title: Luttinger-liquid-like transport in long InSb nanowires

abstract:
  Long nanowires of degenerate semiconductor InSb in asbestos matrix (wire
diameter is around 50 \AA, length 0.1 - 1 mm) were prepared. Electrical
conduction of these nanowires is studied over a temperature range 1.5 - 350 K.
It is found that a zero-field electrical conduction is a power function of the
temperature $G\propto T^\alpha$ with the typical exponent $\alpha \approx 4$.
Current-voltage characteristics of such nanowires are found to be nonlinear and
at sufficiently low temperatures follows the power law $I\propto V^\beta$. It
is shown that the electrical conduction of these nanowires cannot be accounted
for in terms of ordinary single-electron theories and exhibits features
expected for impure Luttinger liquid. For a simple approximation of impure LL
as a pure one broken into drops by weak links, the estimated weak-link density
is around $10^3-10^4$ per cm.


title: New Boundary Bound States in an Open Quantum Spin Chain

abstract:
  New boundary bound states (BBS) are found of an integrable model with the
magnetic impurities located at the edges of an open Heisenberg spin chain.
These bound states carry the real energy and are formed by three or five
imaginary modes of the rapidities. These imaginary modes of the rapidities give
the non-zero antisymmetric wave functions and the moments of the centers of the
bound states are zero. It means that these bound states are arisen by the
magnetic impurities and localized at the edges of the correlated system. The
Kondo screening occurs for the antiferromagnetic spin chain with the
ferromagnetic impurities-electrons exchange interaction.


title: Two Magnetic Impurities with Arbitrary Spins in Open Boundary t-J Model

abstract:
  From the open boundary t-J model, an impurity model is constructed in which
magnetic impurities of arbitrary spins are coupled to the edges of the strongly
correlated electron system. The boundary R matrices are given explicitly. The
interaction parameters between magnetic impurities and electrons are related to
the potentials of the impurities to preserve the integrability of the system.
The Hamiltonian of the impurity model is diagonalized exactly. The integral
equations of the ground state are derived and the ground state properties are
discussed in details. We discuss also the string solutions of the Bethe ansatz
equations, which describe the bound states of the charges and spins. By
minimizing the thermodynamic potential we get the thermodynamic Bethe ansatz
equations. The finite size correction of the free energy contributed by the
magnetic impurities is obtained explicitly. The properties of the system at
some special limits are discussed and the boundary bound states are obtained.


title:
Two Experimental Tests of the Halperin-Lubensky-Ma Effect at the
  Nematic-Smectic-A Phase Transition

abstract:
  We have conducted two quantitative tests of predictions based on the
Halperin-Lubensky-Ma (HLM) theory of fluctuation-induced first-order phase
transitions. First, we explore the effect of an external magnetic field on the
nematic-smectic-A (NA) transition in a liquid crystal. Second, we examine the
dependence of the first-order discontinuity as a function of mixture
concentration in pure 8CB and three 8CB-10CB mixtures. We find the first
quantitative evidence for deviations from the HLM theory.


title: Chiral Glass Phase in Ceramic Superconductors

abstract:
  A three-dimensional lattice of the Josephson junctions with a finite
self-conductance is employed to model the ceramic superconductors. By Monte
Carlo simulations it is shown that the chiral glass phase is stable in three
dimensions even under the influence of screening. The nonlinear ac
susceptibility and the compensation effect are also studied. The compensation
effect is shown to be due to the existence of the chiral glass phase. In
agreement with experiments, this effect is demonstrated to be present in the
ceramic superconductors which show the paramagnetic Meissner effect.


title:
The interplay between flattening and damping of single particle spectra
  in strongly correlated Fermi systems

abstract:
  The self-consistent theory of the fermion condensation, a specific phase
transition which results in a rearrangement of the single particle degrees of
freedom in strongly correlated Fermi systems is developed. Beyond the phase
transition point, the single particle spectra are shown to be flat. The
interplay between the flattening and the damping of the single particle spectra
at $T\to 0$ is investigated. The width $\gamma(\epsilon)$ of the single
particle states is found to grow up linearly with $\epsilon$ over a wide range
of energy as in a marginal Fermi liquid. Our results gain insight into the
success of the phenomenological theory of the normal states of high-temperature
superconductors by Varma et al.


title:
Anomalous behavior of the irreversible magnetization and time relaxation
  in YBa$_2$Cu$_3$O$_7$ single crystals with splayed tracks

abstract:
  We have studied the angular dependence of the irreversible magnetization and
its time relaxation in YBa$_2$Cu$_3$O$_7$ single crystals with one or two
families of columnar defects inclined with respect to the c-axis. At high
magnetic fields, the magnetization shows the usual maximum centered at the mean
tracks' orientation and an associated minimum in the normalized relaxation
rate. In contrast, at low fields we observe an anomalous local minimum in the
magnetization and a maximum in the relaxation rate. We present a model to
explain this anomaly based on the slowing down of the creep processes arising
from the increase of the vortex-vortex interactions as the applied field is
tilted away from the mean tracks' direction.


title:
Theoretical Model for the Kramers-Moyal Description of Turbulence
  Cascades

abstract:
  We derive the Kramers-Moyal equation for the conditional probability density
of velocity increments from the theoretical model recently proposed by V.Yakhot
[Phys.Rev.E {\bf 57}, 1737 (1998)] in the limit of high Reynolds number limit.
We show that the higher order (n>=3) Kramers-Moyal coefficients tends to zero
and the velocity increments are evolved by the Fokker-Planck operator. Our
result is compatible with the phenomenological descriptions by R.Friedrich and
J.Peinke [Phys.Rev.Lett. {\bf 78}, 863 (1997)].


title: Developing the MTO Formalism

abstract:
  We review the simple linear muffin-tin orbital method in the atomic-spheres
approximation and a tight-binding representation (TB-LMTO-ASA method), and show
how it can be generalized to an accurate and robust Nth order muffin-tin
orbital (NMTO) method without increasing the size of the basis set and without
complicating the formalism. On the contrary, downfolding is now more efficient
and the formalism is simpler and closer to that of screened multiple-scattering
theory. The NMTO method allows one to solve the single-electron Schroedinger
equation for a MT-potential -in which the MT-wells may overlap- using basis
sets which are arbitrarily minimal. The substantial increase in accuracy over
the LMTO-ASA method is achieved by substitution of the energy-dependent partial
waves by so-called kinked partial waves, which have tails attached to them, and
by using these kinked partial waves at N+1 arbitrary energies to construct the
set of NMTOs. For N=1 and the two energies chosen infinitesimally close, the
NMTOs are simply the 3rd-generation LMTOs. Increasing N, widens the energy
window, inside which accurate results are obtained, and increases the range of
the orbitals, but it does not increase the size of the basis set and therefore
does not change the number of bands obtained. The price for reducing the size
of the basis set through downfolding, is a reduction in the number of bands
accounted for and -unless N is increased- a narrowing of the energy window
inside which these bands are accurate. A method for obtaining orthonormal NMTO
sets is given and several applications are presented.


title: Multi-scale Correlation Functions in Strong Turbulence

abstract:
  Under the framework of V. Yakhot [Phys.Rev.E, {\bf57}, 1737 (1998)] modelling
of intermittent structure functions in fully developed turbulence and based on
the experimentally supported Markovian nature of turbulence cascades
[R.Friedrich and J.Peinke, Phys.Rev.Lett, {\bf 78}, 863 (1997)], we calculate
the multiscaling correlation functions. Fusion rules [V.S.L'vov and I.
Procaccia, Phys.Rev.Lett. {\bf 76}, 2898 (1996)] which are experimentally
tested [R. Benzi, L. Biferale, and F. Toschi, Phys.Rev.Lett. {\bf 80}, 3244
(1998)] to be compatible with almost uncorrelated multiplicative process can
analyticaly be supported by direct calculations.


title:
Systematic Two-band Model Calculations of the GMR Effect with Metallic
  and Nonmetallic Spacers and with Impurities

abstract:
  By an accurate Green's function method we calculate conductances and the
corresponding Giant Magneto-Resistance effects (GMR) of two metallic
ferromagnetic films separated by different spacers, metallic and non-metallic
ones, in a simplified model on a sc lattice, in CPP and CIP geometries (i.e.
current perpendicular or parallel to the planes), without impurities, or with
interface- or bulk impurities. The electronic structure of the systems is
approximated by two hybridized orbitals per atom, to mimic s-bands and d-bands
and their hybridization.
  We show that such calculations usually give rough estimates only, but of the
correct order of magnitude; in particular, the predictions on the impurity
effects depend strongly on the model parameters. One of our main results is the
prediction of huge CPP-GMR effects for {\it non-metallic} spacers in the
ballistic limit.


title: Distribution of fractal dimensions at the Anderson transition

abstract:
  We investigated numerically the distribution of participation numbers in the
3d Anderson tight-binding model at the localization-delocalization threshold.
These numbers in {\em one} disordered system experience strong level-to-level
fluctuations in a wide energy range. The fluctuations grow substantially with
increasing size of the system. We argue that the fluctuations of the
correlation dimension, $D_2$ of the wave functions are the main reason for
this. The distribution of these correlation dimensions at the transition is
calculated. In the thermodynamic limit ($L\to \infty$) it does not depend on
the system size $L$. An interesting feature of this limiting distribution is
that it vanishes exactly at $D_{\rm 2max}=1.83$, the highest possible value of
the correlation dimension at the Anderson threshold in this model.


title: Mean-field theory for scale-free random networks

abstract:
  Random networks with complex topology are common in Nature, describing
systems as diverse as the world wide web or social and business networks.
Recently, it has been demonstrated that most large networks for which
topological information is available display scale-free features. Here we study
the scaling properties of the recently introduced scale-free model, that can
account for the observed power-law distribution of the connectivities. We
develop a mean-field method to predict the growth dynamics of the individual
vertices, and use this to calculate analytically the connectivity distribution
and the scaling exponents. The mean-field method can be used to address the
properties of two variants of the scale-free model, that do not display
power-law scaling.

categories: cond-mat.dis-nn adap-org cond-mat.stat-mech math-ph math.MP math.PR nlin.AO


title:
Boundary Spatiotemporal Correlations in a Self-Organized Critical Model
  of Punctuated Equilibrium

abstract:
  In a semi-infinite geometry, a 1D, M-component model of biological evolution
realizes microscopically an inhomogeneous branching process for $M \to \infty$.
This implies in particular a size distribution exponent $\tau'=7/4$ for
avalanches starting at a free end of the evolutionary chain. A bulk--like
behavior with $\tau'=3/2$ is restored if `conservative' boundary conditions
strictly fix to its critical, bulk value the average number of species directly
involved in an evolutionary avalanche by the mutating species located at the
chain end. A two-site correlation function exponent ${\tau_R}'=4$ is also
calculated exactly in the `dissipative' case, when one of the points is at the
border. These results, together with accurate numerical determinations of the
time recurrence exponent $\tau_{first}'$, show also that, no matter whether
dissipation is present or not, boundary avalanches have the same space and time
fractal dimensions as in the bulk, and their distribution exponents obey the
basic scaling laws holding there.


title: Two-scale localization in disordered wires in a magnetic field

abstract:
  Calculating the density-density correlation function for disordered wires, we
study localization properties of wave functions in a magnetic field. The
supersymmetry technique combined with the transfer matrix method is used. It is
demonstrated that at arbitrarily weak magnetic field the far tail of the wave
functions decays with the length $L_{{\rm cu}}=2L_{{\rm co}}$, where $L_{{\rm
co}}$ and $L_{{\rm cu}}$ are the localization lengths in the absence of a
magnetic field and in a strong magnetic field, respectively. At shorter
distances, the decay of the wave functions is characterized by the length
$L_{{\rm co}}$. Increasing the magnetic field broadens the region of the decay
with the length $L_{{\rm cu}}$, leading finally to the decay with $L_{{\rm
cu}}$ at all distances. In other words, the crossover between the orthogonal
and unitary ensembles in disordered wires is characterized by two localization
lengths. This peculiar behavior must result in two different temperature
regimes in the hopping conductivity with the boundary between them depending on
the magnetic field.


title:
Angular dependence of the magnetization of isotropic superconductors:
  which is the vortex direction?

abstract:
  We present studies of the dc magnetization of thin platelike samples of the
isotropic type II superconductor PbTl(10%), as a function of the angle between
the normal to the sample and the applied magnetic field ${\bf H}$. We determine
the magnetization vector ${\bf M}$ by measuring the components both parallel
and normal to ${\bf H}$ in a SQUID magnetometer, and we further decompose it in
its reversible and irreversible contributions. The behavior of the reversible
magnetization is well understood in terms of minimization of the free energy
taking into account geometrical effects. In the mixed state at low fields, the
dominant effect is the line energy gained by shortening the vortices, thus the
flux lines are almost normal to the sample surface. Due to the geometrical
constrain, the irreversible magnetization ${\bf M}_{irr}$ remains locked to the
sample normal over a wide range of fields and orientations, as already known.
We show that in order to undestand the angle and field dependence of the
modulus of ${\bf M}_{irr}$, which is a measure of the vortex pinning, and to
correctly extract the field dependent critical current density, the knowledge
of the modulus and orientation of the induction field ${\bf B}$ is required.


title: Umklapp scattering in transport through a 1D wire of finite length

abstract:
  Suppression of electron current $ \Delta I$ through a 1D channel of length
$L$ connecting two Fermi liquid reservoirs is studied taking into account the
Umklapp interaction induced by a periodic potential. This interaction opens
band gaps at the integer fillings and Hubbard gaps $2m$ at some rational
fillings in the infinite wire: $L \to \infty$. In the perturbative regime where
$m \ll v_c/L$ ($v_c:$ charge velocity), and for small deviations $\delta n$ of
the electron density from its commensurate values $- \Delta I/V$ can diverge
with some exponent as voltage or temperature $V,T$ decreases above
$E_c=max(v_c/L,v_c \delta n)$, while it goes to zero below $E_c$. This results
in a non-monotonous behavior of the conductance. In the case when the Umklapp
interaction creates a large Mott-Hubbard gap $2m \gg T_L $ inside the wire, the
transport is suppressed near half-filling everywhere inside the gap except for
an exponentially small region of $V,T < T_L exp(-2m/T_L)$.


title:
A generalization of the spherical model: Reentrant phase transition in
  the spin one ferromagnet

abstract:
  By mapping the hamiltonian of the spin one ferromagnet onto that of the
classical spherical model we investigate the possible phase transitions and the
phase diagram of the spin one ferromagnet. Similarly to what happens in the
spherical model we find no phase transition in one and two dimensions.
Nonetheless, for three dimensions we obtain a phase diagram in which the most
important and unexpected feature is the existence of a
ferromagnetic-paramagnetic transition at low temperatures.


title:
Hysteresis properties at zero temperature in the Dipolar-Random Field
  Ising Model

abstract:
  We present a modified two-dimensional random field Ising model, where a
dipolar interaction term is added to the classic random field Hamiltonian. In a
similar model it was already verified that the system state can exhibit domains
in the form of stripe patterns, typical of thin materials with strong
perpendicular anisotropy. In this work we show that the hysteresis loops
obtained at zero temperature can display a strict similarity with the loops
obtained in thin magnetic materials such as garnet films. In our model the
processes of domain nucleation and domain wall motion are well separated in
time as the system evolves. This remarkable fact allowed us to better
understand the nucleation process in this family of spin systems.


title: Dipolar random field Ising model: an application to garnet films

abstract:
  The dipolar-random field Ising model (DRFIM) recently introduced displays a
behaviour that can be connected to the magnetization of bidimensional magnetic
media. Epitaxial magnetic garnet films seem to be the ideal test material for
such a model. In this work the results of the measurements performed on garnet
samples are presented, as well as the comparisons with simulation results
obtained by the DRFIM. The results prove that a variety of hysteresis loops are
well described by the DRFIM. This capability does not derive from the fine
tuning of a great number of parameters, but by the interplay of exchange and
dipolar interactions.


title: Cluster Analysis and Finite-Size Scaling for Ising Spin Systems

abstract:
  Based on the connection between the Ising model and a correlated percolation
model, we calculate the distribution function for the fraction ($c$) of lattice
sites in percolating clusters in subgraphs with $n$ percolating clusters,
$f_n(c)$, and the distribution function for magnetization ($m$) in subgraphs
with $n$ percolating clusters, $p_n(m)$. We find that $f_n(c)$ and $p_n(m)$
have very good finite-size scaling behavior and they have universal finite-size
scaling functions for the model on square, plane triangular, and honeycomb
lattices when aspect ratios of these lattices have the proportions 1:$\sqrt
3$/2:$\sqrt 3$. The complex structure of the magnetization distribution
function $p(m)$ for the system with large aspect ratio could be understood from
the independent orientations of two or more percolation clusters in such
system.


title: The Wess-Zumino term and quantum tunneling

abstract:
  The significance of the Wess--Zumino term in spin tunneling is explored, and
a formula is established for the splitting of energy levels of a particle with
large fermionic spin as an applied magnetic field is switched on.


title:
Characterization of All-Chromium Tunnel Junctions and Single Electron
  Tunneling Devices Fabricated by Direct-Writing Multilayer Technique

abstract:
  We report about the fabrication and analysis of the properties of Cr/CrO_x/Cr
tunnel junctions and SET transistors, prepared by different variants of
direct-writing multilayer technique. In all cases, the CrO_x tunnel barriers
were formed in air under ambient conditions. From the experiments on single
junctions, values for the effective barrier height and thickness were derived.
For the Cr/CrO_x/Cr SET transistors we achieved minimal junction areas of 17 x
60 nm^2 using a scanning transmission electron microscope for the e-beam
exposure on Si_3N_4 membrane substrate. We discuss the electrical performance
of the transistor samples as well as their noise behavior.


title:
Operation characteristics of piezoelectric quartz tuning forks in high
  magnetic fields at liquid helium temperatures

abstract:
  Piezoelectric quartz tuning forks are investigated in view of their use as
force sensors in dynamic mode scanning probe microscopy at temperatures down to
1.5 K and in magnetic fields up to 8 T. The mechanical properties of the forks
are extracted from the frequency dependent admittance and simultaneous
interferometric measurements. The performance of the forks in a cryogenic
environment is investigated. Force-distance studies performed with these
sensors at low temperatures are presented.


title: Radiative transfer theory for vacuum fluctuations

abstract:
  A semiclassical kinetic theory is presented for the fluctuating photon flux
emitted by a disordered medium in thermal equilibrium. The kinetic equation is
the optical analog of the Boltzmann-Langevin equation for electrons. Vacuum
fluctuations of the electromagnetic field provide a new source of fluctuations
in the photon flux, over and above the fluctuations due to scattering. The
kinetic theory in the diffusion approximation is applied to the
super-Poissonian noise due to photon bunching and to the excess noise due to
beating of incident radiation with the vacuum fluctuations.


title:
New type of antiferromagnetic polaron and bipolaron in HTc -
  superconductors

abstract:
  The possibility of formation of a new type of polaron based on the quantum
aniferromagnet (AF) model is reported. We take into account exchange
interactions between localized d-d spins of the AF, as well as the p-d
interaction of the AF with p-carriers.
  The energy minimum is found when maximum charge density occurs on every
second spin. The formation of such ``comb''-like polarons results from the
damping of quantum fluctuations and the appearance of Van Vleck-like staggered
magnetization. Such polarons tend to form pairs coupled by an AF ``glue''.


title: Off-equilibrium dynamics in a singular diffusion model

abstract:
  We introduce a schematic non-linear diffusion model where density
fluctuations induce a rich out of equilibrium dynamics. The properties of the
model are studied by numerical simulations and analytically in a mean field
approximation. At low temperatures and high densities we find a long
off-equilibrium glassy region, where the system evolves out of an initially
pinned state showing aging and a slow decay of the autocorrelation as an
enhanced power law, along with strong spatial heterogeneities and violation of
the fluctuation dissipation theorem.


title:
Local-energy density functionals for an N-dimensional electronic system
  in a magnetic field

abstract:
  We present a general approach for the construction of the exact
local-energy-density functionals for a uniform N-dimensional electronic system
in a magnetic field. For arbitrary dimension, we obtain explicit expressions
for the matter, kinetic, and exchange density functionals. In the zero-field
limit, we recover the usual N-dimensional Thomas-Fermi theory. As an
application of our results, we develop a current-density-functional theory, in
the spirit of the Thomas-Fermi-Dirac approximation, for an inhomogeneous
many-electron system in a magnetic field.


title:
Self-organized criticality in a model of biological evolution with long
  range interactions

abstract:
  In this work we study the effects of introducing long range interactions in
the Bak-Sneppen (BS) model of biological evolution. We analyze a recebtly
propopsed version of the BS model where the interactions decay as r^{-alpha};
in this way the first nearest neighbors model is recovered in the limit alpha
-> infinity, and the random neighbors version for alpha=0. We study the space
and time correlations and analize how the critical behavior of the system
changes with the parameter alpha. We also study the sensibility to initial
conditions of the model using the spreading of damage technique. We found that
the system displays several distinct critical regimes as alpha is varied from
alpha=0 to alpha -> infinity.


title:
Conductance of Two-Dimensional Imperfect Conductors: Does the Elastic
  Scattering Preclude from Localization at T=0?

abstract:
  The method is proposed adapted for calculating the T=0 conductance of
arbitrarily stretched disordered conducting strips in terms of the Kubo theory.
The 2D scattering problem is solved through exact one-dimensionalization in
mode representation (instead of quasiclassical) that enables to allow
reasonably for quantum interference of scattered waves as well as for the
effect of dephasing. The inter- and intra-mode scattering channels are shown to
play quite different role, the former being responsible for diffusive smearing
of the quantum levels whereas the latter for the interference effects. No
pronounced localization should reveal itself in wires with more then one
conducting mode, irrespective of their length, contrary to anticipations of the
scaling theory.


title:
Classical Quantization of Local Hall Conductivity in 2D Ballistic
  Systems

abstract:
  We study the linear Hall response of 2D ballistic system on inhomogeneous
magnetic field. We establish that in classical limit the Hall conductivity
response on local magnetic field is quantized in units of $\alpha_H \equiv
\frac{e^3}{2 \pi^2 \hbar c}$. The quantized value depends on the point where
the field is applied, this dependence being irregular in chaotic billiards. The
phenomenon allows for direct tracing of special electron trajectories that
belong to fractal repellor. We discuss how quantum effects smooth the
quantization.


title:
Relaxation effects in the charge-ordered state of
  La$_{0.5}$Ca$_{0.5}$MnO$_{3}$

abstract:
  We report an experimental study of the time dependence of the resistivity and
magnetization of charge-ordered La$_{0.5}$Ca$_{0.5}$MnO$_{3}$ under different
thermal and magnetic field conditions. A relaxation with a stretched
exponential time dependence has been observed at temperatures below the charge
ordering temperature. A model using a hierarchical distribution of relaxation
times can explain the data.


title: Random Costs in Combinatorial Optimization

abstract:
  The random cost problem is the problem of finding the minimum in an
exponentially long list of random numbers. By definition, this problem cannot
be solved faster than by exhaustive search. It is shown that a classical
NP-hard optimization problem, number partitioning, is essentially equivalent to
the random cost problem. This explains the bad performance of heuristic
approaches to the number partitioning problem and allows us to calculate the
probability distributions of the optimum and sub-optimum costs.


title:
Broken-symmetry-adapted Green function theory of condensed matter
  systems:towards a vector spin-density-functional theory

abstract:
  The group theory framework developed by Fukutome for a systematic analysis of
the various broken symmetry types of Hartree-Fock solutions exhibiting spin
structures is here extended to the general many body context using spinor-Green
function formalism for describing magnetic systems. Consequences of this theory
are discussed for examining the magnetism of itinerant electrons in nanometric
systems of current interest as well as bulk systems where a vector spin-density
form is required, by specializing our work to spin-density-functional
formalism. We also formulate the linear response theory for such a system and
compare and contrast them with the recent results obtained for localized
electron systems. The various phenomenological treatments of itinerant magnetic
systems are here unified in this group-theoretical description.


title: Model glasses coupled to two different heat baths

abstract:
  In a $p$-spin interaction spherical spin-glass model both the spins and the
couplings are allowed to change in the course of time. The spins are coupled to
a heat bath with temperature $T$, while the coupling constants are coupled to a
bath having temperature $T_{J}$. In an adiabatic limit (where relaxation time
of the couplings is much larger that of the spins) we construct a generalized
two-temperature thermodynamics. It involves entropies of the spins and the
coupling constants. The application for spin-glass systems leads to a standard
replica theory with a non-vanishing number of replicas, $n=T/T_J$. For $p>2$
there occur at low temperatures two different glassy phases, depending on the
value of $n$. The obtained first-order transitions have positive latent heat,
and positive discontinuity of the total entropy. This is the essentially
non-equilibrium effect. The predictions of longtime dynamics and infinite-time
statics differ only for $n<1$ and $p>2$. For $p=2$ correlation of the disorder
(leading to a non-zero $n$) removes the known marginal stability of the spin
glass phase. If the observation time is very large there occurs no
finite-temperature spin glass phase. In this case there are analogies with the
broken-ergodicity dynamics in the usual spin-glass models and non-equilibrium
(aging) dynamics. A generalized fluctuation-dissipation relation is derived.


title: Mixed State Hall Effect in a Twinned YBa2Cu3O7-d Single Crystal

abstract:
  Thanks to the 9 contacts deposited on the surface of a high quality YBCO
twinned single crystal, we investigate both vortex guided motion along twins
and the mixed state Hall effect. Firstly, we clearly identify the vortex phase
transition and show that, when the magnetic field is along the twin boundaries
(within about 2 degrees), the vortex solid is a Bose glass.
  Secondly, the effects of twins on the vortex dynamics are studied by
measuring the direction and magnitude of the total electric field while
rotating the current in the ab plane. We observe a partially guided vortex
motion along the dominating twin plane family, already apparent in the vortex
liquid, and becoming more and more pronounced as the temperature or the
magnetic field is reduced. There is no change related to the vortex phase
transition.
  Finally, the mixed state Hall effect is studied, with particular focus given
to the vortex phase transition. We show that the Hall resistivity scaling law
rho_xy=A*rho_xx^b remains unchanged in the vortex solid phase. For a magnetic
field along the twins, the exponent is b=2, corresponding to a constant Hall
conductivity. For a tilted magnetic field, we find b=1.4. In this case, the
Hall conductivity changes sharply at the vortex lattice melting, its slope
becoming much larger in the vortex solid. This effect is strongly current
dependent, and thus demonstrates that the Hall conductivity is pinning
dependent, hopefully solving a long term controversy. We also thoroughly review
the experimental data on the mixed state Hall effect, and discuss some
theoretical models concerning both the anomaly (a sign reversal of the Hall
effect) and the scaling law. A novel model for the Hall scaling law is given,
directly inspired from the theory of percolation in metallic conductors.


title: Electron Standing Wave Formation in Atomic Wires

abstract:
  Using the Landauer formulation of transport theory and tight binding models
of the electronic structure, we study electron transport through atomic wires
that form 1D constrictions between pairs of metallic nano-contacts. Our results
are interpreted in terms of electron standing waves formed in the atomic wires
due to interference of electron waves reflected at the ends of the atomic
constrictions. We explore the influence of the chemistry of the atomic
wire-metal contact interfaces on these standing waves and the associated
transport resonances by considering two types of atomic wires: gold wires
attached to gold contacts and carbon wires attached to gold contacts. We find
that the conductance of the gold wires is roughly $1 G_0 = 2 e^2/h$ for the
wire lengths studied, in agreement with experiments. By contrast, for the
carbon wires the conductance is found to oscillate strongly as the number of
atoms in the wire varies, the odd numbered chains being more conductive than
the even numbered ones, in agreement with previous theoretical work that was
based on a different model of the carbon wire and metal contacts.


title:
Spin-lattice relaxation in the mixed state of YBaCuO: Can we see
  Doppler-shifted d-wave quasiparticles?

abstract:
  We present calculations of the rate of planar Cu spin lattice relaxation in
the mixed state of YBaCuO due to (i) vortex vibrations and (ii) electron
spin-flip scattering. We emphasize that both mechanisms give position dependent
rates due to the presence of vortices, and hence the magnetization recovery is
characterized by a distribution of rates. We conclude that relaxation by vortex
vibrations is too slow to be a significant factor in this material. Using a
semiclassical model of Doppler shifted d-wave quasiparticles with a linear
dispersion around the nodes, our calculation of the relaxation rate from
electron spin-flip scattering shows partial agreement with experiment.


title: Stability of homogeneous magnetic phases in a generalized t-J model

abstract:
  We study the stability of homogeneous magnetic phases in a generalized t-J
model including a same-sublattice hopping t' and nearest-neighbor repulsion V
by means of the slave fermion-Schwinger boson representation of spin operators.
At mean-field order we find, in agreement with other authors, that the
inclusion of further-neighbor hopping and Coulomb repulsion makes the
compressibility positive, thereby stabilizing at this level the spiral and Neel
orders against phase separation. However, the consideration of Gaussian
fluctuation of order parameters around these mean-field solutions produces
unstable modes in the dynamical matrix for all relevant parameter values,
leaving only reduced stability regions for the Neel phase. We have computed the
one-loop corrections to the energy in these regions, and have also briefly
considered the effects of the correlated hopping term that is obtained in the
reduction from the Hubbard to the t-J model.


title:
Butterfly-like spectra and collective modes of antidot superlattices in
  magnetic fields

abstract:
  We calculate the energy band structure for electrons in an external periodic
potential combined with a perpendicular magnetic field. Electron-electron
interactions are included within a Hartree approximation. The calculated energy
spectra display a considerable degree of self-similarity, just as the
``Hofstadter butterfly.'' However, screening affects the butterfly, most
importantly the bandwidths oscillate with magnetic field in a characteristic
way. We also investigate the dynamic response of the electron system in the
far-infrared (FIR) regime. Some of the peaks in the FIR absorption spectra can
be interpreted mainly in semiclassical terms, while others originate from
inter(sub)band transitions.


title: pi states in Josephson Junction between He-3-B

abstract:
  We investigate the dependence of the current-phase relationship on the
orientation of the order parameter for a pinhole between two $^3$He-B
reservoirs. We show that, due to the internal spin structure of the superfluid,
the energy of the junction may have a relative minimum at phase difference
equals $\pi$ at low temperatures. The dependence of the supercurrent on the
direction of an applied magnetic field can be used to verify the present
mechanism for the ``$\pi$-states''.


title:
Low energy valence photoemission in the Anderson impurity model for Ce
  compounds

abstract:
  The valence level photoemission spectra in the Anderson impurity model for Ce
compounds at zero temperature are studied as a function of the photon energy
$\omega$. Most of former studies on Ce compounds are based on the sudden
approximation, which is valid in high energy region. For the photoemission in
the adiabatic limit of low energy region, one should consider the dipole matrix
elements and the hole-induced photoelectron scattering potential. We can manage
it by combining the time-evolution formalism and the $1/N_f$ scheme in a large
$f$-level degeneracy $N_f$. This gives the exact results as $N_f\to\infty$. In
view of experiments on the valence photoemission, two contributions of $4f$-
and band emissions are mixed. We study the separate $4f$ and band contributions
(from Ce $5d$) and total emission including the interference between two on an
equal footing with varying the photon energy. In the $4f$-emission case, we
also explore the effects of hole-induced scattering potential of the
photoelectron with respect to $\omega$. Its effects are found very similar to
the core level photoemission in shake down case with a localized charge
transfer excitation. Additionally, we examine the adiabatic-sudden transition
in valence level photoemission for the present localized system through the
simplified two-level model.


title:
Visibility diagrams and experimental stripe structure in the quantum
  Hall effect

abstract:
  We analyze various properties of the visibility diagrams that can be used in
the context of modular symmetries and confront them to some recent experimental
developments in the Quantum Hall Effect. We show that a suitable physical
interpretation of the visibility diagrams which permits one to describe
successfully the observed architecture of the Quantum Hall states gives rise
naturally to a stripe structure reproducing some of the experimental features
that have been observed in the study of the quantum fluctuations of the Hall
conductance. Furthermore, we exhibit new properties of the visibility diagrams
stemming from the structure of subgroups of the full modular group.


title: Exotic structures on magnetic multilayers

abstract:
  To characterize the possible magnetic structures created on magnetic
multilayers a model has been formulated and studied. The interlayer
inhomogeneous structures found indicate either (i) a regular periodic, (ii) a
quasiperiodic change in the magnetization or (iii) spatially chaotic glass
states. The magnetic structures created depend mainly on the ratio of the
magnetic anisotropy constant to the exchange constant.
  With the increase of this ratio the periodic structures first transform into
the quasiperiodic and then into the chaotic glass states. The same tendency
arises with the depolarization of the magnetic moments of the first layer
deposited on the substrate.


title:
Mesoscopic Analysis of Structure and Strength of Dislocation Junctions
  in FCC Metals

abstract:
  We develop a finite element based dislocation dynamics model to simulate the
structure and strength of dislocation junctions in FCC crystals. The model is
based on anisotropic elasticity theory supplemented by the explicit inclusion
of the separation of perfect dislocations into partial dislocations bounding a
stacking fault. We demonstrate that the model reproduces in precise detail the
structure of the Lomer-Cottrell lock already obtained from atomistic
simulations. In light of this success, we also examine the strength of
junctions culminating in a stress-strength diagram which is the locus of points
in stress space corresponding to dissolution of the junction.


title: Ageing and Rheology in Soft Materials

abstract:
  We study theoretically the role of ageing in the rheology of soft materials.
We define several generalized rheological response functions suited to ageing
samples (in which time translation invariance is lost). These are then used to
study ageing effects within a simple scalar model (the "soft glassy rheology"
or SGR model) whose constitutive equations relate shear stress to shear strain
among a set of elastic elements, with distributed yield thresholds, undergoing
activated dynamics governed by a "noise temperature", $x$. (Between yields,
each element follows affinely the applied shear.) For $1<x<2$ there is a
power-law fluid regime in which transients occur, but no ageing. For $x<1$, the
model has a macroscopic yield stress. So long as this yield stress is not
exceeded, ageing occurs, with a sample's apparent relaxation time being of
order its own age. The (age-dependent) linear viscoelastic loss modulus
$G''(\omega,t)$ rises as frequency is {\em lowered}, but falls with age $t$, so
as to always remain less than $G'(\omega,t)$ (which is nearly constant).
Significant ageing is also predicted for the stress overshoot in nonlinear
shear startup and for the creep compliance. Though obviously oversimplified,
the SGR model may provide a valuable paradigm for the experimental and
theoretical study of rheological ageing phenomena in soft solids.


title: Free expansion of Bose-Einstein condensates with quantized vortices

abstract:
  The expansion of Bose-Einstein condensates with quantized vortices is studied
by solving numerically the time-dependent Gross-Pitaevskii equation at zero
temperature. For a condensate initially trapped in a spherical harmonic
potential, we confirm previous results obtained by means of variational methods
showing that, after releasing the trap, the vortex core expands faster than the
radius of the atomic cloud. This could make the detection of vortices feasible,
by observing the depletion of the density along the axis of rotation. We find
that this effect is significantly enhanced in the case of anisotropic
disc-shaped traps. The results obtained as a function of the anisotropy of the
initial configuration are compared with the analytic solution for a
noninteracting gas in 3D as well as with the scaling law predicted for an
interacting gas in 2D.


title: Electronic structure without exchange?

abstract:
  The correlation holes for densities of equal and opposite spin around a test
electron are determined from the Schr\"{o}dinger equation with proper boundary
conditions. The traditional "exchange" term follows from the boundary condition
which respects a spacial exclusion principle for equal spins. The resulting
potential compares reasonably well with standard local density potentials and
should simplify extensions towards non-local effects.


title: Universality in metallic nanocohesion: a quantum chaos approach

abstract:
  Convergent semiclassical trace formulae for the density of states and
cohesive force of a narrow constriction in an electron gas, whose classical
motion is either chaotic or integrable, are derived. It is shown that mode
quantization in a metallic point contact or nanowire leads to universal
oscillations in its cohesive force: the amplitude of the oscillations depends
only on a dimensionless quantum parameter describing the crossover from chaotic
to integrable motion, and is of order 1 nano-Newton, in agreement with recent
experiments. Interestingly, quantum tunneling is shown to be described
quantitatively in terms of the instability of the classical periodic orbits.


title:
Dynamic electromagnetic response of three-dimensional Josephson junction
  arrays

abstract:
  We present a theoretical study on the dynamical properties of
three-dimensional arrays of Josephson junctions. Our results indicate that such
superconducting networks represent highly sensitive 3D-SQUIDs having some major
advantages in comparison with conventional planar SQUIDs. The voltage response
function of 3D-SQUIDs is directly related to the vector-character of external
electromagnetic fields. The theory developed here allows the three-dimensional
reconstruction of a detected external field including phase information about
the field variables. Applications include the design of novel magnetometers,
gradiometers and particle detectors.


title:
Temporally ordered collective creep and dynamic transition in the
  charge-density-wave conductor NbSe3

abstract:
  We have observed an unusual form of creep at low temperatures in the
charge-density-wave (CDW) conductor NbSe$_3$. This creep develops when CDW
motion becomes limited by thermally-activated phase advance past individual
impurities, demonstrating the importance of local pinning and related
short-length-scale dynamics. Unlike in vortex lattices, elastic collective
dynamics on longer length scales results in temporally ordered motion and a
finite threshold field. A first-order dynamic phase transition from creep to
high-velocity sliding produces "switching" in the velocity-field
characteristic.


title: Spin symmetry breaking in bilayer quantum Hall systems

abstract:
  Based on the construction of generalized Halperin wave functions, we predict
the possible existence of a large class of broken spin symmetry states in
bilayer quantum Hall structures, generalizing the recently suggested canted
antiferromgnetic phase to many fractional fillings. We develop the appropriate
Chern-Simons theory, and establish explicitly that the low-lying neutral
excitation is a Goldstone mode and that the charged excitations are bimerons
with continuously tunable (through the canted antiferromagnetic order
parameter) electric charge on the individual merons.


title: Theory of "ferrisuperconductivity" in $U_{1-x}Th_xBe_{13}$

abstract:
  We construct a two component Ginzburg-Landau theory with coherent pair motion
and incoherent quasiparticles for the phase diagram of $U_{1-x}Th_xBe_{13}$.
The two staggered superconducting states live at the Brillouin zone center and
the zone boundary, and coexist for temperatures $T\le T_{c2}$ at concentrations
$x_{c1}\approx 0.02\le x \le x_{c2}\approx 0.04$. We predict below $T_{c2}$
appearance of a charge density wave (CDW) and Be-sublattice distortion. The
distortion explains the $\mu$SR relaxation anomaly, and Th-impurity mediated
scattering of ultrasound to CDW fluctuations explains the attenuation peak.


title:
Semiclassical theory of the emission properties of wave-chaotic resonant
  cavities

abstract:
  We develop a perturbation theory for the lifetime and emission intensity for
isolated resonances in asymmetric resonant cavities. The inverse lifetime
$\Gamma$ and the emission intensity $I(\theta)$ in the open system are
expressed in terms of matrix elements of operators evaluated with eigenmodes of
the closed resonator. These matrix elements are calculated in a semiclassical
approximation which allows us to represent $\Gamma$ and $I(\theta)$ as sums
over the contributions of rays which escape the resonator by refraction.


title:
Glass transitions and dynamics in thin polymer films: dielectric
  relaxation of thin films of polystyrene

abstract:
  The glass transition temperature $T_{\rm g}$ and the temperature $T_{\alpha}$
corresponding to the peak in the dielectric loss due to the $\alpha$-process
have been simultaneously determined as functions of film thickness d through
dielectric measurements for polystyrene thin films supported on glass
substrate. The dielectric loss peaks have also been investigated as functions
of frequency for a given temperature. A decrease in $T_{\rm g}$ was observed
with decreasing film thickness, while $T_{\alpha}$ was found to remain almost
constant for $d>d_{\rm c}$ and to decrease drastically with decreasing d for
$d<d_{\rm c}$. Here, $d_{\rm c}$ is a critical thickness dependent on molecular
weight. The relaxation time of the $\alpha$-process was found to have a d
dependence similar to that of $T_{\alpha}$. The relaxation function for the
$\alpha$-process was obtained by using the observed frequency dependence of the
peak profile of the dielectric loss. The exponent $\beta_{{\tiny KWW}}$, which
was obtained from the relaxation functions, decreases as thickness decreases.
This suggests that the distribution of relaxation times for the
$\alpha$-process broadens with decreasing thickness. The thickness dependence
of $T_{\rm g}$ is directly related to the distribution of relaxation times for
the $\alpha$-process, not to the relaxation time itself.


title:
Peak Effect, Fishtail Effect and Plateau Effect : The Reentrant
  Amorphization of Vortex Matter in 2H-NbSe_2

abstract:
  The magnetic field dependence of the critical current is studied in single
crystal samples of the weak pinning type-II superconductor 2H-NbSe$_2$ in the
high temperature and the low field region of the (H,T) phase space, in the
vicinity of the reentrant peak effect. The experimental results demonstrate
various pinning regimes : a collective pinned quasi-ordered solid in the
intermediate field that is destabilized in favor of disordered vortex phases in
both high fields near H$_{c2}$ and at low fields near H$_{c1}$. The temperature
evolution of the pinning behavior demonstrates how the amorphous limit (where
the correlation volume is nearly field independent) is approached around the
so-called nose region of the reentrant peak effect boundary. Furthermore, the
data show that the rapid approach to the amorphous limit naturally yields a
peak effect, i.e., a peak in the critical current, in the high field regime,
but yields a ``plateau effect'' instead in the low field regime in an analogous
way. With increasing effective disorder the peak effect shifts away from
H$_{c2}$ and resembles a ``fishtail'' anomaly.


title: Lattice field theories with an energy current

abstract:
  We investigate a lattice scalar field theory in the presence of a bias
favouring the establishment of an energy current, as a model for stationary
nonequilibrium processes at low temperature in a non-integrable system. There
is a transition at a finite value of the bias to a gapless modulated phase
which carries a classical current; however, unlike in similar, integrable,
models, quantum effects also allow for a non-zero current at arbitrarily small
bias. The transition is second order in the magnetically disordered phase, but
is pre-empted by a first-order transition in the ferromagnetic case, at least
at the mean-field level.


title: Cluster Statistics of BTW Automata

abstract:
  The cluster statistics of BTW automata in the SOC states are obtained by
extensive computer simulation. Various moments of the clusters are calculated
and few results are compared with earlier available numerical estimates and
exact results. Reasonably good agreement is observed. An extended statistical
analysis has been made.


title:
Anisotropic magnetoresistive properties of La_{1-x}Ca_{x}MnO_{3} (x
  \approx 1/3) film at temperatures far below the Curie temperature

abstract:
  A sharp distinction between magnetoresistance (MR) behavior for the magnetic
fields applied perpendicular (H_{perp}) and parallel (H_{par}) to the film
plane is found in colossal-magnetoresistance film La_{1-x}Ca_{x}MnO_{3} (x
\approx 3). At increasing of H_{perp} the MR is first negative (at H_{perp} < 4
kOe), then positive (4 kOe < H_{perp} < 12 kOe), and then negative again
(H_{perp} > 12 kOe). At increasing of H_{par} the MR is positive below H_{par}
\simeq 6 kOe and negative above it. In both cases the magnetic field was
perpendicular to the current. The anisotropic behavior of this kind occurs only
at low temperatures (T < 18 K) and is quite different from the results of
previous studies.


title:
Density Matrix Renormalization Group Study of the $S=1/2$
  Antiferromagnetic Heisenberg Chains with Quasiperiodic Exchange Modulation

abstract:
  The low energy behavior of the $S=1/2$ antiferromagnetic Heisenberg chains
with precious mean quasiperiodic exchange modulation is studied by the density
matrix renormalization group method. Based on the scaling behavior of the
energy gap distribution, it is found that the ground state of this model
belongs to the universality class different from that of the XY chain for which
the precious mean exchange modulation is marginal. This result is consistent
with the recent bosonization analysis of Vidal et al.


title: Diffusion Thermopower of Ferromagnetic Transition metals

abstract:
  This paper discusses a simple calculation for the diffusion thermopower of a
transition metal ferromagnet. The main result of this calculation is that
unlike in the case of a free-electron model, the diffusion thermopower S and
its derivative with respect to temperature dS/dT have opposite signs. The
results of this calculation agree qualitatively with experimental results in
the high temperature region, where the diffusion thermopower is dominant.


title: Nuclear spin relaxation rates in two-leg spin ladders

abstract:
  Using the transfer-matrix DMRG method, we study the nuclear spin relaxation
rate 1/T_1 in the two-leg s=1/2 ladder as function of the inter-chain
(J_{\perp}) and intra-chain (J_{|}) couplings. In particular, we separate the
q_y=0 and \pi contributions and show that the later contribute significantly to
the copper relaxation rate ^{63}(1/T_1) in the experimentally relevant coupling
and temperature range. We compare our results to both theoretical predictions
and experimental measures on ladder materials.


title:
High-Tc Superconductors in Applied Magnetic Fields Parallel to the CuO
  Planes: First Order Transition with Slow Onset of Resistivity

abstract:
  The three dimensional uniformly frustrated XY model is used as a model of a
high temperature superconductor in an applied magnetic field parallel to the
CuO-planes. Through Monte Carlo simulations with anisotropy $\eta^2 = 10$ on
large lattices we find evidence for a first order transition. Earlier
simulations and theoretical treatments are discussed and the experimentally
found smooth onset of resistivity is suggested to be due to a large potential
barrier against vortex line motion above $T_c$ present for perfect alignment of
the applied field.


title:
Quantum dot to disordered wire crossover: A complete solution in all
  length scales for systems with unitary symmetry

abstract:
  We present an exact solution of a supersymmetric nonlinear sigma model
describing the crossover between a quantum dot and a disordered quantum wire
with unitary symmetry. The system is coupled ideally to two electron reservoirs
via perfectly conducting leads sustaining an arbitrary number of propagating
channels. We obtain closed expressions for the first three moments of the
conductance, the average shot-noise power and the average density of
transmission eigenvalues. The results are complete in the sense that they are
nonperturbative and are valid in all regimes and length scales. We recover
several known results of the recent literature by taking particular limits.


title:
Hard-sphere solids near close packing: Testing theories for
  crystallization

abstract:
  The freezing transition of hard spheres has been well described by various
versions of density-functional theory (DFT). These theories should possess the
close-packed crystal as a special limit, which represents an extreme testing
ground for the quality of such liquid-state based theories. We therefore study
the predictions of DFT for the structure and thermodynamics of the hard-sphere
crystal in this limit. We examine the Ramakrishnan-Yussouff (RY) approximation
and two variants of the fundamental-measure theory (FMT) developed by Rosenfeld
and coworkers. We allow for general shapes of the density peaks, going beyond
the common Gaussian approximation. In all cases we find that, upon approaching
close packing, the peak width vanishes proportionally to the free distance a
between the particles and the free energy depends logarithmically on a.
However, different peak shapes and next-to-leading contributions to the free
energy result from the different approximate functionals. For the RY theory,
within the Gaussian approximation, we establish that the crystalline solutions
form a closed loop with a stable and an unstable branch both connected to the
close-packing point at a=0, consistent with the absence of a liquid-solid
spinodal. That version of FMT that has previously been applied to freezing,
predicts asymptotically step-like density profiles confined to the cells of
self-consistent cell theory. But a recently suggested improved version which
employs tensor weighted densities yields wider and almost Gaussian peaks which
are shown to be in very good agreement with computer simulations.


title:
Competition between phase separation and "classical" intermediate
  valence in an exactly solved model

abstract:
  The exact solution of the spin-1/2 Falicov-Kimball model on an
infinite-coordination Bethe lattice is analyzed in the regime of ``classical''
intermediate valence. We find (i) either phase separation or a direct
metal-insulator transition preclude intermediate valence over a large portion
of the phase diagram and (ii) within the intermediate valence phase, only
continuous transitions are found as functions of the localized f-electron
energy or temperature.


title:
Quasi-long-range order in the random anisotropy Heisenberg model:
  functional renormalization group in 4-\epsilon dimensions

abstract:
  The large distance behaviors of the random field and random anisotropy O(N)
models are studied with the functional renormalization group in 4-\epsilon
dimensions. The random anisotropy Heisenberg (N=3) model is found to have a
phase with the infinite correlation radius at low temperatures and weak
disorder. The correlation function of the magnetization obeys a power law <
m(x) m(y) >\sim |x-y|^{-0.62\epsilon}. The magnetic susceptibility diverges at
low fields as \chi \sim H^{-1+0.15\epsilon}. In the random field O(N) model the
correlation radius is found to be finite at the arbitrarily weak disorder for
any N>3. The random field case is studied with a new simple method, based on a
rigorous inequality. This approach allows one to avoid the integration of the
functional renormalization group equations.


title:
Fluctuation Conductivity in Insulator-Superconductor Transitions with
  Dissipation

abstract:
  We analyze here the fluctuation conductivity in the vicinity of the critical
point in a 2D Josephson junction array shunted by an Ohmic resistor.We find
that at the Gaussian level, the conductivity acquires a logarithmic dependence
on $T/(T-T_c)$ when the dissipation is sufficiently small. In the renormalized
classical regime, this logarithmic dependence gives rise to a leveling-off of
the resistivity at low to intermediate temperatures when fluctuations are
included. We show, however, that this trend does not persist to T=0 at which
point the resistivity vanishes. The possible relationship of the leveling of
the resistivity to the low temperature transport in granlar superconductors is
discussed.


title:
Internal Transitions of Two-Dimensional Charged Magneto-Excitons X-:
  Theory and Experiment

abstract:
  Internal spin-singlet and spin-triplet transitions of charged excitons X- in
magnetic fields in quantum wells have been studied experimentally and
theoretically. The allowed X- transitions are photoionizing and exhibit a
characteristic double-peak structure, which reflects the rich structure of the
magnetoexciton continua in higher Landau levels (LL's). We discuss a novel
exact selection rule, a hidden manifestation of translational invariance, that
governs transitions of charged mobile complexes in a magnetic field.


title: Glassy transition in a disordered model for the RNA secondary structure

abstract:
  We numerically study a disordered model for the RNA secondary structure and
we find that it undergoes a phase transition, with a breaking of the replica
symmetry in the low temperature region (like in spin glasses). Our results are
based on the exact evaluation of the partition function.


title: Statistics of energy levels and eigenfunctions in disordered systems

abstract:
  The article reviews recent developments in the theory of fluctuations and
correlations of energy levels and eigenfunction amplitudes in diffusive
mesoscopic samples. Various spatial geometries are considered, with emphasis on
low-dimensional (quasi-1D and 2D) systems. Calculations are based on the
supermatrix sigma-model approach. The method reproduces, in so-called zero-mode
approximation, the universal random matrix theory (RMT) results for the
energy-level and eigenfunction fluctuations. Going beyond this approximation
allows us to study system-specific deviations from universality, which are
determined by the diffusive classical dynamics in the system. These deviations
are especially strong in the far ``tails'' of the distribution function of the
eigenfunction amplitudes (as well as of some related quantities, such as local
density of states, relaxation time, etc.). These asymptotic ``tails'' are
governed by anomalously localized states which are formed in rare realizations
of the random potential. The deviations of the level and eigenfunction
statistics from their RMT form strengthen with increasing disorder and become
especially pronounced at the Anderson metal-insulator transition. In this
regime, the wave functions are multifractal, while the level statistics
acquires a scale-independent form with distinct critical features. Fluctuations
of the conductance and of the local intensity of a classical wave radiated by a
point-like source in the quasi-1D geometry are also studied within the
sigma-model approach. For a ballistic system with rough surface an
appropriately modified (``ballistic'') sigma-model is used. Finally, the
interplay of the fluctuations and the electron-electron interaction in small
samples is discussed, with application to the Coulomb blockade spectra.


title: Cotunneling through quantum dot with even number of electrons

abstract:
  We study an influence of a finite magnetic field on a small spin-degenerate
quantum dot with even number of electrons, attached to metallic leads. It is
shown that, under certain conditions, the low energy physics of the system can
be described by the S=1/2 antiferromagnetic Kondo model.


title:
Parallel Magnetic Field Induced Transition in Transport in the Dilute
  Two-Dimensional Hole System in GaAs

abstract:
  A magnetic field applied parallel to the two-dimensional hole system in the
GaAs/AlGaAs heterostructure, which is metallic in the absence of an external
magnetic field, can drive the system into insulating at a finite field through
a well defined transition. The value of resistivity at the transition is found
to depend strongly on density.


title:
Probing Entanglement and Non-locality of Electrons in a Double-Dot via
  Transport and Noise

abstract:
  Addressing the feasibilty of quantum communication with electrons we consider
entangled spin states of electrons in a double-dot which is weakly coupled to
in--and outgoing leads. We show that the entanglement of two electrons in the
double-dot can be detected in mesoscopic transport and noise measurements. In
the Coulomb blockade and cotunneling regime the singlet and triplet states lead
to phase-coherent current and noise contributions of opposite signs and to
Aharonov-Bohm and Berry phase oscillations in response to magnetic fields.
These oscillations are a genuine two-particle effect and provide a direct
measure of non-locality in entangled states. We show that the ratio of
zero-frequency noise to current (Fano factor) is universal and equal to the
electron charge.


title:
Interacting Fermi liquid at finite temperature: Part I: Convergent
  Attributions

abstract:
  Using the method of continuous renormalization group around the Fermi
surface, we prove that a two-dimensional jellium interacting system of Fermions
at low temperature T is a Fermi liquid (analytic in the coupling constant g)
for g < const/|logT|, and satisfying uniform bounds on the first and second
derivatives of the selfenergy. This bound is also a step in the program of
rigorous (non-perturbative) study of the BCS phase transition for many Fermions
systems; it proves in particular that in dimension two the transition
temperature (if any) must be non-perturbative in the coupling constant. The
proof is organized into two parts: the present paper deals with the convergent
contributions, and a companion paper (Part II) deals with the renormalization
of dangerous two point subgraphs and achieves the proof.


title:
Interacting Fermi liquid in two dimensions at finite temperature: Part
  II: Renormalization

abstract:
  This is a companion paper to cond-mat/9907130. Using the method of continuous
renormalization group around the Fermi surface and the results of
cond-mat/9907130, we achieve the proof that a two-dimensional jellium
interacting system of Fermions at low temperature T is a Fermi liquid (analytic
in the coupling constant g) for g < const./|log T| and satisfying uniform
bounds on the first and second derivatives of the selfenergy. This proves that
in two dimensions the transition temperature (if any) must be non-perturbative,
and is a step in the program of rigorous study of the BCS phase transition
using methods of constructive field theory.


title:
Diffusons, Locons, Propagons: Character of Atomic Vibrations in
  Amorphous Si

abstract:
  Numerical studies of amorphous silicon show that the lowest 4% of vibrational
modes are plane-wave like ("propagons") and the highest 3% of modes are
localized ("locons"). The rest are neither plane-wave like nor localized. We
call them "diffusons." Since diffusons are by far the most numerous, we try to
characterize them by calculating such properties as wavevector and polarization
(which seem not to be useful), "phase quotient" (a measure of the change of
vibrational phase on between first neighbor atoms), spatial polarization
memory, and diffusivity. Localized states are characterized by finding decay
lengths, inverse participation ratios, and coordination numbers of the atoms
participating.


title:
Quantum Computing and Quantum Communication with Electrons in
  Nanostructures

abstract:
  If the states of spins in solids can be created, manipulated, and measured at
the single-quantum level, an entirely new form of information processing,
quantum computing and quantum communication, will be possible. We review our
proposed spin-quantum dot architecture for a quantum computer and review some
recent results on a deterministic source of entanglement generated by coupling
quantum dots. Addressing the feasibility of quantum communication with
entangled electrons we consider a scattering set-up with an entangler and beam
splitter where the current noise exhibits bunching behavior for electronic
singlet states and antibunching behavior for triplet states. We show that spin
currents can produce noise even in the absence of any charge currents.


title: Exactly solvable quantum spin tubes and ladders

abstract:
  We find families of integrable n-leg spin-1/2 ladders and tubes with general
isotropic exchange interactions between spins. These models are equivalent to
su(N) spin chains with N=2^n. Arbitrary rung interactions in the spin tubes and
ladders induce chemical potentials in the equivalent spin chains. The
potentials are n-dependent and differ for the tube and ladder models. The
models are solvable by means of nested Bethe Ansatz.


title:
Barriers in the p-spin interacting spin-glass model. The dynamical
  approach

abstract:
  We investigate the barriers separating metastable states in the spherical
p-spin glass model using the instanton method. We show that the problem of
finding the barrier heights can be reduced to the causal two-real-replica
dynamics. We find the probability for the system to escape one of the highest
energy metastable states and the energy barrier corresponding to this process.


title:
Collective Dynamics of Josephson Vortices in Intrinsic Josephson
  Junctions :Exploration of In-phase Locked Superradiant Vortex Flow States

abstract:
  In order to clarify the ``superradiant'' conditions for the moving Josephson
vortices to excite in-phase AC electromagnetic fields over all junctions, we
perform large scale simulations of realistic dimensions for intrinsic Josephson
junctions under the layer parallel magnetic field. Three clear step-like
structures in the I-V curve are observed above a certain high field ($H > 1T$
in the present simulations), at which we find structural transitions in the
moving flux-line lattice. The Josephson vortex flow states are accordingly
classified into four regions (region I $\sim $ IV with increasing current), in
each of which the power spectrum for the electric field oscillations at the
sample edge are measured and typical snapshots for Josephson vortex
configurations are displayed. Among the four regions, especially in the region
III, an in-phase rectangular vortex lattice flow state emerges and the power
spectrum shows remarkably sharp peak structure, i.e., superradiant state.
Comparison of the simulation results with an eigenmode analysis for the
transverse propagating Josephson plasma oscillations reveals that the
resonances between Josephson vortex flow states and some of the eigenmodes are
responsible for the clear flux lattice structural transitions. Furthermore, the
theoretical analysis clarifies that the width of the superradiant state region
in the I-V characteristics enlarges with decreasing both the superconducting
and insulating layer thickness.


title: Hidden non-Fermi liquid behavior due to crystal field quartet

abstract:
  We study a realistic Kondo model for crystal field quartet ground states
having magnetic and non-magnetic (quadrupolar) exchange couplings with
conduction electrons, using the numerical renormalization group method. We
focus on a local effect dependent on singlet excited states coupled to the
quartet, which reduces the non-magnetic coupling significantly and drives
non-Fermi liquid behavior observed in the calculated quadrupolar
susceptibility. A crossover from the non-Fermi liquid state to the Fermi liquid
state is characterized by a small energy scale very sensitive to the
non-magnetic coupling. On the other hand, the Kondo temperature observed in the
magnetic susceptibility is less sensitive. The different crystal-field
dependence of the two exchange couplings may be related to the different $x$
dependence of quadrupolar and magnetic ordering temperatures in
Ce$_x$La$_{1-x}$B$_6$.


title:
Nonperturbative XY-model approach to strong coupling superconductivity
  in two and three dimensions

abstract:
  For an electron gas with delta-function attraction we investigate the
crossover from weak- to strong-coupling supercoductivity in two and three
dimensions. We derive analytic expressions for the stiffness of phase
fluctuations and set up effective XY-models which serve to determine
nonperturbatively the temperature of phase decoherence where superconductivity
breaks down. We find the transition temperature T_c as a monotonous function of
the coupling strength and carrier density both in two and three dimensions, and
give analytic formulas for the merging of the temperature of phase decoherence
with the temperature of pair formation in the weak-coupling limit.


title:
Exact Charge Dynamics in the Supersymmetric t-J Model with
  Inverse-Square Interaction

abstract:
  Dynamical charge structure factor $N(Q,\omega)$ with $Q$ smaller than the
Fermi wave number is derived analytically for the one-dimensional
supersymmetric t-J model with $1/r^2$ interaction. Strong spin-charge
separation in dynamics is found. $N(Q,\omega)$ with given electron density does
not depend on the spin polarization for arbitrary size of the system. In the
thermodynamic limit, only two holons and one antiholon contribute to
$N(Q,\omega)$. These results together with generalized ones for the SU($K$,1)
supersymmetric t-J model are derived via solution of the Sutherland model in
the strong coupling limit.


title:
Relativistic effects in the electronic structure for the 3d paramagnetic
  ions

abstract:
  It has been shown that relativistic spin-orbit effects have enormous
influence on the electronic structure of the correlated electron systems 3dn.
The s-o coupling produces the fine electronic structure with a large number of
low- energy, < 10 meV, localized states, These states affect enormously
electronic and magnetic properties of 3d-ion compounds at low- and
room-temperature regions. It is inferred that the relativistic s-o effects and
the multiplet structure on individual atoms are indispensable for the proper
evaluation of the electronic structure of paramagnetic 3d ions.


title:
Anomalous temperature dependences of the susceptibility for the one-3d-
  electron cation

abstract:
  We have studied properties of the one-3d-electron cation (Ti 3+, V 4+ ions)
under the action of the low-symmetry crystal field in the presence of the spin-
orbit coupling. Very anomalous temperature dependences of the magnetic
susceptibility chi (T) have been obtained as resulting from the off-cubic
lattice distortion provided the intra-atomic spin-orbit coupling is taken into
account. It indicates that, despite of the weakness of the spin-orbit coupling,
the one 3d electron in a solid cannot be treated as a free S=1/2 spin. The same
holds for compounds containing the Ti 3+ and V4+ ions.


title: Loop Algorithms for Asymmetric Hamiltonians

abstract:
  Generalized rules for building and flipping clusters in the quantum Monte
Carlo loop algorithm are presented for the XXZ-model in a uniform magnetic
field along the Z-axis. As is demonstrated for the Heisenberg antiferromagnet
it is possible from these rules to select a new algorithm which performs
significantly better than the standard loop algorithm in strong magnetic fields
at low temperatures.


title:
Entropy production, energy dissipation and violation of Onsager
  relations in the steady glassy state

abstract:
  In a glassy system different degrees of freedom have well-separated
characteristic times, and are described by different temperatures. The
stationary state is essentially non-equilibrium. A generalized statistical
thermodynamics is constructed and a universal variational principle is
proposed. Entropy production and energy dissipation occur at a constant rate;
there exists a universal relation between them, valid to leading order in the
small ratio of the characteristic times. Energy dissipation (unlike entropy
production) is closely connected to the fluctuations of the slow degree.
Corrections due to a finite ratio of the times are obtained. Onsager relations
in the context of heat transfer are also considered. They are always broken in
glassy states, except close to equilibrium.


title: Simple model with facilitated dynamics for granular compaction

abstract:
  A simple lattice model is used to study compaction in granular media. As in
real experiments, we consider a series of taps separated by large enough
waiting times. The relaxation of the density exhibits the characteristic
inverse logarithmic law. Moreover, we have been able to identify analytically
the relevant time scale, leading to a relaxation law independent of the
specific values of the parameters. Also, an expression for the asymptotic
density reached in the compaction process has been derived. The theoretical
predictions agree fairly well with the results from the Monte Carlo simulation.


title: Wave scattering from self-affine surfaces

abstract:
  Electromagnetic wave scattering from a perfectly reflecting self-affine
surface is considered. Within the framework of the Kirchhoff approximation, we
show that the scattering cross section can be exactly written as a function of
the scattering angle via a centered symmetric Levy distribution for general
roughness amplitude, Hurst exponent and wavelength of the incident wave. The
amplitude of the specular peak, its width and its position are discussed as
well as the power law decrease (with scattering angle) of the scattering cross
section.


title:
Probing the electron-electron interaction in a diffusive gold wire using
  a controllable Josephson junction

abstract:
  We have studied the critical current of a diffusive superconductor - normal
metal - superconductor (SNS) Josephson junction as a function of the electron
energy distribution in the normal region. This was realized in a 4 terminal
device, in which a mesoscopic gold wire between two electron reservoirs is
coupled in its center to two superconducting electrodes. By varying the length
of the wire and applying a voltage over it we are able to control the electron
distribution function in the center of the wire, which forms the normal region
of the SNS junction. The observed voltage and temperature dependence are in
good agreement with the existing theory on diffusive SNS junctions, except for
low energies. However, an electron-electron interaction time $\tau_0$ =10 ps
was found, which is three orders of magnitude faster than expected from theory.


title:
Localized magnetoplasmon modes arising from broken translational
  symmetry in semiconductor superlattices

abstract:
  The electromagnetic propagator associated with the localized collective
magnetoplasmon excitations in a semiconductor superlattice with broken
translational symmetry, is calculated analytically within linear response
theory. We discuss the properties of these collective excitations in both
radiative and non-radiative regimes of the electromagnetic spectra. We find
that low frequency retarded modes arise when the surface density of carriers at
the symmetry breaking layer is lower than the density at the remaining layers.
Otherwise a doublet of localized, high-frequency magnetoplasmon-like modes
occurs.


title:
Mesoscopic fluctuations of the ground state spin of a small metal
  particle

abstract:
  We study the statistical distribution of the ground state spin for an
ensemble of small metallic grains, using a random-matrix toy model. Using the
Hartree Fock approximation, we find that already for interaction strengths well
below the Stoner criterion there is an appreciable probability that the ground
state has a finite, nonzero spin. Possible relations to experiments are
discussed.


title: Phase ordering in chaotic map lattices with conserved dynamics

abstract:
  Dynamical scaling in a two-dimensional lattice model of chaotic maps, in
contact with a thermal bath, is numerically studied. The model here proposed is
equivalent to a conserved Ising model with coupligs which fluctuate over the
same time scale as spin moves. When couplings fluctuations and thermal
fluctuations are both important, this model does not belong to the class of
universality of a Langevin equation known as model B; the scaling exponents are
continuously varying with the temperature and depend on the map used. The
universal behavior of model B is recovered when thermal fluctuations are
dominant.


title: Order Parameter "Holes" and Theory of Microwave Conductivity in YBCO

abstract:
  We propose that the low temperature discrepancy between simple d-wave models
of the microwave conductivity and existing experiments on single crystals of
YBCO can be resolved by including the scattering of quasiparticles from "holes"
of the order parameter at impurity sites. Within a framework proposed
previously, we find in particular excellent agreement with data of Hosseini et
al. on slightly overdoped YBCO samples over the entire temperature range down
to about 2-3K, and for a wide range of frequencies. Remaining discrepancies in
the "universal" regime at very low temperatures are discussed.


title:
Interactions and Interference in Quantum Dots: Kinks in Coulomb Blockade
  Peak Positions

abstract:
  We investigate the spin of the ground state of a geometrically confined
many-electron system. For atoms, shell structure simplifies this problem-- the
spin is prescribed by the well-known Hund's rule. In contrast, quantum dots
provide a controllable setting for studying the interplay of quantum
interference and electron-electron interactions in general cases. In a generic
confining potential, the shell-structure argument suggests a singlet ground
state for an even number of electrons. The interaction among the electrons
produces, however, accidental occurrences of spin-triplet ground states, even
for weak interaction, a limit which we analyze explicitly. Variaton of an
external parameter causes sudden switching between these states and hence a
kink in the conductance. Experimental study of these kinks would yield the
exchange energy for the ``chaotic electron gas''.


title:
Oscillatory Tunnel Splittings in Spin Systems: A Discrete
  Wentzel-Kramers-Brillouin Approach

abstract:
  Certain spin Hamiltonians that give rise to tunnel splittings that are viewed
in terms of interfering instanton trajectories, are restudied using a discrete
WKB method, that is more elementary, and also yields wavefunctions and
preexponential factors for the splittings. A novel turning point inside the
classically forbidden region is analysed, and a general formula is obtained for
the splittings. The result is appled to the \Fe8 system. A previous result for
the oscillation of the ground state splitting with external magnetic field is
extended to higher levels.


title: QHE Today

abstract:
  I present a brief survey of important recent developments in the quantum Hall
effect. The review covers both fractional and integer regimes, from an
experimentalist's perspective. The topics include direct measurement of
fractional charge, composite fermion Fermi surface, spin textures, and edge
state (chiral Luttinger liquid) dynamics.


title: Spin Tunneling and Phonon-assisted Relaxation in Mn12-acetate

abstract:
  We present a comprehensive theory of the magnetization relaxation in a
Mn12-acetate crystal in the high-temperature regime (T>1 K), which is based on
phonon-assisted spin tunneling induced by quartic magnetic anisotropy and weak
transverse magnetic fields. The overall relaxation rate as function of the
longitudinal magnetic field is calculated and shown to agree well with
experimental data including all resonance peaks measured so far. The Lorentzian
shape of the resonances, which we obtain via a generalized master equation that
includes spin tunneling, is also in good agreement with recent data. We derive
a general formula for the tunnel splitting energy of these resonances. We show
that fourth-order diagonal terms in the Hamiltonian lead to satellite peaks. A
derivation of the effective linewidth of a resonance peak is given and shown to
agree well with experimental data. In addition, previously unknown spin-phonon
coupling constants are calculated explicitly. The values obtained for these
constants and for the sound velocity are also in good agreement with recent
data. We show that the spin relaxation in Mn12-acetate takes place via several
transition paths of comparable weight. These transition paths are expressed in
terms of intermediate relaxation times, which are calculated and which can be
tested experimentally.


title: Elastic Effects in Disordered Nematic Networks

abstract:
  Elastic effects in a model of disordered nematic elastomers are numerically
investigated in two dimensions. Networks crosslinked in the isotropic phase
exhibit unusual soft mechanical response against stretching. It arises from
gradual alignment of orientationally correlated regions that are elongated
along the director. A sharp crossover to a macroscopically aligned state is
obtained on further stretching. The effect of random internal stress is also
discussed.


title:
Spectrum of surface-mode contributions to the excitation probability for
  electron beam interacting with sharp-edged dielectric wedges

abstract:
  The interaction of a nonrelativistic charged particle beam, travelling
parallel to the surface of a sharp-edged dielectric wedge is analyzed. The
general expressions for excitation probability are obtained for a beam moving
along the direction of a symmetry axis, either outside or inside the dielectric
wedge. The dielectric function of the medium is assumed to be isotropic, and
numerical results are given for the materials of experimental interest.


title: Scaling of waves in the Bak-Tang-Wiesenfeld sandpile model

abstract:
  We study probability distributions of waves of topplings in the
Bak-Tang-Wiesenfeld model on hypercubic lattices for dimensions D>=2. Waves
represent relaxation processes which do not contain multiple toppling events.
We investigate bulk and boundary waves by means of their correspondence to
spanning trees, and by extensive numerical simulations. While the scaling
behavior of avalanches is complex and usually not governed by simple scaling
laws, we show that the probability distributions for waves display clear power
law asymptotic behavior in perfect agreement with the analytical predictions.
Critical exponents are obtained for the distributions of radius, area, and
duration, of bulk and boundary waves. Relations between them and fractal
dimensions of waves are derived. We confirm that the upper critical dimension
D_u of the model is 4, and calculate logarithmic corrections to the scaling
behavior of waves in D=4. In addition we present analytical estimates for bulk
avalanches in dimensions D>=4 and simulation data for avalanches in D<=3. For
D=2 they seem not easy to interpret.


title:
Universal conductance fluctuations in three dimensional metallic single
  crystals of Si

abstract:
  In this paper we report the measurement of conductance fluctuations in single
crystals of Si made metallic by heavy doping (n \approx 2-2.5n_c, n_c being
critical composition at Metal-Insulator transition). Since all dimensions (L)
of the samples are much larger than the electron phase coherent length L_\phi
(L/L_\phi \sim 10^3), our system is truly three dimensional. Temperature and
magnetic field dependence of noise strongly indicate the universal conductance
fluctuations (UCF) as predominant source of the observed magnitude of noise.
Conductance fluctuations within a single phase coherent region of L_\phi^3 was
found to be saturated at <(\delta G_\phi)^2> \approx (e^2/h)^2. An accurate
knowledge of the level of disorder, enables us to calculate the change in
conductance \delta G_1 due to movement of a single scatterer as \delta G_1 \sim
e^2/h, which is \sim 2 orders of magnitude higher than its theoretically
expected value in 3D systems.


title:
Pseudo-gap features of intrinsic tunneling in (HgBr_2)-Bi2212 single
  crystals

abstract:
  The c-axis tunneling properties of both pristine Bi2212 and its HgBr$_2$
intercalate have been measured in the temperature range 4.2 - 250 K.
Lithographically patterned 7-10 unit-cell heigh mesa structures on the surfaces
of these single crystals were investigated. Clear SIS-like tunneling curves for
current applied in the $\it c$-axis direction have been observed. The dynamic
conductance d$I/$d$V(V)$ shows both sharp peaks corresponding to a
superconducting gap edge and a dip feature beyond the gap, followed by a wide
maximum, which persists up to a room temperature. Shape of the temperature
dependence of the {\it c}-axis resistance does not change after the
intercalation suggesting that a coupling between $\rm CuO_2$-bilayers has
little effect on the pseudogap.


title:
A quasi-unit cell model for Al-Ni-Co Ideal Quasicrystal based on
  clusters with broken 10-fold symmetry

abstract:
  We present new evidence supporting the quasi-unit cell description of the
$Al_{72}Ni_{20}Co_{8}$ decagonal quasicrystal which shows that the solid is
composed of repeating, overlapping decagonal cluster columns with broken
10-fold symmetry. We propose an atomic model which gives a significantly
improved fit to electron microscopy experiments compared to a previous proposal
by us and to alternative proposals with 10-fold symmetric clusters.


title:
Scaling of the distribution of price fluctuations of individual
  companies

abstract:
  We present a phenomenological study of stock price fluctuations of individual
companies. We systematically analyze two different databases covering
securities from the three major US stock markets: (a) the New York Stock
Exchange, (b) the American Stock Exchange, and (c) the National Association of
Securities Dealers Automated Quotation stock market. Specifically, we consider
(i) the trades and quotes database, for which we analyze 40 million records for
1000 US companies for the 2-year period 1994--95, and (ii) the Center for
Research and Security Prices database, for which we analyze 35 million daily
records for approximately 16,000 companies in the 35-year period 1962--96. We
study the probability distribution of returns over varying time scales $\Delta
t$, where $\Delta t$ varies by a factor of $\approx 10^5$---from 5 min up to
$\approx$ 4 years. For time scales from 5~min up to approximately 16~days, we
find that the tails of the distributions can be well described by a power-law
decay, characterized by an exponent $\alpha \approx 3$ ---well outside the
stable L\'evy regime $0 < \alpha < 2$. For time scales $\Delta t \gg (\Delta
t)_{\times} \approx 16 $days, we observe results consistent with a slow
convergence to Gaussian behavior. We also analyze the role of cross
correlations between the returns of different companies and relate these
correlations to the distribution of returns for market indices.


title:
Controlled Dephasing via Phase Detection of Electrons: Demonstration of
  Bohr's Complementarity Principle

abstract:
  Interference results when a quantum particle is free to choose among a few
indistinguishable paths. A canonical example of Bohr's complementarity
principle [1] is a two-path interferometer with an external detector coupled to
one of the paths. Then, interference between the two paths vanishes (i.e.
dephasing) if one is able to detect, even in principle, the path taken by the
particle. This type of which path (WP) experiment was already executed with
photons, cooled atoms, neutrons, solitons, and more recently with electrons in
a mesoscopic system [2]. In the latter experiment path determination was
provided by inducing a change in the current flowing through the detector. In
the present experiment we perform a more intriguing WP determination: only a
phase change is being induced in the detector while the current remains
unaffected. We show that such detector-interferometer interaction can be
understood both, from the WP information obtained by the detector, or
alternatively by understanding the disturbance in the interferometer caused by
the detector. Moreover, we address the subtle role of detector coherency and
point out difficulties in the intuitive interpretation of the experiment.


title: Collimation Mechanism for Atom Lasers

abstract:
  A mechanism is suggested for creating well-collimated beams of neutral
spin-polarized particles by means of magnetic fields. This mechanism can be
used in atom lasers for the formation of directed coherent beams of atoms. The
directed motion of atoms is achieved only with the help of magnetic fields, no
mechanical collimators being involved.


title:
Critical Properties in Dynamical Charge Correlation Function for the
  One-Dimensional Mott Insulator

abstract:
  Critical properties in the dynamical charge correlation function for the
one-dimensional Mott insulator are studied. By properly taking into account
{\it the final-state interaction} between the charge and spin degrees of
freedom, we find that the edge singularity in the charge correlation function
is governed by massless spinon excitations, although it is naively expected
that spinons do not directly contribute to the charge excitation over the
Hubbard gap. We obtain the momentum-dependent anomalous critical exponent by
applying the finite-size scaling analysis to the Bethe ansatz solution of the
half-filled Hubbard model.


title:
Quasiparticle spectrum inside the vortex core: crossover from dirty to
  clean limit

abstract:
  The quasiparticle spectrum inside the vortex core in the mixed state of a
strongly type-II superconductors are studied. The s-wave symmetry for the gap
parameter is assumed. The crossover behavior from dirty to clean limit is shown
by numerical calculation based on the random matrix theory.


title:
Crossover between Fermi Liquid and non-Fermi Liquid in Orbitally
  Degenerate Kondo Systems

abstract:
  Entanglement of spin and orbital Kondo effect is investigated on the basis of
a Kondo-type exchange model with twofold orbital degeneracy. By using Wilson's
numerical renormalization-group method, we examine dynamical and thermal
properties respecting the difference in time-reversal property of multipole
operators. In the presence of particle-hole symmetry, the model has a new
non-Fermi-liquid fixed point with a fractional entropy. The spectral intensity
of the quadrupole susceptibility diverges in the zero-frequency limit, while
the dipole susceptibility shows a Fermi-liquid-like behavior. This is
understood by mapping to the two-channel Kondo model, in which the dipole
moment is mapped onto the operators with the scaling dimension $\Delta_m=1$,
while the quadrupole moment onto the operators with another scaling dimension
$\Delta_e=1/2$. Even for a fairly particle-hole asymmetric case with the
Fermi-liquid ground state, the non-Fermi-liquid behavior has significant
influences in electric and thermal properties.


title: Two-terminal conductance fluctuations in the integer quantum Hall regime

abstract:
  Motivated by recent experiments on the conductance fluctuations in mesoscopic
integr quantum Hall systems, we consider a model in which the Coulomb
interactions are incorporated into the picture of edge-state transport through
a single saddle-point. The occupancies of `classical' localised states in the
two-dimensional electron system change due to the interactions between
electrons when the gate voltage on top of the device is varied. The
electrostatic potential between the localised states and the saddle-point
causes fluctuations of the saddle-point potential and thus fluctuations of the
transmission probability of edge states. This simple model is studied
numerically and compared with the observation.


title:
Topological Aspect of high-$T_c$ Superconductivity, Fractional Quantum
  Hall Effect and Berry Phase

abstract:
  We have analysed here the equivalence of RVB states with $\nu=1/2$ FQH states
in terms of the Berry Phase which is associated with the chiral anomaly in 3+1
dimensions. It is observed that the 3-dimensional spinons and holons are
characterised by the non-Abelian Berry phase and these reduce to 1/2 fractional
statistics when the motion is confined to the equatorial planes. The
topological mechanism of superconductivity is analogous to the topological
aspects of fractional quantum Hall effect with $\nu=1/2$.


title: Coherently Scattering Atoms from an Excited Bose-Einstein Condensate

abstract:
  We consider scattering atoms from a fully Bose-Einstein condensed gas. If we
take these atoms to be identical to those in the Bose-Einstein condensate, this
scattering process is to a large extent analogous to Andreev reflection from
the interface between a superconducting and a normal metal. We determine the
scattering wave function both in the absence and the presence of a vortex. Our
results show a qualitative difference between these two cases that can be
understood as due to an Aharonov-Bohm effect. It leads to the possibility to
experimentally detect and study vortices in this way.


title: Quantum Hall Transitions in Field Induced Spin Density Wave Systems

abstract:
  Field Induced Spin Density Wave (FISDW) systems exhibit coexistence phases
between well defined quantum Hall plateau phases with even integers 2N and 2N'.
We show that a disordered coexistence region accounts for the observed peaks in
the longitudinal resistivity as the field varies between plateaux. It also
results in a random spin mixing which yields two energy split extended states.
The longitudinal resistance is expected to show peaks witha temperature (T)
dependent width proportional to the kappa's power of T. The peak width should
saturate below the non-nesting interlayer coupling of order 40 mK


title: Quantum Theory for Mesoscopic Electric Circuits and Its Applications

abstract:
  This talk is assumed to exhibit an overview of the quantum theory for
mesoscopic electric circuits and some of its further developments. In the
theory the importance of the discreteness of electronic charge in mesoscopic
electric circuit is addressed. The mesoscopic LC-design is quantized in accord
with the charge discreteness. The uncertainty relation for electric charge and
current is given. Because the stationary Schr\"odinger equation is turned to be
Mathieu equation in $p$-representation, the wave function and energy spectrum
is formally solved. As further applications, the persistent current is obtained
by considering the mesoscopic ring as a pure L-design. The Coulomb blockade
phenomenon occurs when applying the theory to the pure C-design. Concerning the
time evolution of the states for mesoscopic electric circuit, we are able to
study it by the method of characteristics. In order to study the dissipative
effect in the circuit, we use density-matrix formulation. In this formulation,
several type of ``off diagonal'' dissipations are expected to be discussed.


title:
Heat transport and self-organized criticality in liquid 4He close to
  T_lambda

abstract:
  We present a renormalization-group calculation based on model F for the
thermal conductivity lambda_T(T,Q) in the presence of a homogeneous heat
current Q and gravity. For temperatures below T_lambda we obtain a large but
finite thermal conductivity corresponding to superfluid 4He with dissipation.
Furthermore, we consider the self-organized critical state where the effects of
gravity and heat current cancel each other so that the distance from
criticality delta T = T(z) - T_lambda(z) is constant in space and a function of
Q. We compare our theoretical results with recent experiments.


title: Magnetic reconstruction at (001) CaMnO$_3$ surface

abstract:
  The Mn-terminated (001) surface of the stable anti-ferromagnetic insulating
phase of cubic perovskite CaMnO$_3$ is found to undergo a magnetic
reconstruction consisting on a spin-flip process at surface: each Mn spin at
the surface flips to pair with that of Mn in the subsurface layer. In spite of
very little Mn-O charge transfer at surface, the surface behavior is driven by
the $e_g$ states due to $d_{xy}$ $\to$ $d_{z^2}$ charge redistribution. These
results, based on local spin density theory, give a double exchange like
coupling that is driven by $e_g$ character, not additional charge, and may have
relevance to CMR materials.