon-Phonon Interaction in Colossal
  Magnetoresistance Manganites

abstract:
  In order to study the magnetic excitation behaviors in colossal
magnetoresistance manganites, a magnon-phonon interacting system is
investigated. Sudden broadening of magnon linewidth is obtained when a magnon
branch crosses over an optical phonon branch. Onset of the broadening is
approximately determined by the magnon density of states. Anomalous magnon
damping at the brillouine zone boundary observed in low Curie temperature
manganites is explained.


title: Ehrlich-Schwoebel barrier controlled slope selection in epitaxial growth

abstract:
  We examine the step dynamics in a 1+1 dimensional model of epitaxial growth
based on the BCF-theory. The model takes analytically into account the
diffusion of adatoms, an incorporation mechanism and an Ehrlich-Schwoebel
barrier at step edges. We find that the formation of mounds with a stable slope
is closely related to the presence of an incorporation mechanism. We confirm
this finding using a Solid-On-Solid model in 2+1 dimensions. In the case of an
infinite step edge barrier we are able to calculate the saturation profile
analytically. Without incorporation but with inclusion of desorption and
detachment we find a critical flux for instable growth but no slope selection.
In particular, we show that the temperature dependence of the selected slope is
solely determined by the Ehrlich-Schwoebel barrier which opens a new
possibility in order to measure this fundamental barrier in experiments.


title: Ellipsoidal deformation of vertical quantum dots

abstract:
  Addition energy spectra at 0 T of circular and ellipsoidally deformed
few-electron vertical quantum dots are measured and compared to results of
model calculations within spin-density functional theory. Because of the
rotational symmetry of the lateral harmonic confining potential, circular dots
show a pronounced shell structure. With the lifting of the single- particle
level degeneracies, even a small deformation is found to radically alter the
shell structure leading to significant modifications in the addition energy
spectra. Breaking the circular symmetry with deformation also induces changes
in the total spin. This "piezo-magnetic" behavior of quantum dots is discussed,
and the addition energies for a set of realistic deformation parameters are
provided. For the case of the four-electron ground state at 0 T, a spin-triplet
to spin-singlet transition is predicted, i.e. Hund's first rule no longer
applies. Application of a magnetic field parallel to the current confirms that
this is the case, and also suggests that the anisotropy of an elliptical dot,
in practice, may be higher than that suggested by the geometry of the device
mesa in which the dot is located.


title: Coulomb Blockade Fluctuations in Disordered Quantum Dots

abstract:
  We discuss some recent results on the statistics of the Coulomb Blockade in
disordered quantum dots containing spinless interacting fermions using the
self-consistent Hartree-Fock approximation. We concentrate on the regime r_s
>~1, with finite dimensionless conductance g. We present significantly
different results for the cases of a Coulomb and a nearest-neighbour bare
interaction. We show that neglecting rearrangements when the particle number is
changed (Koopmans' approximation) can lead to large errors, and show how the
spectral statistics of the self-consistent single particle orbitals evolve with
the interaction strength.


title:
Effects of c-axis Hopping in the Interlayer Tunneling Model of High-Tc
  Layered Cuprates

abstract:
  We consider the interlayer pair-tunneling model for layered cuprates,
including an effective single particle hopping along the c-axis. A
phenomenological suppression of the c-axis hopping matrix element, by the
pseudogap in cuprate superconductors, is incorporated. At optimal doping,
quantities characteristic to the superconducting state, such as the transition
temperature and the superconducting gap are calculated. Results from our
calculations are consistent with the experimental observations with the
noteworthy point that, the superconducting gap as a function of temperature
shows excellent match to the experimental data. Predictions within the model,
regarding T_c variation with interlayer coupling, are natural outcomes which
could be tested further.


title:
Critical renormalized coupling constants in the symmetric phase of the
  Ising models

abstract:
  Using a novel finite size scaling Monte Carlo method, we calculate the four,
six and eight point renormalized coupling constants defined at zero momentum in
the symmetric phase of the three dimensional Ising system. The results of the
2D Ising system that were directly measured are also reported. Our values of
the six and eight point coupling constants are significantly different from
those obtained from other methods.


title:
Ballistic Four-Terminal Josephson Junction: Bistable States and Magnetic
  Flux Transfer

abstract:
  The macroscopic quantum interference effects in ballistic Josephson
microstructures are investigated. The studied system consists of four bulk
superconductors (terminals) which are weakly coupled through the mesoscopic
rectangular normal metal (two dimensional electron gas). We show that nonlocal
electrodynamics of ballistic systems leads to specific current-phase relations
for the mesoscopic multiterminal Josephson junction. The nonlocal coupling of
supercurrents produces the "dragging" effect for phases of the superconducting
order parameter in different terminals. The composite Josephson junction, based
on this effect, exhibits the two -level system behaviour controlled by the
external magnetic flux. The effect of magnetic flux transfer in a system of
nonlocally coupled superconducting rings is studied.


title: Dynamics of a Ring of Diffusively Coupled Lorenz Oscillators

abstract:
  We study the dynamics of a finite chain of diffusively coupled Lorenz
oscillators with periodic boundary conditions. Such rings possess infinitely
many fixed states, some of which are observed to be stable. It is shown that
there exists a stable fixed state in arbitrarily large rings for a fixed
coupling strength. This suggests that coherent behavior in networks of
diffusively coupled systems may appear at a coupling strength that is
independent of the size of the network.


title:
Suppression of metallic behavior in two dimensions by spin flip
  scattering

abstract:
  We study the effect of the disorder on the metallic behavior of a
two-dimensional electron system in silicon. The temperature dependence of
conductivity $\sigma (T)$ was measured for different values of substrate bias,
which changes both potential scattering and the concentration of
disorder-induced local magnetic moments. We find that the latter has a much
more profound effect on $d\sigma/dT$. In fact, the data suggest that in the
limit of $T\to 0$ the metallic behavior, as characterized by $d\sigma/dT < 0$,
is suppressed by an arbitrarily small amount of spin flip scattering by local
magnetic moments.


title:
Interesting history effect in the magnetotransport properies of
  La0.55Ho0.15Sr0.3MnOz films on LaAlO3

abstract:
  We report the magnetoresistance measurements of a highly oriented
La0.55Ho0.15Sr0.3MnOz film on LaAlO3 substrate. The film has a metal-insulator
transition around 200 K and shows pronounced thermomagnetic history effect in
its transport properties below 45 K at 7 Tesla. The irreversibility temperature
shifts to lower temperatures when the field is reduced. This behaviour is
opposite to the thermomagnetic history effect observed in the magnetisation. At
2.8 K one also observes a significant hysteresis in the resistance versus field
curve. We propose a qualitative explanation for these observations.


title:
The Potts Fully Frustrated model: Thermodynamics, percolation and
  dynamics in 2 dimensions

abstract:
  We consider a Potts model diluted by fully frustrated Ising spins. The model
corresponds to a fully frustrated Potts model with variables having an integer
absolute value and a sign. This model presents precursor phenomena of a glass
transition in the high-temperature region. We show that the onset of these
phenomena can be related to a thermodynamic transition. Furthermore this
transition can be mapped onto a percolation transition. We numerically study
the phase diagram in 2 dimensions (2D) for this model with frustration and {\em
without} disorder and we compare it to the phase diagram of $i)$ the model with
frustration {\em and} disorder and of $ii)$ the ferromagnetic model.
Introducing a parameter that connects the three models, we generalize the exact
expression of the ferromagnetic Potts transition temperature in 2D to the other
cases. Finally, we estimate the dynamic critical exponents related to the Potts
order parameter and to the energy.


title: Interference and Interaction in Multiwall Carbon Nanotubes

abstract:
  We report equilibrium electric resistance R and tunneling spectroscopy dI/dV
measurements obtained on single multiwall nanotubes contacted by four metallic
Au fingers from above. At low temperature quantum interference phenomena
dominate the magnetoresistance. The phase-coherence and elastic-scattering
lengths are deduced. Because the latter is of order of the circumference of the
nanotubes, transport is quasi-ballistic. This result is supported by a dI/dV
spectrum which is in good agreement with the density-of-states (DOS) due to the
one-dimensional subbands expected for a perfect single-wall tube. As a function
of temperature T the resistance increases on decreasing T and saturates at
approx. 1-10 K for all measured nanotubes. R(T) cannot be related to the
energy-dependent DOS of graphene but is mainly caused by interaction and
interference effects. On a relatively small voltage scale of order 10 meV, a
pseudogap is observed in dI/dV which agrees with Luttinger-Liquid theories for
nanotubes. Because we have used quantum diffusion based on Fermi-Liquid as well
as Luttinger-Liquid theory in trying to understand our results, a large
fraction of this paper is devoted to a careful discussion of all our results.


title:
The Finite Temperature Mott Transition in the Hubbard Model in Infinite
  Dimensions

abstract:
  We study the second order finite temperature Mott transition point in the
fully frustrated Hubbard model at half filling, within Dynamical Mean Field
Theory. Using quantum Monte Carlo simulations we show the existence of a finite
temperature second order critical point by explicitly demonstrating the
existence of a divergent susceptibility as well as by finding coexistence in
the low temperature phase. We determine the location of the finite temperature
Mott critical point in the (U,T) plane. Our study verifies and quantifies a
scenario for the Mott transition proposed in earlier studies (Reviews of Modern
Physics 68, 13, 1996) of this problem.


title: Topological doping and the stability of stripe phases

abstract:
  We analyze the properties of a general Ginzburg-Landau free energy with
competing order parameters, long-range interactions, and global constraints
(e.g., a fixed value of a total ``charge'') to address the physics of stripe
phases in underdoped high-Tc and related materials. For a local free energy
limited to quadratic terms of the gradient expansion, only uniform or
phase-separated configurations are thermodynamically stable. ``Stripe'' or
other non-uniform phases can be stabilized by long-range forces, but can only
have non-topological (in-phase) domain walls where the components of the
antiferromagnetic order parameter never change sign, and the periods of charge
and spin density waves coincide. The antiphase domain walls observed
experimentally require physics on an intermediate lengthscale, and they are
absent from a model that involves only long-distance physics. Dense stripe
phases can be stable even in the absence of long-range forces, but domain walls
always attract at large distances, i.e., there is a ubiquitous tendency to
phase separation at small doping. The implications for the phase diagram of
underdoped cuprates are discussed.


title: Cyclotron Resonance in the Layered Perovskite Superconductor Sr2RuO4

abstract:
  We have measured the cyclotron masses in Sr2RuO4 through the observation of
periodic-orbit-resonances - a magnetic resonance technique closely related to
cyclotron resonance. We obtain values for the alpha, beta and gamma Fermi
surfaces of (4.33+/-0.05)me, (5.81+/-0.03)me and (9.71+/-0.11)me respectively.
The appreciable differences between these results and those obtained from de
Haas- van Alphen measurements are attributable to strong electron-electron
interactions in this system. Our findings appear to be consistent with
predictions for a strongly interacting Fermi liquid; indeed, semi-quantitative
agreement is obtained for the electron pockets beta and gamma.


title: Effects of dimensionality and anisotropy on the Holstein polaron

abstract:
  We apply weak-coupling perturbation theory and strong-coupling perturbation
theory to the Holstein molecular crystal model in order to elucidate the
effects of anisotropy on polaron properties in D dimensions. The ground state
energy is considered as a primary criterion through which to study the effects
of anisotropy on the self-trapping transition, the self-trapping line
associated with this transition, and the adiabatic critical point. The effects
of dimensionality and anisotropy on electron-phonon correlations and polaronic
mass enhancement are studied, with particular attention given to the polaron
radius and the characteristics of quasi-1D and quasi-2D structures.
Perturbative results are confirmed by selected comparisons with variational
calculations and quantum Monte Carlo data.


title:
Erratum: ``Thermal properties of gauge fields common to anyon
  superconductors and spin liquids''

abstract:
  In this erratum to my article published in Physical Review B, vol. 51, pg.
9348 (1995), I produce the correct formula for the deconfinement temperature of
compact QED in two space dimensions at weak-coupling. The context is anyon
superconductivity and chiral spin-liquid physics. (Any claims of priority are
welcome.)


title:
Frenkel-Kontorova Model of Vacancy-Line Interactions on Ga/Si(112):
  Formalism

abstract:
  We describe in greater detail the exactly solvable microscopic model we have
developed for analyzing the strain-mediated interaction of vacancy lines in a
pseudomorphic adsorbate system (Phys. Rev. Lett., to appear). The model is
applied to Ga/Si(112) by extracting values for the microscopic parameters from
total-energy calculations. The results, which are in good agreement with
experimental observations, reveal an unexpectedly complex interplay between
compressive and tensile strain within the mixed Ga-Si surface layer.


title:
Scanning tunneling microscopy and spectroscopy at low temperatures of
  the (110) surface of Te doped GaAs single crystals

abstract:
  We have performed voltage dependent imaging and spatially resolved
spectroscopy on the (110) surface of Te doped GaAs single crystals with a low
temperature scanning tunneling microscope (STM). A large fraction of the
observed defects are identified as Te dopant atoms which can be observed down
to the fifth subsurface layer. For negative sample voltages, the dopant atoms
are surrounded by Friedel charge density oscillations. Spatially resolved
spectroscopy above the dopant atoms and above defect free areas of the GaAs
(110) surface reveals the presence of conductance peaks inside the
semiconductor band gap. The appearance of the peaks can be linked to charges
residing on states which are localized within the tunnel junction area. We show
that these localized states can be present on the doped GaAs surface as well as
at the STM tip apex.


title:
Phase diagram of an extended Kondo lattice model for manganites: the
  Schwinger-boson mean-field approach

abstract:
  We investigate the phase diagram of an extended Kondo lattice model for doped
manganese oxides in the presence of strong but finite Hund's coupling and
on-site Coulomb interaction. By means of the Schwinger-boson mean-field
approach, it is found that, besides magnetic ordering, there will be
non-uniform charge distributions, such as charge ordering and phase separation,
if the interaction between electrons prevails over the hybridization. Which of
the charge ordering and phase separation appears is determined by a competition
between effective repulsive and attractive interactions due to virtual
processes of electron hopping. Calculated results show that strong electron
correlations caused by the on-site Coulomb interaction as well as the finite
Hund's coupling play an important role in the magnetic ordering and charge
distribution at low temperatures.


title:
Lateral tunneling through the controlled barrier between edge channels
  in a two-dimentional electron system

abstract:
  We study the lateral tunneling through the gate-voltage-controlled barrier,
which arises as a result of partial elimination of the donor layer of a
heterostructure along a fine strip using an atomic force microscope, between
edge channels at the depletion-induced edges of a gated two-dimensional
electron system. For a sufficiently high barrier a typical current-voltage
characteristic is found to be strongly asymmetric and include, apart from a
positive tunneling branch, the negative branch that corresponds to the current
overflowing the barrier. We establish the barrier height depends linearly on
both gate voltage and magnetic field and we describe the data in terms of
electron tunneling between the outermost edge channels.


title: Collective oscillations of an interacting trapped Fermi gas

abstract:
  We calculate the effects of two-body interactions on the low frequency
oscillations of a normal Fermi gas confined in a harmonic trap. The mean field
contribution to the collective frequencies is evaluated in the collisionless
regime using a sum rule approach. We also discuss the transition between the
collisionless and hydrodynamic regime with special emphasis to the spin dipole
mode in which two atomic clouds occupying different spin states oscillate in
opposite phase. The spin dipole mode is predicted to be overdamped in the
hydrodynamic regime. The relaxation time is calculated as a function of
temperature and the effects of Fermi statistics are explicitly pointed out.


title:
On the interaction energy of 2D electron FQHE systems within the
  Chern-Simons approach

abstract:
  The interaction energy of the two-dimensional electron system in the region
of fractional quantum Hall effect is considered within the Chern-Simons
composite fermion approach. In the limit when Coulomb interaction is very small
comparing to the cyclotron energy the RPA results are obtained for the fillings
$\nu=1/3, 1/5, 2/3, 2/5, 3/7$ and compared with the exact diagonalization
results for small systems (extrapolated for infinite systems). They show very
poor agreement suggesting the need for looking for alternative approaches.


title:
Theory of the Metal-Paramagnetic Mott-Jahn-Teller Insulator Transition
  in A_4C_{60}

abstract:
  We study the unconventional insulating state in A_4C_{60} with a variety of
approaches, including density functional calculations and dynamical mean-field
theory. While the former predicts a metallic state, in disagreement with
experiment, the latter yields a (paramagnetic) Mott-Jahn-Teller insulator. In
that state, conduction between molecules is blocked by on-site Coulomb
repulsion, magnetism is suppressed by intra-molecular Jahn-Teller effect, and
important excitations (such as optical and spin gap) should be essentially
intra-molecular. Experimental gaps of 0.5 eV and 0.1 eV respectively compare
well with molecular ion values, in agreement with this picture.


title:
Optimum ground states of generalized Hubbard models with next-nearest
  neighbour interaction

abstract:
  We investigate the stability domains of ground states of generalized Hubbard
models with next-nearest neighbour interaction using the optimum groundstate
approach. We focus on the $\eta$-pairing state with momentum P=0 and the fully
polarized ferromagnetic state at half-filling. For these states exact lower
bounds for the regions of stability are obtained in the form of inequalities
between the interaction parameters. For the model with only nearest neighbour
interaction we show that the bounds for the stability regions can be improved
by considering larger clusters. Additional next-nearest neighbour interactions
can lead to larger or smaller stability regions depending on the parameter
values.


title: Protein Ground State Candidates in a Simple Model: An Exact Enumeration

abstract:
  The concept of the reduced set of contact maps is introduced. Using this
concept we find the ground state candidates for Hydrophobic-Polar lattice model
on a two dimensional square lattice. Using these results we exactly enumerate
the native states of all proteins for a wide range of energy parameters. In
this way, we show that there are some sequences, which have an absolute native
state. Moreover, we study the scale-dependence of the number of the members of
the reduced set, the number of ground state candidates, and the number of
perfectly stable sequences by comparing the results for sequences with lengths
of 6 up to 20.


title:
Influence of resonant tunneling on the imaging of atomic defects on
  InAs(110) surfaces by low-temperature scanning tunneling microscopy

abstract:
  We have used a low-temperature scanning tunneling microscope (STM) to study
the surface of heavily doped semiconductor InAs crystals. The crystals are
cleaved in situ along the (110) plane. Apart from atomically flat areas, we
also observe two major types of atomic scale defects which can be identified as
S dopant atoms and as As vacancies, respectively. The strong bias voltage
dependence of the STM image of the impurities can be explained in terms of
resonant tunneling through localized states which are present near the
impurity.


title: Temperature cycling during the aging of a polymer glass

abstract:
  Temperature cycling is used to study of aging properties of PMMA dielectric
constant. If a negative temperature cycle is applied during the aging time the
relaxation dynamics is just delayed for a time equal to the cycle period. In
contrast this time shifting procedure cannot be applied to positive temperature
cycles . The analogies and differences with similar experiments done in other
aging systems, such as spin glasses, orientational glasses and supercooled
liquids, are discussed.


title: Failure time and microcrack nucleation

abstract:
  The failure time of samples of heterogeneous materials (wood, fiberglass) is
studied as a function of the applied stress. It is shown that in these
materials the failure time is predicted with a good accuracy by a model of
microcrack nucleation proposed by Pomeau. It is also shown that the crack
growth process presents critical features when the failure time is approached.


title: Matching fields of a long superconducting film

abstract:
  We obtain the vortex configurations, the matching fields and the
magnetization of a superconducting film with a finite cross section. The
applied magnetic field is normal to this cross section, and we use London
theory to calculate many of its properties, such as the local magnetic field,
the free energy and the induction for the mixed state. Thus previous similar
theoretical works, done for an infinitely long superconducting film, are
recovered here, in the special limit of a very long cross section.


title:
Vacancy-assisted domain-growth in asymmetric binary alloys: a Monte
  Carlo study

abstract:
  A Monte Carlo simulation study of the vacancy-assisted domain-growth in
asymmetric binary alloys is presented. The system is modeled using a
three-state ABV Hamiltonian which includes an asymmetry term, not considered in
previous works. Our simulated system is a stoichiometric two-dimensional binary
alloy with a single vacancy which evolves according to the vacancy-atom
exchange mechanism. We obtain that, compared to the symmetric case, the
ordering process slows down dramatically. Concerning the asymptotic behavior it
is algebraic and characterized by the Allen-Cahn growth exponent x=1/2. The
late stages of the evolution are preceded by a transient regime strongly
affected by both the temperature and the degree of asymmetry of the alloy. The
results are discussed and compared to those obtained for the symmetric case.


title: Orbits and phase transitions in the multifractal spectrum

abstract:
  We consider the one dimensional classical Ising model in a symmetric
dichotomous random field. The problem is reduced to a random iterated function
system for an effective field. The D_q-spectrum of the invariant measure of
this effective field exhibits a sharp drop of all D_q with q < 0 at some
critical strength of the random field. We introduce the concept of orbits which
naturally group the points of the support of the invariant measure. We then
show that the pointwise dimension at all points of an orbit has the same value
and calculate it for a class of periodic orbits and their so-called offshoots
as well as for generic orbits in the non-overlapping case. The sharp drop in
the D_q-spectrum is analytically explained by a drastic change of the scaling
properties of the measure near the points of a certain periodic orbit at a
critical strength of the random field which is explicitly given. A similar
drastic change near the points of a special family of periodic orbits explains
a second, hitherto unnoticed transition in the D_q-spectrum. As it turns out, a
decisive role in this mechanism is played by a specific offshoot. We
furthermore give rigorous upper and/or lower bounds on all D_q in a wide
parameter range. In most cases the numerically obtained D_q coincide with
either the upper or the lower bound. The results in this paper are relevant for
the understanding of random iterated function systems in the case of moderate
overlap in which periodic orbits with weak singularity can play a decisive
role.


title: One-dimensional fermions with incommensuration

abstract:
  We study the spectrum of fermions hopping on a chain with a weak
incommensuration close to dimerization; both q, the deviation of the wave
number from pi, and delta, the strength of the incommensuration, are small. For
free fermions, we use a continuum Dirac theory to show that there are an
infinite number of bands which meet at zero energy as q approaches zero. In the
limit that the ratio q/ \delta --> 0, the number of states lying inside the q=0
gap is nonzero and equal to 2 \delta /\pi^2. Thus the limit q --> 0 differs
from q=0; this can be seen clearly in the behavior of the specific heat at low
temperature. For interacting fermions or the XXZ spin-1/2 chain close to
dimerization, we use bosonization to argue that similar results hold; as q -->
0, we find a nontrivial density of states near zero energy. However, the limit
q --> 0 and q=0 give the same results near commensurate wave numbers which are
different from pi. We apply our results to the Azbel-Hofstadter problem of
electrons hopping on a two-dimensional lattice in the presence of a magnetic
field. Finally, we discuss the complete energy spectrum of noninteracting
fermions with incommensurate hopping by going up to higher orders in delta.


title: Kinematics of electrons near a Van Hove singularity

abstract:
  A two dimensional electronic system, where the Fermi surface is close to a
Van Hove singularity, shows a variety of weak coupling instabilities, and it is
a convenient model to study the interplay between antiferromagnetism and
anisotropic superconductivity. We present a detailed analysis of the kinematics
of the electron scattering in this model. The similitudes, and differences,
between a standard Renormalization Group approach and previous work based on
parquet summations of log$^2$ divergences are analyzed, with emphasis on the
underlying physical processes. General properties of the phase diagram are
discussed.


title: Electronic correlations on a metallic nanosphere

abstract:
  We consider the correlation functions in a gas of electrons moving within a
thin layer on the surface of nanosize sphere. A closed form of expressions for
the RKKY indirect exchange, superconducting Cooper loop and `density-density'
correlation function is obtained. The systematic comparison with planar results
is made, the effects of spherical geometry are outlined. The quantum coherence
of electrons leads to the enhancement of all correlations for the
points--antipodes on the sphere. This effect is lost when the radius of the
sphere exceeds the temperature coherence length.


title: Propagation and organization in lattice random media

abstract:
  We show that a signal can propagate in a particular direction through a model
random medium regardless of the precise state of the medium. As a prototype, we
consider a point particle moving on a one-dimensional lattice whose sites are
occupied by scatterers with the following properties: (i) the state of each
site is defined by its spin (up or down); (ii) the particle arriving at a site
is scattered forward (backward) if the spin is up (down); (iii) the state of
the site is modified by the passage of the particle, i.e. the spin of the site
where a scattering has taken place, flips ($\uparrow \Leftrightarrow \downarrow
$). We consider one dimensional and triangular lattices, for which we give a
microscopic description of the dynamics, prove the propagation of a particle
through the scatterers, and compute analytically its statistical properties. In
particular we prove that, in one dimension, the average propagation velocity is
$<c(q)> = 1/(3-2q)$, with $q$ the probability that a site has a spin
$\uparrow$, and, in the triangular lattice, the average propagation velocity is
independent of the scatterers distribution: $<c> = 1/8$. In both cases, the
origin of the propagation is a blocking mechanism, restricting the motion of
the particle in the direction opposite to the ultimate propagation direction,
and there is a specific re-organization of the spins after the passage of the
particle. A detailed mathematical analysis of this phenomenon is, to the best
of our knowledge, presented here for the first time.


title:
Scaling transformation and probability distributions for financial time
  series

abstract:
  The price of financial assets are, since Bachelier, considered to be
described by a (discrete or continuous) time sequence of random variables, i.e
a stochastic process. Sharp scaling exponents or unifractal behavior of such
processes has been reported in several works. In this letter we investigate the
question of scaling transformation of price processes by establishing a new
connexion between non-linear group theoretical methods and multifractal methods
developed in mathematical physics. Using two sets of financial chronological
time series, we show that the scaling transformation is a non-linear group
action on the moments of the price increments. Its linear part has a spectral
decomposition that puts in evidence a multifractal behavior of the price
increments.


title:
Interlayer Conductivity in the Superconductor Tl-Ba-Cu-O: Energetics and
  Energy Scales

abstract:
  We report on infrared studies of the c-axis electrodynamics of Tl-Ba-Cu-O
(Tl-2201) crystals. A sum rule analysis reveals spectral weight shifts that can
be interpreted as a kinetic energy change at the superconducting transistion.
In optimally doped crystals, showing an incoherent normal state response, the
kinetic energy is lowered at T < Tc, but no significant change is found in the
over-doped samples, which have more coherent conductivity at T > Tc.


title: Phonon-mediated thermal conductance of mesoscopic wires with rough edges

abstract:
  We present an analysis of acoustic phonon propagation through long,
free-standing, insulating wires with rough surfaces. Due to a crossover from
ballistic propagation of the lowest-frequency phonon mode at $\omega <\omega
_{1}=\pi c/W$ to a diffusive (or even localized) behavior upon the increase of
phonon frequency, followed by re-entrance into the quasi-ballistic regime, the
heat conductance of a wire acquires an intermediate tendency to saturate within
the temperature range $T\sim \hbar \omega_{1}/k_{B}$.


title: Stripes, Carriers, and High Tc in the Cuprates

abstract:
  Considering both "large-U" and "small-U" orbitals it is found that the
high-Tc cuprates are characterized by a striped structure, and three types of
carriers: polaron-like "stripons" carrying charge, "quasielectrons" carrying
charge and spin, and "svivons" carrying spin and lattice distortion. It is
shown that this electronic structure leads to the anomalous physical properties
of the cuprates, and specifically the systematic behavior of the resistivity,
Hall constant, and thermoelectric power. High-Tc pairing results from
transitions between pair states of quasielectrons and stripons through the
exchange of svivons. A pseudogap phase occurs when pairing takes place above
the temperature where stripons become coherent, and this temperature determines
the Uemura limit.


title: Velocity Distributions & Density Fluctuations in a 2D Granular Gas

abstract:
  Velocity distributions in a vibrated granular monolayer are investigated
experimentally. Non-Gaussian velocity distributions are observed at low
vibration amplitudes but cross over smoothly to Gaussian distributions as the
amplitude is increased. Cross-correlations between fluctuations in density and
temperature are present only when the velocity distributions are strongly
non-Gaussian. Confining the expansion of the granular layer results in
non-Gaussian velocity distributions that persist to high vibration amplitudes.


title:
Electron-Phonon Correlations, Polaron Size, and the Nature of the
  Self-Trapping Transition

abstract:
  We analyze electron-phonon correlation functions measured in 1D polaron
ground states of the Holstein Hamiltonian using the Global-Local variational
method. The spatial collapse of electron-phonon correlations is found to occur
in concert with transition behavior in other polaron properties, providing
mutually confirming evidence for a self-trapping line in 1D. The spatial extent
of electron-phonon correlations is used to quantify polaron size, and is
analyzed over a wide range of parameters. Distinct scaling behaviors are found
to be characteristic of the region below the self-trapping transition and above
it, contrary to some widely-held expectations and leading naturally to the
notion of the polaron size as an order parameter for a self-trapping transition
that becomes critical in the adiabatic limit.


title:
Application of Raman Scattering to Study the Strain Distribution in SiGe
  Layers

abstract:
  In this paper, we mainly present a new simple, efficient and nondestructive
Raman scattering analysis method to study the distribution of strain in SiGe
alloy films. The method can simultaneously determine both Ge fractional
composition x and strain of SiGe films. We use the Ar+ laser lines (514.5, 488
and 457.9 nm) to detect the information of different depth of SiGe layers. The
results show that the x value (about 0.50) of Si1-xGex and the strain of the
films decrease from the interface between SiGe layers and Si substrates to SiGe
surface.


title:
Nonmonotonic Temperature-dependent Resistance in Low Density 2D Hole
  Gases

abstract:
  The low temperature longitudinal resistance-per-square Rxx(T) in ungated
GaAs/AlGaAs quantum wells of high peak hole mobility 1.7x10^6 cm^2/Vs is
metallic for 2D hole density p as low as 3.8x10^9 cm-2. The electronic
contribution to the resistance, R_{el}(T), is a nonmonotonic function of T,
exhibiting thermal activation, R_{el}(T) ~ exp{-E_a/kT}, for kT<<E_F and a
heretofore unnoted decay R_{el}(T) ~ 1/T for k_T>EF. The form of R_{el}(T) is
independent of density, indicating a fundamental relationship between the low
and high T scattering mechanisms in the metallic state.


title:
Wave Scattering through Classically Chaotic Cavities in the Presence of
  Absorption: An Information-Theoretic Model

abstract:
  We propose an information-theoretic model for the transport of waves through
a chaotic cavity in the presence of absorption. The entropy of the S-matrix
statistical distribution is maximized, with the constraint $<Tr SS^{\dagger}>
=\alpha n$: n is the dimensionality of S, and $0\leq \alpha \leq 1, \alpha
=0(1)$ meaning complete (no) absorption. For strong absorption our result
agrees with a number of analytical calculations already given in the
literature. In that limit, the distribution of the individual (angular)
transmission and reflection coefficients becomes exponential -Rayleigh
statistics- even for n=1. For $n\gg 1$ Rayleigh statistics is attained even
with no absorption; here we extend the study to $\alpha <1$. The model is
compared with random-matrix-theory numerical simulations: it describes the
problem very well for strong absorption, but fails for moderate and weak
absorptions. Thus, in the latter regime, some important physical constraint is
missing in the construction of the model.


title: Rodrigues Formula for the Nonsymmetric Multivariable Hermite Polynomial

abstract:
  Applying a method developed by Takamura and Takano for the nonsymmetric Jack
polynomial, we present the Rodrigues formula for the nonsymmetric multivariable
Hermite polynomial.

categories: cond-mat.stat-mech hep-th nlin.SI solv-int


title: Rodrigues Formula for the Nonsymmetric Multivariable Laguerre Polynomial

abstract:
  Extending a method developed by Takamura and Takano, we present the Rodrigues
formula for the nonsymmetric multivariable Laguerre polynomials which form the
orthogonal basis for the $B_{N}$-type Calogero model with distinguishable
particles. Our construction makes it possible for the first time to
algebraically generate all the nonsymmetric multivariable Laguerre polynomials
with different parities for each variable.


title:
Quasiparticle spectrum of a type-II superconductor in a high magnetic
  field with randomly pinned vortices

abstract:
  We show that gapless superconductivity of a strongly type-II superconductor
in a high magnetic field prevails in the presence of disorder, suggesting a
topological nature. We calculate the density of states of the Bogoliubov-de
Gennes quasiparticles for a two-dimensional inhomogeneous system in both cases
of weak and strong disorder. In the limit of very weak disorder, the effect is
very small and the density of states is not appreciably changed. As the
disorder increases, the density of states at low energies increases and the
ratio of the low-energy density of states to its maximum increases
significantly.


title: Hall conductance of a pinned vortex lattice in a high magnetic field

abstract:
  We calculate the quasiparticle contribution to the zero temperature Hall
conductance of two-dimensional extreme type-II superconductors in a high
magnetic field, using the Landau basis. As one enters the superconducting phase
the Hall conductance is renormalized to smaller values, with respect to the
normal state result, until a quantum level-crossing transition is reached. At
high values of the order parameter, where the quasiparticles are bound to the
vortex cores, the Hall conductance is expected to tend to zero due to a theorem
of Thouless.


title: Spin domain formation in spinor Bose-Einstein condensation

abstract:
  The spatial structure of the spinor Bose-Einstein condensates with the spin
degrees of freedom is analyzed based on the generalized Gross-Pitaevskii
equation (GP) in the light of the present spin domain experiment on m_F=\pm 1,
and 0 of the hyperfine state F=1 of ^{23}Na atom gases. The GP solutions in
three- and one-spatial dimensional cases reproduce the observed spin domain
structures, revealing the length scale associated with the existence of the
weak interaction of the spin-spin channel, other than the ordinary coherence
length related to the density-density channel. The obtained domain structure in
GP is compared with the result in Thomas-Fermi approximation. The former
solution is found to better describe the observed features than the latter.


title:
Simulation of a Single Polymer Chain in Solution by Combining Lattice
  Boltzmann and Molecular Dynamics

abstract:
  In this paper we establish a new efficient method for simulating
polymer-solvent systems which combines a lattice Boltzmann approach for the
fluid with a continuum molecular dynamics (MD) model for the polymer chain. The
two parts are coupled by a simple dissipative force while the system is driven
by stochastic forces added to both the fluid and the polymer. Extensive tests
of the new method for the case of a single polymer chain in a solvent are
performed. The dynamic and static scaling properties predicted by analytical
theory are validated. In this context, the influence of the finite size of the
simulation box is discussed. While usually the finite size corrections scale as
L^{-1} (L denoting the linear dimension of the box), the decay rate of the
Rouse modes is only subject to an L^{-3} finite size effect. Furthermore, the
mapping to an existing MD simulation of the same system is done so that all
physical input values for the new method can be derived from pure MD
simulation. Both methods can thus be compared quantitatively, showing that the
new method allows for much larger time steps. Comparison of the results for
both methods indicates systematic deviations due to non-perfect match of the
static chain conformations.


title: An integration scheme for reaction-diffusion models

abstract:
  A detailed description and validation of a recently developed integration
scheme is here reported for one- and two-dimensional reaction-diffusion models.
As paradigmatic examples of this class of partial differential equations the
complex Ginzburg-Landau and the Fitzhugh-Nagumo equations have been analyzed.
The novel algorithm has precision and stability comparable to those of
pseudo-spectral codes, but it is more convenient to employ for systems with
quite large linear extention $L$. As for finite-difference methods, the
implementation of the present scheme requires only information about the local
enviroment and this allows to treat also system with very complicated boundary
conditions.

categories: cond-mat.stat-mech chao-dyn cond-mat.dis-nn nlin.CD


title: Angle-resolved photoemission in doped charge-transfer Mott insulators

abstract:
  A theory of angle-resolved photoemission (ARPES) in doped cuprates and other
charge-transfer Mott insulators is developed taking into account the realistic
(LDA+U) band structure, (bi)polaron formation due to the strong electron-phonon
interaction, and a random field potential. In most of these materials the first
band to be doped is the oxygen band inside the Mott-Hubbard gap. We derive the
coherent part of the ARPES spectra with the oxygen hole spectral function
calculated in the non-crossing (ladder) approximation and with the exact
spectral function of a one-dimensional hole in a random potential. Some unusual
features of ARPES including the polarisation dependence and spectral shape in
YBa2Cu3O7 and YBa2Cu4O8 are described without any Fermi-surface, large or
small. The theory is compatible with the doping dependence of kinetic and
thermodynamic properties of cuprates as well as with the d-wave symmetry of the
superconducting order parameter.


title: Effects of macroscopic polarization in III-V nitride multi-quantum-wells

abstract:
  Huge built-in electric fields have been predicted to exist in wurtzite III-V
nitrides thin films and multilayers. Such fields originate from heterointerface
discontinuities of the macroscopic bulk polarization of the nitrides. Here we
discuss the background theory, the role of spontaneous polarization in this
context, and the practical implications of built-in polarization fields in
nitride nanostructures. To support our arguments, we present detailed
self-consistent tight-binding simulations of typical nitride QW structures in
which polarization effects are dominant.


title:
Quasi-harmonic vs. ``exact'' surface free energies of Al: a systematic
  study employing a new interatomic potential

abstract:
  We discuss a computationally efficient classical many-body potential designed
to model the Al-Al interaction in a wide range of bonding geometries. We show
that the potential yields results in properties in excellent agreement with
experiment and ab initio results for a number of bulk and surface properties,
among others for surface and step formation energies, and self-diffusion
barriers. As an application, free energy calculations are performed for the Al
(100) surface by Monte Carlo thermodynamic integration and the quasi-harmonic
approximation. Comparison of the latter approximation with the reference Monte
Carlo results provides informations on its range of applicability to surface
problems at high temperatures.


title:
Numerical signs for a transition in the 2d Random Field Ising Model at
  T=0

abstract:
  Intensive numerical studies of exact ground states of the 2-d ferromagnetic
random field Ising model at T=0 with gaussian distribution of fields are
presented. Standard finite size scaling analysis of the data suggests the
existence of a transition at sigma_c= 0.64 +/- 0.08. Results are compared with
existing theories and with the study of metastable avalanches in the same
model.


title: On the origin of ultrametricity

abstract:
  In this paper we show that in systems where the probability distribution of
the the overlap is non trivial in the infinity volume limit, the property of
ultrametricity can be proved in general starting from two very simple and
natural assumptions: each replica is equivalent to the others (replica
equivalence or stochastic stability) and all the mutual information about a
pair of equilibrium configurations is encoded in their mutual distance or
overlap (separability or overlap equivalence).


title: Quantum Phase Pumping

abstract:
  In this Letter, we consider the adiabatic charge transport through a normal
mesoscopic sample sandwiched by superconductors without modulation of local
chemical potentials. The deformation of coherent quasiparticles in the normal
metal in the presence of periodically changing phases in the superconductors
leads to a charge transport. Both the magnitude and the phase dependence of the
charge transferred per period through the sample strongly depend on
temperature.


title: The Largest Cluster in Subcritical Percolation

abstract:
  The statistical behavior of the size (or mass) of the largest cluster in
subcritical percolation on a finite lattice of size $N$ is investigated (below
the upper critical dimension, presumably $d_c=6$). It is argued that as $N \to
\infty$ the cumulative distribution function converges to the Fisher-Tippett
(or Gumbel) distribution $e^{-e^{-z}}$ in a certain weak sense (when suitably
normalized). The mean grows like $s_\xi^* \log N$, where $s_\xi^*(p)$ is a
``crossover size''. The standard deviation is bounded near $s_\xi^*
\pi/\sqrt{6}$ with persistent fluctuations due to discreteness. These
predictions are verified by Monte Carlo simulations on $d=2$ square lattices of
up to 30 million sites, which also reveal finite-size scaling. The results are
explained in terms of a flow in the space of probability distributions as $N
\to \infty$. The subcritical segment of the physical manifold ($0 < p < p_c$)
approaches a line of limit cycles where the flow is approximately described by
a ``renormalization group'' from the classical theory of extreme order
statistics.

categories: cond-mat.stat-mech math-ph math.MP math.PR


title:
Non-Abelian fractional quantum Hall states and chiral coset conformal
  field theories

abstract:
  We propose an effective Lagrangian for the low energy theory of the Pfaffian
states of the fractional quantum Hall effect in the bulk in terms of
non-Abelian Chern-Simons (CS) actions. Our approach exploits the connection
between the topological Chern-Simons theory and chiral conformal field
theories. This construction can be used to describe a large class of
non-Abelian FQH states.


title: Properties of two - dimensional dusty plasma clusters

abstract:
  Two-dimensional classical cluster of particles interacting through a screened
Coulomb potential is studied. This system can be used as a model for "dusty
particles" in high-frequency discharge plasma. For systems consisting of N = 2
- 40 particles and confined by a harmonic potential we find ground-state
configurations, eigenfrequencies and eigenvectors for the normal modes as a
function of the Debye screening length R_D in plasma. Variations in R_D cause
changes in the ground-state structure of clusters, each structural
rearrangement can be considered as a phase transition of first or second order
(with respect to parameter R_D). Monte Carlo and molecular dynamics are used to
study in detail the melting of the clusters as the temperature is increased. By
varying the density and the temperature of plasma, to which the particles are
immersed, one can modulate thermodynamical properties of the system,
transforming it in a controllable way to an ordered (crystal-like),
orientationaly disordered or totally disordered (liquid-like) states. The
possibility of dynamical coexistence phenomena in small clusters is discussed.


title: Quantum orientational melting of mesoscopic clusters

abstract:
  By path integral Monte Carlo simulations we study the phase diagram of two -
dimensional mesoscopic clusters formed by electrons in a semiconductor quantum
dot or by indirect magnetoexcitons in double quantum dots. At zero (or
sufficiently small) temperature, as quantum fluctuations of particles increase,
two types of quantum disordering phenomena take place: first, at small values
of quantum de Boer parameter q < 0.01 one can observe a transition from a
completely ordered state to that in which different shells of the cluster,
being internally ordered, are orientationally disordered relative to each
other. At much greater strengths of quantum fluctuations, at q=0.1, the
transition to a disordered (superfluid for the boson system) state takes place.


title:
Introduction to the Propp-Wilson Method of Exact Sampling for the Ising
  Model

abstract:
  An introduction to the Propp-Wilson method of coupling-from-the-past for the
Ising model is presented. It enables one to obtain exact samples from the
equilibrium spin distribution for ferromagnetic interactions. Both uniform and
random quenched magnetic fields are included. The time to couple from the past
and its standard deviation are shown as functions of system size, temperature,
and the field strength. The time should be an estimate of the ergodic time for
the Ising system.


title:
Application of Ultraviolet Fluorescence in Wafer Surface Cleaning
  Analysis

abstract:
  Ultraviolet fluorescence (UVF) is introduced as a novel and versatile method
for the determination of the contamination of metal impurities on silicon wafer
surfaces. The results given demonstrate the usefulness of UVF for contamination
control in silicon wafer processing. The experiments show some main
characteristic peaks such as Fe, Cu, Ni and Na at room temperature. Compared
with other surface sensitive techniques, the main advantages of UVF are low
detection limits, simultaneous multi-element analysis and high sensitivity (up
to 109 Fe/cm2).


title: Ab initio molecular dynamics simulations of Aluminum solvation

abstract:
  The solvation of Al and its hydrolyzed species in water clusters has been
studied by means of ab initio molecular dynamics simulations. The hexa-hydrate
aluminum ion formed a stable complex in the finite temperature cluster
simulation of one aluminum ion and 16 waters. The average dipole moment of
strongly polarized hydrated water molecules in the first solvation shell of the
hexa-hydrate aluminum ion was found to be 5.02 Debye. The deprotonated
hexa-hydrate complex evolves into a tetra-coordinated aluminate ion with two
water molecules in the second solvation shell forming hydrogen bonds to the
hydroxyl groups in agreement with the observed coordination.


title: Transition Temperature of the homogeneous, weakly interacting Bose gas

abstract:
  We present a Monte Carlo calculation for up to $N \sim 20 000$ bosons in 3 D
to determine the shift of the transition temperature due to small interactions
$a$. We generate independent configurations of the ideal gas. At finite $N$,
the superfluid density changes by a certain correlation function in the limit
$a \to 0$; the $N \to \infty$ limit is taken afterwards. We argue that our
result is independent of the order of limits. Detailed knowledge of the
non-interacting system for finite $N$ allows us to avoid finite-size scaling
assumptions.


title:
Equivalence of the two results for the free energy of the chiral Potts
  model

abstract:
  The free energy of the chiral Potts model has been obtained in two ways. The
first used only the star-triangle relation, symmetries and invariances, and led
to a system of equations that implicitly define the free energy, and from which
the critical behaviour can be obtained. The second used the functional
relations derived by Bazhanov and Stroganov, solving them to obtain the free
energy explicitly as a double integral. Here we obtain, for the first time, a
direct verification that the two results are identical at all temperatures.


title:
Dynamics of the Measurement of Nuclear Spins in a Solid-State Quantum
  Computer

abstract:
  We study numerically the process of nuclear spin measurement in a solid-state
quantum computer of the type proposed by Kane by modeling the quantum dynamics
of two coupled nuclear spins on $^{31}$P donors implanted in silicon. We
estimate the minimum measurement time necessary for the reliable transfer of
quantum information from the nuclear spin subsystem to the electronic
subsystem. We also calculate the probability of error for typical values of the
external noise.


title:
Universal scaling of Hall resistivity in clean and moderately clean
  limits for Hg- and Tl-based superconductors

abstract:
  The mixed-state Hall resistivity and the longitudinal resistivity in
HgBa_{2}CaCu_{2}O_{6}, HgBa_{2}Ca_{2}Cu_{3}O_{8}, and Tl_{2}Ba_{2}CaCu_{2}O_{8}
thin films have been investigated as functions of the magnetic field up to 18
T. We observe the universal scaling behavior between \rho_{xy} and \rho_{xx} in
the regions of the clean and the moderately clean limit. The scaling exponent
\beta is 1.9 in the clean limit at high field and low temperature whereas \beta
is 1.0 in the moderately clean limit at low field and high temperature,
consistent with a theory based on the midgap states in the vortex cores. This
finding implies that the Hall conductivity is also universal in Hg- and
Tl-based superconductors.


title:
Scaling and finte-size-scaling in the two dimensional random-coupling
  Ising ferromagnet

abstract:
  It is shown by Monte Carlo method that the finite size scaling (FSS) holds in
the two dimensional random-coupled Ising ferromagnet. It is also demonstrated
that the form of universal FSS function constructed via novel FSS scheme
depends on the strength of the random coupling for strongly disordered cases.
Monte Carlo measurements of thermodynamic (infinite volume limit) data of the
correlation length ($\xi$) up to $\xi \simeq 200$ along with measurements of
the fourth order cumulant ratio (Binder's ratio) at criticality are reported
and analyzed in view of two competing scenarios. It is demonstrated that the
data are almost exclusively consistent with the scenario of weak universality.


title:
Geometry, thermodynamics, and finite-size corrections in the critical
  Potts model

abstract:
  We establish an intriguing connection between geometry and thermodynamics in
the critical q-state Potts model on two-dimensional lattices, using the q-state
bond-correlated percolation model (QBCPM) representation. We find that the
number of clusters of the QBCPM has an energy-like singularity for q different
from 1, which is reached and supported by exact results, numerical simulation,
and scaling arguments. We also establish that the finite-size correction to the
number of bonds, has no constant term and explains the divergence of related
quantities as q --> 4, the multicritical point. Similar analyses are applicable
to a variety of other systems.


title:
Magnetic hysteresis in the Cu-Al-Mn intermetallic alloy: experiments and
  modeling

abstract:
  We study isothermal magnetization processes in the Cu-Al-Mn intermetallic
alloy. Hysteresis is observed at temperatures below the spin-freezing of the
system. The characteristics of the hysteresis cycles as a function of
temperature and Mn content (magnetic element) are obtained. At low temperature
(5 K) a change from smooth to sharp cycles is observed with increasing Mn
content, which is related to the decrease of configurational disorder. We also
study a zero-temperature site-diluted Ising model, suitable for the description
of this Cu-Al-Mn system. The model reproduces the main features of the
hysteresis loops observed experimentally. It exhibits a disorder-induced
critical line separating a disordered phase from an incipient ferromagnetic
ground-state. The comparison between the model and the experiments allows to
conclude that the observed change in the experimental hysteresis loops can be
understood within the framework of the theory of disorder-induced criticality
in fluctuationless first-order phase transitions.


title: The Influence of Substrate Structure on Membrane Adhesion

abstract:
  We consider a membrane both weakly and strongly adhering to a geometrically
structured substrate. The interaction potential is assumed to be local, via the
Deryagin approximation, and harmonic. Consequently, we can analytically
describe a variety of different geometries: as well as randomly rough
self-affine surfaces, smooth substrates interrupted by an isolated cylindrical
pit, a single elongated trench or a periodic array of trenches are
investigated. We present more general expressions for the adhesion energy and
membrane configuration in Fourier space and find that, compared to planar
surfaces, the adhesion energy decreases. We also highlight the possibility of
overshoots occurring in the membrane profile and look at its degree of
penetration into surface indentations.


title: The Phase Diagram of Star Polymer Solutions

abstract:
  The phase diagram of star polymer solutions in a good solvent is obtained
over a wide range of densities and arm numbers by Monte Carlo simulations. The
effective interaction between the stars is modeled by an ultrasoft pair
potential which is logarithmic in the core-core distance. Among the stable
phases are a fluid as well as body-centered cubic, face-centered cubic,
body-centered orthogonal, and diamond crystals. In a limited range of arm
numbers, reentrant melting and reentrant freezing transitions occur for
increasing density.


title: The inverse Mermin-Wagner theorem for classical spin models on graphs

abstract:
  In this letter we present the inversion of the Mermin-Wagner theorem on
graphs, by proving the existence of spontaneous magnetization at finite
temperature for classical spin models on transient on the average (TOA) graphs,
i.e. graphs where a random walker returns to its starting point with an average
probability $\bar F < 1$. This result, which is here proven for models with
O(n) symmetry, includes as a particular case $n=1$, providing a very general
condition for spontaneous symmetry breaking on inhomogeneous structures even
for the Ising model.


title:
Decay properties of the density matrix and Wannier functions for
  interacting systems

abstract:
  For non-interacting electrons the one-particle density matrix and the related
Wannier functions characterize a material as insulating or metallic.
Introducing many-body Wannier functions, we show that this characterization can
be carried over to interacting systems. In particular, we find that an
exponential decay of the density matrix characterizes not only band insulators
but also Mott insulators. The properties of the many-body Wannier functions
differ, however, from those of the Wannier functions of a non-interacting
systems.


title: Magnetic Domain Walls in Double Exchange Materials

abstract:
  We study magnetic domain walls in double exchange materials. The domain wall
width is proportional to the square root of the stiffness. In the double
exchange model the stiffness has two terms: the kinetic energy and the Hartree
term. The kinetic energy term comes from the decrease of the tunneling
amplitude in the domain wall region. The Hartree term appears only in double
exchange materials and it comes from the connection between band-width and
magnetization. We also calculate the low-field magnetoresistance associated
with the existence of magnetic domains. We find a magnetoresistance of 1-2%.
The magnetoresistance c an be considerably larger in magnetically constrained
nanocontacts.


title:
Phase-coherent tunneling through mesoscopic superconductor coupled with
  superconducting and normal metal electrodes

abstract:
  Phase-coherent diffusive transport through mesoscopic hybrid
superconductor/normal metal tunneling structures is investigated. For a N-s-S
two-barrier tunneling system with bulk S and N electrodes coupled by a
mesoscopic superconducting constriction s, zero-bias conductance and non-linear
I-V curves are calculated under the assumption that the dwell times of
quasiparticles in the s region is shorter than inelastic relaxation time. It is
shown that the low voltage conductance of this system determined by the Andreev
reflection processes may exceed the conductance in the normal state and its
value is very sensitive to the weak pairing interaction of electrons in the s
region. We show that even weak pairing electron interaction may result in the
significant qualitative and quantitative change of the conductance temperature
dependence with respect to the case of structures with the normal mesoscopic
region. We calculate the I-V curves and show that they depend on the applied
voltage in a non-monotonic way, therefore differential conductance becomes
negative with increasing voltage. Such behavior is due to the voltage
dependence of the order parameter in the constriction and the phase difference,
phi, between the S and s superconductors. It is shown that if the tunneling
processes determine the form of the quasiparticle distribution function in the
s superconductor, the phase, phi, is stationary at arbitrary voltages. For
quasiparticle tunneling interferometers in which the mesoscopic
superconductor,s, couples the superconductor,S, and the normal metal,N, the
zero bias conductance, as a function of the phase difference between the S
electrodes is investigated. It is shown that the amplitude of the conductance
oscillations may exceed the conductance of this structure in the normal state.


title:
Crossover Phenomena in the One-Dimensional SU(4) Spin-Orbit Model under
  Magnetic Fields

abstract:
  We study the one-dimensional SU(4) exchange model under magnetic fields,
which is the simplest effective Hamiltonian in order to investigate the quantum
fluctuations concerned with the orbital degrees of freedom in coupled
spin-orbit systems. The Bethe ansatz approaches and numerical calculations
using the density matrix renormalization group method are employed. The main
concern of the paper is how the system changes from the SU(4) to the SU(2)
symmetric limit as the magnetic field is increased. For this model the
conformal field theory predicts an usual behavior: there is a jump of the
critical exponents just before the SU(2) limit. For a finite-size system,
however, the orbital-orbital correlation functions approach continuously to the
SU(2) limit after interesting crossover phenomena. The crossover takes place in
the magnetization range of 1/3 $\sim$ 1/2 for the system with 72 sites studied
in this paper.


title:
Critical behavior of roughening transitions in parity-conserving growth
  processes

abstract:
  We investigate a class of parity-conserving solid-on-solid models which
describe the growth of an interface by the deposition and evaporation of
dimers. As a key feature of the models, evaporation of dimers takes place only
at the edges of terraces, leading to a roughening transition between a smooth
and a rough phase. We consider several variants of growth models in order to
identify universal and nonuniversal properties. Moreover, a parity-conserving
polynuclear growth model is proposed. All variants display the same type of
universal critical behavior at the roughening transition. Because of
parity-conservation, the critical behavior at the first few layers can be
explained in terms of unidirectionally coupled branching annihilating random
walks with even number of offspring.


title: Is there an Optimal Substrate Geometry for Wetting ?

abstract:
  We consider the problem of the Winterbottom's construction and Young's
equation in the presence of a rough substate and establish their microscopic
validity within a 1+1-dimensional SOS type model. We then present the low
temperature expansion of the wall tension leading to the Wenzel's law for the
wall tension and its corrections. Finally, for a fix roughness, we compare the
influence of different geometries of the substrate on wetting properties. We
show that there is an optimal geometry with a given roughness for a certain
class of simple substrates. Our results are in agreement and explain recent
numerical simulations.


title: String Picture of Bose-Einstein Condensation

abstract:
  A nonrelativistic Bose gas is represented as a grand-canonical ensemble of
fluctuating closed spacetime strings of arbitrary shape and length. The loops
are characterized by their string tension and the number of times they wind
around the imaginary time axis. At the temperature where Bose-Einstein
condensation sets in, the string tension, being determined by the chemical
potential, vanishes, the system becomes critical, and the strings proliferate.
A comparison with Feynman's description in terms of rings of cyclicly permuted
bosons shows that the winding number of a loop corresponds to the number of
particles contained in a ring.


title:
Monte Carlo Renormalization Group Analysis of Lattice $\phi^4$ Model in
  $D=3,4$

abstract:
  We present a simple, sophisticated method to capture renormalization group
flow in Monte Carlo simulation, which provides important information of
critical phenomena. We applied the method to $D=3,4$ lattice $\phi^4$ model and
obtained renormalization flow diagram which well reproduces theoretically
predicted behavior of continuum $\phi^4$ model. We also show that the method
can be easily applied to much more complicated models, such as frustrated spin
models.