title: Glasses: a new view from QED coherence

abstract:
  Faced with the Kauzmann paradox, glasses have always been a puzzle for
condensed matter theorists. We show that in a new picture of condensed matter,
which takes into account the coherent interaction mechanisms of QED, glasses
are nothing but liquids, whose non coherent fraction is highly depleted, very
close to zero near T$_g$, the temperature of glass formation. Using the
recently developed QED theory of liquid water, we are also able to give a
successful account of the surprising finding of two low-temperature water
amorphs and of their phase-transition.


title:
Sound and Heat Absorption by a 2D Electron Gas in an Odd-Integer
  Quantized-Hall Regime

abstract:
  The absorption of bulk acoustic phonons in a two-dimensional (2D) GaAs/AlGaAs
heterostructure is studied (in the clean limit) where the 2D electron-gas
(2DEG), being in an odd-integer quantum-Hall state, is in fact a spin
dielectric. Of the two channels of phonon absorption associated with excitation
of spin waves, one, which is due to the spin-orbit (SO) coupling of electrons,
involves a change of the spin state of the system and the other does not. We
show that the phonon-absorption rate corresponding to the former channel (in
the paper designated as the second absorption channel) is finite at zero
temperature ($T$), whereas that corresponding to the latter (designated as the
first channel) vanishes for $T\to 0$. The long-wavelength limit, being the
special case of the first absorption channel, corresponds to sound (bulk and
surface) attenuation by the 2DEG. At the same time, the ballistic phonon
propagation and heat absorption are determined by both channels. The 2DEG
overheat and the attendant spin-state change are found under the conditions of
permanent nonequilibrium phonon pumping.


title: Delocalized Coulomb phase in two dimensions

abstract:
  Extending finite size scaling theory to the many body ground state, one finds
that Coulomb repulsion can drive a system of spinless fermions in a random
potential from the Anderson insulator (Fermi glass of localized states) towards
a new extended phase in dimension $d=2$. The transition occurs at a Coulomb
energy to Fermi energy ratio $r_s \approx 4$, where a change in the nature of
the persistent currents has been previously observed. Relevance to the recently
observed $2d$ metallic phase is suggested.


title: Non-fermi liquid as passive scalar fluid

abstract:
  I suggest that electron localization by random flux and passive transport in
quenched velocity fields in two dimensions be studied as perturbations of the
simple operator ${\cal K}={\bf A} \cdot \nabla$, with incompressible velocity
field/vector potential ${\bf A}=\nabla \times
\phi=(-\partial_y,\partial_x)\phi$. This operator has an infinitely degenerate
subspace of zero energy eigenstates, arising from incompressibility, that are
{\it extended} for generic $\phi({\bf x})$ and are expected to remain so under
perturbation. I propose that an anomaly accounts qualitatively for properties
of the spectrum and eigenstates of ${\cal K}$ and its perturbations.


title:
Magnetic field effects on two-leg Heisenberg antiferromagnetic ladders:
  Thermodynamic properties

abstract:
  Using the recently developed transfer-matrix renormalization group method, we
have studied the thermodynamic properties of two-leg antiferromagnetic ladders
in the magnetic field. Based on different behavior of magnetization, we found
disordered spin liquid, Luttinger liquid, spin-polarized phases and a classical
regime depending on magnetic field and temperature. Our calculations in
Luttinger liquid regime suggest that both the divergence of the NMR relaxation
rate and the anomalous specific heat behavior observed on
Cu$_2$(C$_5$H$_{12}$N$_2$)$_2$Cl$_4$}are due to quasi-one-dimensional effect
rather than three-dimensional ordering.


title: Phase Fluctuations and Non-Equilibrium Josephson Effect

abstract:
  We consider a diffusive S-N-S junction with electrons in the normal layer
driven out of equilibrium by external bias. We show that, the non-equilibrium
fluctuations of the electron density in the normal layer cause the fluctuations
of the phase of the order parameter in the S-layers. As a result, the magnitude
of the Josephson current in the non-equilibrium junction is significantly
supressed relative to its mean field value.


title: Ferromagnetism and superstructure in Ca_{1-x}La_xB_6

abstract:
  We critically investigate the model of a doped excitonic insulator, which
recently has been invoked to explain some experimental properties of the
ferromagnetic state in Ca_{1-x}La_xB_6. We demonstrate that the ground state of
this model is intrinsically unstable towards the appearance of a
superstructure. In addition, the model would lead to a phase separation regime
and the domain structure which may be prevented by the Coulomb forces only.
Recent experiments indicate that a superstructure may indeed show up in this
material.


title: Possible scenario of the melting of metals

abstract:
  A microscopic picture of the ``preparation'' of a crystal to the transition
to liquid state at the approach to melting temperature is proposed. Basing on
simple crystallogeometric considerations and the analysis of the computational
results for corresponding anharmonic characteristics an evaluation is given for
the magnitude of atomic displacements leading to the appearance of close packed
Bernal pseudonuclei in the solid phase. A physical meaning of the classical
Lindeman criterion and the mechanisms of the formation of free volume in the
crystal phase are discussed.


title:
Coexistence of the Critical Slowing Down and Glassy Freezing in Relaxor
  Ferroelectrics

abstract:
  We have developed a dynamical model for the dielectric response in relaxor
ferroelectrics which explicitly takes into account the coexistence of the
critical slowing down and glassy freezing. The application of the model to the
experiment in PMN allowed for the reconstruction of the nonequilibrium spin
glass state order parameter and its comparison with the results of recent NMR
experiment (Blinc et al., Phys. Rev. Lett. 83, No. 2 (1999)). It is shown that
the degree of the local freezing is rather small even at temperatures where the
field-cooled permittivity exceeds the frequency dependent permittivity by an
order of magnitude. This observation indicates the significant role of the
critical slowing down (accompanying the glass freezing) in the system dynamics.
Also the theory predicts an important interrelationship between the frequency
dependent permittivity and the zero-field-cooled permittivity, which proved to
be consistent with the experiment in PMN (A. Levstik et. al., Phys. Rev. B 57,
11204 (1998)).


title:
Deviation from Maxwell Distribution in Granular Gases with Constant
  Restitution Coefficient

abstract:
  We analyze the velocity distribution function of force-free granular gases in
the regime of homogeneous cooling when deviations from the Maxwellian
distribution may be accounted only by leading term in the Sonine polynomial
expansion. These are quantified by the magnitude of the coefficient $a_2$ of
the second term of the expansion. In our study we go beyond the linear
approximation for $a_2$ and observe that there are three different values
(three roots) for this coefficient which correspond to a scaling solution to
the Boltzmann equation. The stability analysis performed showed, however, that
among these three roots only one corresponds to a stable scaling solution. This
is very close to $a_2$, obtained in previous studies in a linear with respect
to $a_2$ approximation.


title:
Stability of a fixed point in the replica action for the random field
  Ising model

abstract:
  We reconsider stability of the non-trivial fixed point in $6-\epsilon $
dimensional effective action for the random field Ising model derived by
Br\'{e}zin and De Dominicis. After expansion parameters of physical observables
are clarified, we find that the non-trivial fixed point in $6-\epsilon$
dimensions is stable, contrary to the argument by Br\'{e}zin and De Dominicis.
We also computed the exponents $\nu$ and $\eta$ by the $\epsilon$ expansion.
The results are consistent with the argument of the dimensional reduction at
least in the leading order.


title:
Conductance Quantization and Magnetoresistance in Magnetic Point
  Contacts

abstract:
  We theoretically study the electron transport through a magnetic point
contact (PC) with special attention to the effect of an atomic scale domain
wall (DW). The spin precession of a conduction electron is forbidden in such an
atomic scale DW and the sequence of quantized conductances depends on the
relative orientation of magnetizations between left and right electrodes. The
magnetoresistance is strongly enhanced for the narrow PC and oscillates with
the conductance.


title:
Phase fluctuations and Non-Fermi Liquid Properties of 2D Fermi-system
  with attraction

abstract:
  The effect of static fluctuations in the phase of the order parameter on the
normal and superconducting properties of a 2D system with attractive
four-fermion interaction has been studied. Analytic expressions for the fermion
Green function, its spectral density and the density of states are derived. The
resultant single-particle Green function clearly demonstrates non-Fermi liquid
behavior. The results show that as the temperature increases through the 2D
critical temperature the width of the quasiparticle peaks broadens
significantly. At the same time one retains the gap in quasiparticle spectrum.
The spectral density for the dynamical fluctuations can also be obtained.
Clearly the dynamical fluctuations fill the gap giving the observed pseudogap
behaviour.


title: Noise effects for the Depolarizing Channel

abstract:
  The possibility of stochastic resonance of a quantum channel and hence the
noise enhanced capacity of the channel is explored by considering the
depolarizing channel. The fidelity of the channel is also considered. Although
there is no clear evidence for noise enhanced capacity found, there is
enhancement for the fidelity for the depolarizing channel. PACS number(s):
05.40.-a, 03.67.Hk


title: Boundary Kondo impurities in the generalized supersymmetric t-J model

abstract:
  We study the generalized supersymmetric t-J model with Kondo impurities in
the boundaries. We first construct the higher spin operator K-matrix for the
XXZ Heisenberg chain. Setting the boundary parameter to be a special value, we
find a higher spin reflecting K-matrix for the supersymmetric t-J model. By
using the Quantum Inverse Scattering Method, we obtain the eigenvalue and the
corresponding Bethe ansatz equations.


title:
Magnetoresistance of magnetic multilayers in the CPP mode:evidence for
  non-local scattering

abstract:
  We have carried out measurements of the magnetoresistance MR(H) in the CPP
(Current Perpendicular to the Plane) mode for two types of magnetic multilayers
which have different layer ordering. The series resistor model predicts that
CPP MR(H) is independent of the ordering of the layers. Nevertheless, the
measured MR(H) curves were found to be completely different for the following
two configurations:[Co(1nm)/Cu(20nm)/Co(6nm)/Cu(20nm)]*N and
[Co(1nm)/Cu(20nm)]*N[Co(6nm)/Cu(20nm)]*N showing that the above model is
incorrect. We have carried out a calculation showing that these results can be
explained quantitatively in terms of the non-local character of the electron
scattering, without the need to invoke spin-flip scattering or a short spin
diffusion length.


title:
The validity of the Landau-Zener model for output coupling of Bose
  condensates

abstract:
  We investigate the validity of the Landau-Zener model in describing the
output coupling of Bose condensates from magnetic traps by a chirped
radiofrequency field. The predictions of the model are compared with the
numerical solutions of the Gross-Pitaevskii equation. We find a dependence on
the chirp direction, and also quantify the role of gravitation.


title:
Metallic surface of a Mott insulator - Mott insulating surface of a
  metal

abstract:
  The dynamical mean-field theory (DMFT) is employed to study the Mott
transition in the semi-infinite Hubbard model at half-filling and zero
temperature. We consider the low-index surfaces of the three-dimensional
simple-cubic lattice and systematically vary the model parameters at the very
surface. Within the DMFT the problem is self-consistently mapped onto a set of
coupled effective impurity models corresponding to the inequivalent layers
parallel to the surface. Assuming that the influence of the Hubbard bands on
the low-energy quasi-particle resonance can be neglected at the critical point,
a simplified ``linearized DMFT'' becomes possible which is formally equivalent
to the Weiss molecular-field theory for the semi-infinite Ising model. This
implies that qualitatively the rich phenomenology of the Landau description of
second-order phase transitions at surfaces has a direct analogue for the
surface Mott transition. Motivated by this formal analogy, we work out the
predictions of the linearized DMFT in detail. It is found that under certain
circumstances the surface of a Mott insulator can be metallic while a
Mott-insulating surface of a normal metal is not possible. The corresponding
phase diagrams, the (mean-field) critical exponents and the critical profiles
of the quasi-particle weight are derived. The results are confirmed by a fully
numerical evaluation of the DMFT equations using the exact-diagonalization (ED)
method.


title: Heteroskedastic Levy Flights

abstract:
  Truncated L\'{e}vy flights are random walks in which the arbitrarily large
steps of a L\'{e}vy flight are eliminated. Since this makes the variance
finite, the central limit theorem applies, and as time increases the
probability distribution of the increments becomes Gaussian. Here, truncated
L\'{e}vy flights with correlated fluctuations of the variance
(heteroskedasticity) are considered. What makes these processes interesting is
the fact that the crossover to the Gaussian regime may occur for times
considerably larger than for uncorrelated (or no) variance fluctuations. These
processes may find direct application in the modeling of some economic time
series.


title: Perturbation Expansion in Phase-Ordering Kinetics: II. N-vector Model

abstract:
  The perturbation theory expansion presented earlier to describe the
phase-ordering kinetics in the case of a nonconserved scalar order parameter is
generalized to the case of the $n$-vector model. At lowest order in this
expansion, as in the scalar case, one obtains the theory due to Ohta, Jasnow
and Kawasaki (OJK). The second-order corrections for the nonequilibrium
exponents are worked out explicitly in $d$ dimensions and as a function of the
number of components $n$ of the order parameter. In the formulation developed
here the corrections to the OJK results are found to go to zero in the large
$n$ and $d$ limits. Indeed, the large-$d$ convergence is exponential.


title:
Internal and interfacial friction in the dynamics of soft/solid
  interfaces

abstract:
  We analyze theoretically the effect of friction on quartz crystal
microbalance (QCM) measurements that probe soft (viscoelastic) films and
biomolecular layers adsorbed from aqueous solutions. While water provides a
natural environment for biomolecules, an interface with unknown rheological
properties forms between the adsorbed soft molecular layer and the quartz
substrate in the latter case. We investigate therefore the dynamics of soft
films adsorbed onto a solid quartz surface within a continuum mechanics
approach using both the Maxwell and the Voight/Kelvin models of viscoelasticity
and their combination. The rigorous expressions derived for the acoustic
response of a quartz crystal oscillator, accounting for both interfacial
(sliding) friction and internal friction (viscosity), demonstrate that the QCM
can be used as a sensor for quantitative characteristization of friction
effects as well as for ``in situ'' measurements of mechanical properties of
adsorbed biomolecular films.


title:
Scattering on spin fluctuations in itinerant quantum disordered
  ferromagnets near quantum phase transition

abstract:
  Taking into account the long-ranged spin interactions due to weak
localization effects in disordered itinerant ferromagnets the scattering of
both electrons and neutrons on critical spin fluctuations near quantum phase
transition is considered. It is shown that for the case of low electron
density, when k_F \xi \ll 1, where k_F is the Fermi momentum and \xi is the
magnetic correlation length, the transport cross section of electrons is
proportional to conventional critical fluctuations in absence of weak
localization effects. However, the intensity of the multiple small-angle
neutron scattering becomes exponentially small as compared with the intensity
of the multiple scattering by conventional critical fluctuations.


title:
Topological Invariants in Microscopic Transport on Rough Landscapes:
  Morphology, Hierarchical Structure, and Horton Analysis of Riverlike Networks
  of Vortices

abstract:
  River basins as diverse as the Nile, the Amazon, and the Mississippi satisfy
certain topological invariants known as Horton's laws. Do these macroscopic (up
to 10^3 km) laws extend to the micron scale? Through realistic simulations, we
analyze the morphology and statistical properties of networks of vortex flow in
flux-gradient-driven superconductors. We derive a phase diagram of the
different network morphologies, including one in which Horton's laws of length
and stream number are obeyed -- even though these networks are about 10^9 to
10^15 times smaller than geophysical river basins.


title:
Theory of Pseudogap Phenomena in High-Tc Cuprates Based on the Strong
  Coupling Superconductivity

abstract:
  In this paper we study the effects of the strong coupling superconductivity
on the normal state electronic structure. We point out that the pseudogap
phenomena in High-T_c cuprates are naturally explained as a precursor of the
strong coupling superconductivity.
  We expand the reciprocal of the T-matrix with respect to the momentum and the
frequency, and we discuss the properties of the expansion parameters. We
estimate these parameters and carry out the calculations for the single
particle self-energy using the T-matrix and the self-consistent T-matrix
approximations, respectively.
  We show that the superconducting fluctuations, which are strongly diffusive
within the conventional weak coupling theory, become propagative and have the
character of the pre-formed pairs in the strong coupling case.
  The spectral weight and the density of states show the gap-like features by
the effects of the resonances with the thermally excited weakly-damped
pre-formed pairs.
  The spectral weight at the Fermi energy is strongly suppressed.
  This suppression starts at the mean field critical temperature $T_{MF}$ and
the actual critical temperature T_c is strongly reduced owing to the
fluctuations.
  These features properly explain to the pseudogap phenomena in High-T_c
cuprates.


title: Optical response of supported particles

abstract:
  The present work reports a general method for the calculation of t he
polarizability of a truncated sphere on a substrate. A multipole ex pansion is
used, where the multipoles are not necessarily localized in the center of the
sphere but can freely move on the revolution axis. From the weak formulation of
the boundary conditions, an infinite set of linear equations for the multipole
coefficients is derived. To obta in this set, the interaction between the
island and the substrate is t aken into account by the technique of image
multipoles. For numerical implementation, this set is truncated at an arbitrary
mu ltipole order. The accuracy of the method is jugded through the stabil ity
of the truncated sphere polarizability and the the fulfilment of t he boundary
conditions which are demonstrated to be satisfied in large regions of the
parameter space. This method brings an improvement wit h respect to the
Bedeaux's case \cite{Wind87a,Wind87b} where the multi poles are located in the
center of the sphere.


title: Phase-ordering dynamics of the Gay-Berne nematic liquid crystal

abstract:
  Phase-ordering dynamics in nematic liquid crystals has been the subject of
much active investigation in recent years in theory, experiments and
simulations. With a rapid quench from the isotropic to nematic phase a large
number of topological defects are formed and dominate the subsequent
equilibration process. We present here the results of a molecular dynamics
simulation of the Gay-Berne model of liquid crystals after such a quench in a
system with 65536 molecules. Twist disclination lines as well as type-1 lines
and monopoles were observed. Evidence of dynamical scaling was found in the
behavior of the spatial correlation function and the density of disclination
lines. However, the behavior of the structure factor provides a more sensitive
measure of scaling, and we observed a crossover from a defect dominated regime
at small values of the wavevector to a thermal fluctuation dominated regime at
large wavevector.


title: Magnetic susceptibility of diluted pyrochlore and SCGO antiferromagnets

abstract:
  We investigate the magnetic susceptibility of the classical Heisenberg
antiferromagnet with nearest-neighbour interactions on the geometrically
frustrated pyrochlore lattice, for a pure system and in the presence of
dilution with nonmagnetic ions. Using the fact that the correlation length in
this system for small dilution is always short, we obtain an approximate but
accurate expression for the magnetic susceptibility at all temperatures. We
extend this theory to the compound SrCr_{9-9x}Ga_{3+9x}O_{19} (SCGO) and
provide an explanation of the phenomenological model recently proposed by
Schiffer and Daruka [Phys. Rev. B56, 13712 (1997)].


title:
Simulation of I-V Hysteresis Branches in An Intrinsic Stack of Josephson
  Junctions in High $T_c$ Superconductors

abstract:
  I-V characteristics of the high T$_c$ superconductor
Bi$_2$Sr$_2$Ca$_1$C$_2$O$_8$ shows a strong hysteresis, producing many
branches. The origin of hysteresis jumps is studied by use of the model of
multi-layered Josephson junctions proposed by one of the authors (T. K.). The
charging effect at superconducting layers produces a coupling between the next
nearest neighbor phase-differences, which determines the structure of
hysteresis branches. It will be shown that a solution of phase motions is
understood as a combination of rotating and oscillating phase-differences, and
that, at points of hysteresis jumps, there occurs a change in the number of
rotating phase-differences. Effects of dissipation are analyzed. The
dissipation in insulating layers works to damp the phase motion itself, while
the dissipation in superconducting layers works to damp relative motions of
phase-differences. Their effects to hysteresis jumps are discussed.


title: Microscopic expressions for the thermodynamic temperature

abstract:
  We show that arbitrary phase space vector fields can be used to generate
phase functions whose ensemble averages give the thermodynamic temperature. We
describe conditions for the validity of these functions in periodic boundary
systems and the Molecular Dynamics (MD) ensemble, and test them with a
short-ranged potential MD simulation.


title:
van der Waals interaction in nanotube bundles : consequences on
  vibrational modes

abstract:
  We have developed a pair-potential approach for the evaluation of van der
Waals interaction between carbon nanotubes in bundles.
  Starting from a continuum model, we show that the intertube modes range from
$5 cm^{-1}$ to $60 cm^{-1}$. Using a non-orthogonal tight-binding approximation
for describing the covalent intra-tube bonding in addition, we confirme a
slight chiral dependance of the breathing mode frequency and we found that this
breathing mode frequency increase by $\sim$ 10 % if the nanotube lie inside a
bundle as compared to the isolated tube.


title:
Metal-Insulator Transition and Spin Degree of Freedom in Silicon 2D
  Electron Systems

abstract:
  Magnetotransport in 2DES's formed in Si-MOSFET's and Si/SiGe quantum wells at
low temperatures is reported. Metallic temperature dependence of resistivity is
observed for the n-Si/SiGe sample even in a parallel magnetic field of 9T,
where the spins of electrons are expected to be polarized completely.
Correlation between the spin polarization and minima in the diagonal
resistivity observed by rotating the samples for various total strength of the
magnetic field is also investigated.


title:
Local magnetic structure due to inhomogeneity of interaction in S=1/2
  antiferromagnetic chain

abstract:
  We study the magnetic properties of $S=1/2$ antiferromagnetic Heisenberg
chains with inhomogeneity of interaction. Using a quantum Monte Carlo method
and an exact diagonalization method, we study bond-impurity effect in the
uniform $S=1/2$ chain and also in the bond-alternating chain. Here `bond
impurity' means a bond with strength different from those in the bulk or a
defect in the alternating order. Local magnetic structures induced by bond
impurities are investigated both in the ground state and at finite
temperatures, calculating the local magnetization, the local susceptibility and
the local field susceptibility. We also investigate the force acting between
bond impurities and find the force generally attractive.


title: Damage-Spreading in Self-Organized Critical Systems

abstract:
  We study the behavior under perturbations of different versions of
Bak-Sneppen (BS) model in 1 + 1 dimension. We focus our attention on the
damage-spreading features of the BS model with both random as well as
deterministic updating, with sequential as well as parallel updating.
  In addition, we compute analytically the asymptotic plateau reached by the
distance after the growing phase.


title:
From Car Parking to Protein Adsorption: An Overview of Sequential
  Adsorption Processes

abstract:
  The adsorption or adhesion of large particles (proteins, colloids, cells,
>...) at the liquid-solid interface plays an important role in many diverse
applications. Despite the apparent complexity of the process, two features are
particularly important: 1) the adsorption is often irreversible on experimental
time scales and 2) the adsorption rate is limited by geometric blockage from
previously adsorbed particles. A coarse-grained description that encompasses
these two properties is provided by sequential adsorption models whose simplest
example is the random sequential adsorption (RSA) process. In this article, we
review the theoretical formalism and tools that allow the systematic study of
kinetic and structural aspects of these sequential adsorption models. We also
show how the reference RSA model may be generalized to account for a variety of
experimental features including particle anisotropy, polydispersity, bulk
diffusive transport, gravitational effects, surface-induced conformational and
orientational change, desorption, and multilayer formation. In all cases, the
significant theoretical results are presented and their accuracy (compared to
computer simulation) and applicability (compared to experiment) are discussed.


title: Enhanced Saturation Coverages in Adsorption-Desorption Processes

abstract:
  Many experimental studies of protein deposition on solid surfaces involve
alternating adsorption/desorption steps. In this paper, we investigate the
effect of a desorption step (separating two adsorption steps) on the kinetics,
the adsorbed-layer structure, and the saturation density. Our theoretical
approach involves a density expansion of the pair distribution function and an
application of an interpolation formula to estimate the saturation density as a
function of the density at which the desorption process commences, $\rho_1$,
and the density of the depleted configuration, $\rho_2$. The theory predicts an
enhancement of the saturation density compared with that of a simple,
uninterrupted RSA process and a maximum in the saturation density when
$\rho_2={2/3}\rho_1$. The theoretical results are in qualitative and in
semi-quantitative agreement with the results of numerical simulations.


title: Macroscopic Dynamics of Multi-Lane Traffic

abstract:
  We present a macroscopic model of mixed multi-lane freeway traffic that can
be easily calibrated to empirical traffic data, as is shown for Dutch highway
data. The model is derived from a gas-kinetic level of description, including
effects of vehicular space requirements and velocity correlations between
successive vehicles. We also give a derivation of the lane-changing rates. The
resulting dynamic velocity equations contain non-local and anisotropic
interaction terms which allow a robust and efficient numerical simulation of
multi-lane traffic. As demonstrated by various examples, this facilitates the
investigation of synchronization patterns among lanes and effects of on-ramps,
off-ramps, lane closures, or accidents.


title:
Friedel phases and phases of transmission amplitudes in quantum
  scattering systems

abstract:
  We illustrate the relation between the scattering phase appearing in the
Friedel sum rule and the phase of the transmission amplitude for quantum
scatterers connected to two one-dimensional leads. Transmission zero points
cause abrupt phase changes $\pm\pi$ of the phase of the transmission amplitude.
In contrast the Friedel phase is a continuous function of energy. We
investigate these scattering phases for simple scattering problems and
illustrate the behavior of these models by following the path of the
transmission amplitude in the complex plane as a function of energy. We verify
the Friedel sum rule for these models by direct calculation of the scattering
phases and by direct calculation of the density of states.


title: Plane dimpling and Cu 4s hybridization in YBa_2Cu_3O_x

abstract:
  Oxygen doping dimples the CuO_2 planes of YBa_2Cu_3O_{6.8-6.92} by displacing
copper normal to the planes and further towards Ba. The correlated oxygen
displacements, however, are constrained to the in-plane axes. This displacement
pattern is discussed in terms of doping dependent Cu 4s - 3d hybridizations.


title:
Quantitative Model of Large Magnetostrain Effect in Ferromagnetic Shape
  Memory Alloys

abstract:
  A quantitative model describing large magnetostrain effect observed in
several ferromagnetic shape memory alloys such as Ni2MnGa is briefly
reported.The paper contains an exact thermodynamic consideration of the
mechanical and magnetic properties for a similar type materials. As a result,
the basic mechanical state equation including magnetic field effect is directly
derived from a general Poisson's rule. It is shown that the magnetic field
induced deformation effect is directly connected with the strain dependence of
magnetization. A simple model of magnetization and its dependence on the strain
is considered and applied to explain the results of experimental study of large
magnetostrain effects in Ni2MnGa.


title: Self-Organized Percolation Model for Stock Market Fluctuations

abstract:
  In the Cont-Bouchaud model [cond-mat/9712318] of stock markets, percolation
clusters act as buying or selling investors and their statistics controls that
of the price variations. Rather than fixing the concentration controlling each
cluster connectivity artificially at or close to the critical value, we propose
that clusters shatter and aggregate continuously as the concentration evolves
randomly, reflecting the incessant time evolution of groups of opinions and
market moods. By the mechanism of ``sweeping of an instability'' [D. Sornette,
Journal de Physique I 4, 209 (1994)], this market model spontaneously exhibits
reasonable power law statistics for the distribution of price changes and
accounts for the other important stylized facts of stock market price
fluctuations.


title:
Analysis of the phenomenon of speculative trading in one of its basic
  manifestations: postage stamp bubbles

abstract:
  We document and analyze the empirical facts concerning one of the clearest
evidence of speculation in financial trading as observed in the postage
collection stamp market. We unravel some of the mechanisms of speculative
behavior which emphasize the role of fancy and collective behavior. In our
conclusion, we propose a classification of speculative markets based on two
parameters, namely the amplitude of the price peak and a second parameter that
measures its ``sharpness''. This study is offered to anchor modeling efforts to
realistic market constraints and observations.


title: Pattern selection in a lattice of pulse-coupled oscillators

abstract:
  We study spatio-temporal pattern formation in a ring of N oscillators with
inhibitory unidirectional pulselike interactions. The attractors of the
dynamics are limit cycles where each oscillator fires once and only once. Since
some of these limit cycles lead to the same pattern, we introduce the concept
of pattern degeneracy to take it into account. Moreover, we give a qualitative
estimation of the volume of the basin of attraction of each pattern by means of
some probabilistic arguments and pattern degeneracy, and show how are they
modified as we change the value of the coupling strength. In the limit of small
coupling, our estimative formula gives a perfect agreement with numerical
simulations.


title: The formation of a non-magnetic state for the d6 electronic system

abstract:
  It has been shown that the crystal-field interactions can produce a non-
magnetic singlet ground state for the highly-correlated d6 system situated in
the quasi-octahedral crystal field (CEF) surrounding provided the spin-orbit
interactions are correctly taking into account. The spin-orbit interactions in
combination with the trigonal distortion of the cubic CEF interactions produce
a peculiar energy level scheme with a non-magnetic ground state and highly-
magnetic excited states at 11 and 70 meV. The calculated temperature dependence
of the magnetic susceptibility exhibits very substantial departure from the
Curie law that is due to second-order CEF interactions. The present
considerations can be applied to Co3+ and Fe2+- ion compounds. The derived
electronic and magnetic properties mimic very much those found experimentally
for LaCoO3.


title: Enhanced Pulse Propagation in Non-Linear Arrays of Oscillators

abstract:
  The propagation of a pulse in a nonlinear array of oscillators is influenced
by the nature of the array and by its coupling to a thermal environment. For
example, in some arrays a pulse can be speeded up while in others a pulse can
be slowed down by raising the temperature. We begin by showing that an energy
pulse (1D) or energy front (2D) travels more rapidly and remains more localized
over greater distances in an isolated array (microcanonical) of hard springs
than in a harmonic array or in a soft-springed array. Increasing the pulse
amplitude causes it to speed up in a hard chain, leaves the pulse speed
unchanged in a harmonic system, and slows down the pulse in a soft chain.
Connection of each site to a thermal environment (canonical) affects these
results very differently in each type of array. In a hard chain the dissipative
forces slow down the pulse while raising the temperature speeds it up. In a
soft chain the opposite occurs: the dissipative forces actually speed up the
pulse while raising the temperature slows it down. In a harmonic chain neither
dissipation nor temperature changes affect the pulse speed. These and other
results are explained on the basis of the frequency vs energy relations in the
various arrays.


title: Density matrix purification due to continuous quantum measurement

abstract:
  We consider the continuous quantum measurement of a two-level system, for
example, a single-Cooper-pair box measured by a single-electron transistor or a
double-quantum dot measured by a quantum point contact. While the approach most
commonly used describes the gradual decoherence of the system due to the
measurement, we show that when taking into account the detector output, we get
the opposite effect: gradual purification of the density matrix. The
competition between purification due to measurement and decoherence due to
interaction with the environment can be described by a simple Langevin equation
which couples the random evolution of the system density matrix and the
stochastic detector output. The gradual density matrix purification due to
continuous measurement may be verified experimentally using present-day
technology. The effect can be useful for quantum computing.


title: Scattering theory of the Johnson spin transistor

abstract:
  We discuss a simple, semiclassical scattering theory for spin-dependent
transport in a many-terminal formulation, with special attention to the four
terminal device of Johnson referred to as spin transistor


title: Finite temperature transport in integrable quantum many body systems

abstract:
  Recent developments in the analysis of finite temperature dissipationless
transport in integrable quantum many body problems are presented. In
particular, we will discuss: (i) the role played by the conservation laws in
systems as the spin 1/2 Heisenberg chain and the one-dimensional Hubbard model,
(ii) exact results obtained using the Bethe ansatz method on the long time
decay of current correlations.


title: Multishelled Gold Nanowires

abstract:
  The current miniaturization of electronic devices raises many questions about
the properties of various materials at nanometre-scales. Recent molecular
dynamics computer simulations have shown that small finite nanowires of gold
exist as multishelled structures of lasting stability. These classical
simulations are based on a well-tested embedded atom potential. Molecular
dynamics simulation studies of metallic nanowires should help in developing
methods for their fabrication, such as electron-beam litography and scanning
tunneling microscopy.


title: Fractal Growth with Quenched Disorder

abstract:
  In this lecture we present an overview of the physics of irreversible fractal
growth process, with particular emphasis on a class of models characterized by
{\em quenched disorder}.
  These models exhibit self-organization, with critical properties developing
spontaneously, without the fine tuning of external parameters. This situation
is different from the usual critical phenomena, and requires the introduction
of new theoretical methods. Our approach to these problems is based on two
concepts, the Fixed Scale Transformation, and the quenched-stochastic
transformation, or Run Time Statistics (RTS), which maps a dynamics with
quenched disorder into a stochastic process. These methods, combined together,
allow us to understand the self-organized nature of models with quenched
disorder and to compute analytically their critical exponents. In addition, it
is also possible characterize mathematically the origin of the dynamics by {\em
avalanches} and compare it with the {\em continuous growth} of other fractal
models. A specific application to Invasion Percolation will be discussed. Some
possible relations to glasses will also be mentioned.


title: Magnetic Interaction in Insulating Cuprates

abstract:
  We examine two-spin (2S) and cyclic four-spin (4S) magnetic interactions in
insulating ladder and two-dimensional (2D) cuprates. By a comparison of
eigenstates between d-p and Heisenberg models, we evaluate magnitudes of these
interactions. We find that the 4S interaction is $\sim$10% of nearest
neighboring 2S interaction, and a diagonal 2S interaction is considerably
small. The 4S interaction for a ladder cuprate is larger than that for 2D one,
and plays an important role in the low-energy excitation. The Heisenberg ladder
with the obtained 2S and 4S interactions reproduces very well the experimental
result of the temperature dependence of the magnetic susceptibility.


title: Structure, Stresses and Local Dynamics in Glasses

abstract:
  The interrelations between short range structural and elastic aspects in
glasses and glass forming liquids pose important and yet unresolved questions.
In this paper these relations are analyzed for mono-atomic glasses and stressed
liquids with a short range repulsive-attractive pair potentials. Strong
variations of the local pressure are found even in a zero temperature glass,
whereas the largest values of pressure are the same in both glasses and
liquids. The coordination number z(J) and the effective first peak radius
depend on the local pressures J's. A linear relation was found between
components of site stress tensor and the local elastic constants. A linear
relation was also found between the trace of the squares of the local
frequencies and the local pressures. Those relations hold for glasses at zero
temperature and for liquids. We explain this by a relation between the
structure and the potential terms. A structural similarity between liquids and
solids is manifested by similar dependencies of the coordination number on the
pressures.


title: Pseudogap and Superconducting Gap in Y-123: A Raman Study

abstract:
  We present results of electronic Raman-scattering experiments in differently
doped Y-123. In B2g symmetry, an analysis of the data in terms of a memory
function approach is presented and dynamical relaxation rates
$\Gamma(\omega,T)$ and mass-enhancement factors $1+\lambda(\omega,T)$ for the
carriers are obtained. Starting from temperatures T > 180K, $\Gamma(\omega,T)$
and $1+\lambda(\omega,T)$ are extrapolated to lower temperatures and used to
re-calculate Raman spectra. By comparison with our data, we find a loss of
spectral weight between Tc < T < T* at all doping levels x. T* is comparable to
the pseudogap temperature found in other experiments. Below Tc, the
superconducting gap is observed. It depends on x and scales with Tc whereas the
energy scale of the pseudogap remains the same.


title: An Exactly Solvable Two-Way Traffic Model With Ordered Sequential Update

abstract:
  Within the formalism of matrix product ansatz, we study a two-species
asymmetric exclusion process with backward and forward site-ordered sequential
update. This model, which was originally introduced with the random sequential
update, describes a two-way traffic flow with a dynamic impurity and shows a
phase transition between the free flow and traffic jam. We investigate the
characteristics of this jamming and examine similarities and differences
between our results and those with random sequential update.


title: Superconducting Gap and Pseudogap in Bi-2212

abstract:
  We present results of Raman scattering experiments in differently doped
Bi-2212 single crystals. Below Tc the spectra show pair-breaking features in
the whole doping range. The low frequency power laws confirm the existence of a
$d_{x^2-y^2}$-wave order parameter. In the normal state between Tc and T* =
200K we find evidence for a pseudogap in B2g symmetry. Upon doping its effect
on the spectra decreases while its energy scale appears to be unchanged.


title:
Melting and Dimensionality of the Vortex Lattice in Underdoped
  YBa2Cu3O6.60

abstract:
  Muon spin rotation measurements of the magnetic field distribution in the
vortex state of the oxygen deficient high-Tc superconductor YBa{2}Cu{3}O{6.60}
reveal a vortex-lattice melting transition at much lower temperature than that
in the fully oxygenated material. The transition is best described by a model
in which adjacent layers of ``pancake'' vortices decouple in the liquid phase.
Evidence is also found for a pinning-induced crossover from a solid 3D to
quasi-2D vortex lattice, similar to that observed in the highly anisotropic
superconductor Bi{2+x}Sr{2-x}CaCu{2}O{8+y}.


title: Quantum Hall effect at low magnetic fields

abstract:
  The temperature and scale dependence of resistivities in the standard scaling
theory of the integer quantum Hall effect is discussed. It is shown that recent
experiments, claiming to observe a discrepancy with the global phase diagram of
the quantum Hall effect, are in fact in agreement with the standard theory. The
apparent low-field transition observed in the experiments is identified as a
crossover due to weak localization and a strong reduction of the conductivity
when Landau quantization becomes dominant.


title: Directed random walk in adsorbed monolayer

abstract:
  We study the dynamics of a tracer particle, which performs a totally directed
random walk in an adsorbed monolayer composed of mobile hard-core particles
undergoing continuous exchanges with a vapour phase. In terms of a
mean-field-type approach, based on the decoupling of the
tracer-particle-particle correlation functions into the product of pairwise,
tracer-particle correlations, we determine the density profiles of the
monolayer particles, as seen from the stationary moving tracer, and calculate
its terminal velocity, V_{tr}. In the general case the latter is determined
implicitly, as the solution of a certain transcendental equation. In two
extreme limits of slow and fast monolayer particles diffusion, we obtain
explicit asymptotic forms of V_{tr}. We show next that the density profile in
the monolayer is strongly inhomogeneous: In front of the stationary moving
tracer the local density is higher than the average value, \rho_L, and
approaches \rho_L as an exponential function of the distance from the tracer.
Past the tracer the local density is lower than \rho_L and the approach to
\rho_L may proceed differently depending whether the particles number in the
monolayer is not or is explicitly conserved. In the former case the approach is
described by an exponential dependence with a different characteristic length,
compared to the behavior in front of the tracer; in the latter case, the
density tends to \rho_L algebraically. The characteristic lengths and the
amplitudes of the density relaxation functions are also determined explicitly


title:
Field Induced Reduction of the Low Temperature Superfluid Density in
  YBa2Cu3O6.95

abstract:
  A novel high magnetic field (8 T) spectrometer for muon spin rotation has
been used to measure the temperature dependence of the in-plane magnetic
penetration depth in YBa2Cu3O6.95. At low H and low T, the penetration depth
exhibits the characteristic linear T dependence associated with the energy gap
of a d_x^2-y^2-wave superconductor. However, at higher fields the penetration
depth is essentially temperature independent at low T. We discuss possible
interpretations of this surprising new feature in the low-energy excitation
spectrum.


title:
Paired states of fermions in two dimensions with breaking of parity and
  time-reversal symmetries, and the fractional quantum Hall effect

abstract:
  We analyze pairing of fermions in two dimensions for fully-gapped cases with
broken parity (P) and time-reversal (T), especially cases in which the gap
function is an orbital angular momentum ($l$) eigenstate, in particular $l=-1$
(p-wave, spinless or spin-triplet) and $l=-2$ (d-wave, spin-singlet). For
$l\neq0$, these fall into two phases, weak and strong pairing, which may be
distinguished topologically. In the cases with conserved spin, we derive
explicitly the Hall conductivity for spin as the corresponding topological
invariant. For the spinless p-wave case, the weak-pairing phase has a pair
wavefunction that is asympototically the same as that in the Moore-Read
(Pfaffian) quantum Hall state, and we argue that its other properties (edge
states, quasihole and toroidal ground states) are also the same, indicating
that nonabelian statistics is a {\em generic} property of such a paired phase.
The strong-pairing phase is an abelian state, and the transition between the
two phases involves a bulk Majorana fermion, the mass of which changes sign at
the transition. For the d-wave case, we argue that the Haldane-Rezayi state is
not the generic behavior of a phase but describes the asymptotics at the
critical point between weak and strong pairing, and has gapless fermion
excitations in the bulk. In this case the weak-pairing phase is an abelian
phase which has been considered previously. In the p-wave case with an unbroken
U(1) symmetry, which can be applied to the double layer quantum Hall problem,
the weak-pairing phase has the properties of the 331 state, and with nonzero
tunneling there is a transition to the Moore-Read phase. The effects of
disorder on noninteracting quasiparticles are considered.


title:
Short-Range Interactions and Scaling Near Integer Quantum Hall
  Transitions

abstract:
  We study the influence of short-range electron-electron interactions on
scaling behavior near the integer quantum Hall plateau transitions. Short-range
interactions are known to be irrelevant at the renormalization group fixed
point which represents the transition in the non-interacting system. We find,
nevertheless, that transport properties change discontinuously when
interactions are introduced. Most importantly, in the thermodynamic limit the
conductivity at finite temperature is zero without interactions, but non-zero
in the presence of arbitrarily weak interactions. In addition, scaling as a
function of frequency, $\omega$, and temperature, $T$, is determined by the
scaling variable $\omega/T^p$ (where $p$ is the exponent for the temperature
dependence of the inelastic scattering rate) and not by $\omega/T$, as it would
be at a conventional quantum phase transition described by an interacting fixed
point. We express the inelastic exponent, $p$, and the thermal exponent, $z_T$,
in terms of the scaling dimension, $-\alpha < 0$, of the interaction strength
and the dynamical exponent $z$ (which has the value $z=2$), obtaining
$p=1+2\alpha/z$ and $z_T=2/p$.


title: Precise Critical Exponents for the Basic Contact Process

abstract:
  We calculated some of the critical exponents of the directed percolation
universality class through exact numerical diagonalisations of the master
operator of the one-dimensional basic contact process. Perusal of the power
method together with finite-size scaling allowed us to achieve a high degree of
accuracy in our estimates with relatively little computational effort. A simple
reasoning leading to the appropriate choice of the microscopic time scale for
time-dependent simulations of Markov chains within the so called quantum chain
formulation is discussed. Our approach is applicable to any stochastic process
with a finite number of absorbing states.


title: Spin gap and magnetic coherence in a clean high-T_c superconductor

abstract:
  A notable aspect of high-temperature superconductivity in the copper oxides
is the unconventional nature of the underlying paired-electron state. A direct
manifestation of the unconventional state is a pairing energy - that is, the
energy required to remove one electron from the superconductor - that varies
(between zero and a maximum value) as a function of momentum or wavevector: the
pairing energy for conventional superconductors is wavevector-independent. The
wavefunction describing the superconducting state will include not only the
pairing of charges, but also of the spins of the paired charges. Each pair is
usually in the form of a spin singlet, so there will also be a pairing energy
associated with transforming the spin singlet into the higher energy spin
triplet form without necessarily unbinding the charges. Here we use inelastic
neutron scattering to determine the wavevector-dependence of spin pairing in
La_{2-x}Sr_xCuO_4, the simplest high-temperature superconductor. We find that
the spin pairing energy (or 'spin gap') is wavevector independent, even though
superconductivity significantly alters the wavevector dependence of the spin
fluctuations at higher energies.


title: Plateaux Transitions in the Pairing Model:Topology and Selection Rule

abstract:
  Based on the two-dimensional lattice fermion model, we discuss transitions
between different pairing states. Each phase is labeled by an integer which is
a topological invariant and characterized by vortices of the Bloch
wavefunction. The transitions between phases with different integers obey a
selection rule. Basic properties of the edge states are revealed. They reflect
the topological character of the bulk. Transitions driven by randomness are
also discussed numerically.


title: The Quantum Hall Effect: Novel Excitations and Broken Symmetries

abstract:
  These pedagogical lecture notes present a general introduction to most
aspects of the integer and fractional quantum Hall effects. This is followed by
an extensive discussion of quantum Hall ferromagnetism, both for spins in
single-layer systems and `pseudospins' in double-layer systems. The effective
field theories describing various broken symmetry states and `skyrmion' and
`meron' spin textures are derived and discussed in some detail. Pedagogical
presentations on Berry phases and lowest Landau level projection are included
in appendices.


title: Kink motion in the Kramers problem for a chain molecule

abstract:
  We consider the generalization of the Kramers escape over a barrier problem
to the case of a long chain molecule. It involves the motion of chain molecule
of N segments across a region where the free energy per segment is higher, so
that it has to cross a barrier. We use the Rouse model and find that the free
energy of activation has a square root dependence on the temperature leading to
a non-Arrhenius form for the rate. We also show that there is a special time
dependent solution of the model, which corresponds to a kink in the chain,
confined to the region of the barrier. The polymer goes from one side to the
other by the motion of the kink in the reverse direction. If there is no free
energy difference between the two sides of the barrier, then the kink moves by
diffusion and the time of crossing t_{cross}~ N^2/T^{3/2}. If there is a free
energy difference, then the kink moves with a non-zero velocity from the lower
free energy side to the otherleading to t_{cross} ~ N/sqrt{T}.


title:
Zeeman response of d-wave superconductors: Born approximation for
  impurity and spin-orbit scattering potentials

abstract:
  The effects of impurity and spin-orbit scattering potentials can strongly
affect the Zeeman response of a d-wave superconductor. Here, both the phase
diagram and the quasiparticle density of states are calculated within the Born
approximation and it is found that the spin-orbit interaction influences in a
qualitatively different way the Zeeman response of d-wave and s-wave
superconductors.


title: Distinct charge and spin gaps in underdoped YBa2Cu3O7-x

abstract:
  A systamatic quantitative comparison of ''pseudogap'' values obtained from
the analysis of charge and spin excitation spectroscopies in underdoped
YBa2Cu3O7-x using a temperature-independent gap shows two distinct excitations,
one visible in spin-flip spectroscopies like NMR and spin polarized neutron
scattering, and the other in charge excitation spectoscopies like single
particle tunneling and time-resolved quasiparticle relaxation. Both appear to
decrease with doping x approximately as 1/x and are T-independent, existing
above and below Tc. We suggest that the charge excitation can be attributed to
a pair-breaking local gap, while the spin excitation can be explained by an
intra-gap local triplet state.


title: Pseudogap Induced by Superconducting Fluctuation in the d-p Model

abstract:
  Using the d-p model, we demonstrate that the pseudogap, which is induced by
the superconducting fluctuation, plays key roles in the determination of the
phase diagram observed in high-Tc superconducting materials. We take the
pairing interaction mediated by the spin fluctuation and calculate the
superconducting transition temperature Tc, the NMR relaxation rate 1/T1 and the
single-particle spectrum by treating both the superconducting fluctuation and
spin fluctuation in a consistent fashion. As temperature decreases, 1/T1T
increases at high temperatures, and it reaches a maximum followed by a sharp
drop in the underdoped region, due to the evolution of the pseudogap in the
single-particle spectrum. The evolution is also consistent with those of ARPES
experiments.


title:
Effect of the Equivalence Between Topological and Electric Charge on the
  Magnetization of the Hall Ferromagnet

abstract:
  The dependence on temperature of the spin magnetization of a two-dimensional
electron gas at filling factor unity is studied. Using classical Monte Carlo
simulations we analyze the effect that the equivalence between topological and
electrical charge has on the the behavior of the magnetization. We find that at
intermediate temperatures the spin polarization increases in a thirty per cent
due to the Hartree interaction between charge fluctuations.


title:
Specific-heat evidence for strong electron correlations in the
  thermoelectric material (Na,Ca)Co_{2}O_{4}

abstract:
  The specific heat of (Na,Ca)Co_{2}O_{4} is measured at low-temperatures to
determine the magnitude of the electronic specific-heat coefficient \gamma, in
an attempt to gain an insight into the origin of the unusually large
thermoelectric power of this compound. It is found that \gamma is as large as
48 mJ/molK^2, which is an order of magnitude larger than \gamma of simple
metals. This indicates that (Na,Ca)Co_{2}O_{4} is a strongly-correlated
electron system, where the strong correlation probably comes from the
low-dimensionality and the frustrated spin structure. We discuss how the large
thermopower and its dependence on Ca doping can be understood with the strong
electron correlations.


title: Static Properties of Trapped Bose-Fermi Mixed Condensate of Alkali Atoms

abstract:
  Static properties of a bose-fermi mixture of trapped potassium atoms are
studied in terms of coupled Gross-Pitaevskii and Thomas-Fermi equations for
both repulsive and attractive bose-fermi interatomic potentials. Qualitative
estimates are given for solutions of the coupled equations, and the parameter
regions are obtained analytically for the boson-density profile change and for
the boson/fermion phase separation. Especially, the parameter ratio $R_{int}$
is found that discriminates the region of the large boson-profile change. These
estimates are applied for numerical results for the potassium atoms and checked
their consistency. It is suggested that a small fraction of fermions could be
trapped without an external potential for the system with an attractive
boson-fermion interaction.


title:
Berry Phase and Ground State Symmetry in H x h Dynamical Jahn-Teller
  Systems

abstract:
  Due to the ubiquitous presence of a Berry phase, in most cases of dynamical
Jahn-Teller systems the symmetry of the vibronic ground state is the same as
that of the original degenerate electronic state. As a single exception, the
linear H x h icosahedral model, relevant to the physics of C60 cations, is
determined by an additional free parameter, which can be continuously tuned to
eliminate the Berry phase from the low-energy closed paths: accordingly, the
ground state changes to a totally-symmetric nondegenerate state.


title: Hopping with time-dependent disorder

abstract:
  We determine the propagation properties of a quantum particle in a
d-dimensional lattice with hopping disorder, delta-correlated in time. The
system is delocalized: the averaged transition probability shows a diffusive
behavior. Then, superimposed to the disorder, we consider a bias favouring the
motion with a given orientation, as in the dynamics of flux lines in
superconductors. The result is an effective Liouvillian for the density matrix,
which is characterized by competition between single particle and pair hopping.
In this case the transition probability is determined in terms of excitonic
motion, each exciton being extended along the bias direction and characterized
by a nontrivial dispersion law.


title: Cahn-Hilliard Theory for Unstable Granular Flows

abstract:
  A Cahn-Hilliard-type theory for hydrodynamic fluctuations is proposed that
gives a quantitative description of the slowly evolving spatial correlations
and structures in density and flow fields in the early stages of evolution of
freely cooling granular fluids. Two mechanisms for pattern selection and
structure formation are identified: unstable modes leading to density
clustering (compare spinodal decomposition), and selective noise reduction
(compare peneplanation in structural geology) leading to vortex structures. As
time increases, the structure factor for the density field develops a maximum,
which shifts to smaller wave numbers. This corresponds to an approximately
diffusively growing length scale for density clusters. The spatial velocity
correlations exhibit algebraic decay $\sim r^{-d}$ on intermediate length
scales. The theoretical predictions for spatial correlation functions and
structure factors agree well with molecular dynamics simulations of a system of
inelastic hard disks.


title: A Bayesian Approach to Inverse Quantum Statistics

abstract:
  A nonparametric Bayesian approach is developed to determine quantum
potentials from empirical data for quantum systems at finite temperature. The
approach combines the likelihood model of quantum mechanics with a priori
information over potentials implemented in form of stochastic processes. Its
specific advantages are the possibilities to deal with heterogeneous data and
to express a priori information explicitly, i.e., directly in terms of the
potential of interest. A numerical solution in maximum a posteriori
approximation was feasible for one--dimensional problems. Using correct a
priori information turned out to be essential.

categories: cond-mat.stat-mech cond-mat.dis-nn physics.data-an quant-ph


title:
Non-Hermitian tridiagonal random matrices and returns to the origin of a
  random walk

abstract:
  We study a class of tridiagonal matrix models, the "q-roots of unity" models,
which includes the sign ($q=2$) and the clock ($q=\infty$) models by Feinberg
and Zee. We find that the eigenvalue densities are bounded by and have the
symmetries of the regular polygon with $2 q$ sides, in the complex plane.
Furthermore the averaged traces of $M^k$ are integers that count closed random
walks on the line, such that each site is visited a number of times multiple of
$q$. We obtain an explicit evaluation for them.


title: Incomplete descriptions and relevant entropies

abstract:
  Statistical mechanics relies on the complete though probabilistic description
of a system in terms of all the microscopic variables. Its object is to derive
therefrom static and dynamic properties involving some reduced set of
variables. The elimination of the irrelevant variables is guided by the maximum
entropy criterion, which produces the probability law carrying the least amount
of information compatible with the relevant variables. This defines relevant
entropies which measure the missing information (the disorder) associated with
the sole variables retained in an incomplete description. Relevant entropies
depend not only on the state of the system but also on the coarseness of its
reduced description. Their use sheds light on questions such as the Second Law,
both in equilibrium an in irreversible thermodynamics, the projection method of
statistical mechanics, Boltzmann's \textit{H}-theorem or spin-echo experiment.


title: Novel structural features of the ripple phase of phospholipids

abstract:
  We have calculated the electron density maps of the ripple phase of
dimyristoylphosphatidylcholine (DMPC) and palmitoyl-oleoyl phosphatidylcholine
(POPC) multibilayers at different temperatures and fixed relative humidity. Our
analysis establishes, for the first time, the existence of an average tilt of
the hydrocarbon chains of the lipid molecules along the direction of the ripple
wave vector, which we believe is responsible for the occurrence of asymmetric
ripples in these systems.


title:
Neutron diffraction evidence of microscopic charge inhomogeneities in
  the CuO2 plane of superconducting La2-xSrxCuO4 (0 < x <0.30)

abstract:
  We present local structural evidence supporting the presence of charge
inhomogeneities in the CuO2 planes of underdoped La2-xSrxCuO4. High-resolution
atomic pair distribution functions have been obtained from neutron powder
diffraction data over the range of doping 0 < x < 0.30 at 10 K. Despite the
average structure getting less orthorhombic we see a broadening of the in-plane
Cu-O bond distribution as a function of doping up to optimal doping. Thereafter
the peak abruptly sharpens. Complementary evidence is also evident from the
observation of octahedral tilt disorder in the PDF at higher atomic separation.
This suggests a crossover from a charge inhomogeneous state at and below
optimal doping to a homogeneous charge state above optimal doping. The strong
response of the local structure to the charge-state implies a strong
electron-lattice coupling in these materials.


title:
Enhanced fluctuations of the tunneling density of states near bottoms of
  Landau bands measured by a local spectrometer

abstract:
  We have found that the local density of states fluctuations (LDOSF) in a
disordered metal, detected using an impurity in the barrier as a spectrometer,
undergo enhanced (with respect to SdH and dHvA effects) oscillations in strong
magnetic fields, omega _c\tau > 1. We attribute this to the dominant role of
the states near bottoms of Landau bands which give the major contribution to
the LDOSF and are most strongly affected by disorder. We also demonstrate that
in intermediate fields the LDOSF increase with B in accordance with the results
obtained in the diffusion approximation.


title:
Confinement and Bose Condensation in Gauge Theory of High-Tc
  Superconductors

abstract:
  The issue of confinement and bose condensation is studied for gauge models of
high-Tc superconductors. First the Abelian-Higgs model in (2+1)D, i.e.,
XY-model coupled to lattice gauge field $a_{\mu}$ with coupling $g$, is studied
taking into account both the instantons and vortices. This model corresponds to
integer filling of the bosons, and can be mapped to a dual superconductor. Our
main resut is that the instantons introduce a term which couples linearly to
the dual superconductor order parameter, and tend to pin its phase. As a result
the vortex condensation always occurs due to the instantons, and the Meissner
effect for the gauge field $a_\mu$ is absent, although $a_{\mu}$ is massive.
This state is essentially the same as the confining phase of the pure gauge
model. Away from integer filling, a ``magnetic field'' $\mu$ (the chemical
potential of the bosons) is applied to this dual superconductor. Then the Higgs
phase revives in the case of weak $g$ and large $x$, where vortices do not
condense in spite of the instantons. In the opposite case, i.e., strong $g$ and
small $x$, phase separation occurs, forming either microscopic patches or
macroscopic stripe domains of the Mott insulating state.


title: Transmission Through Carbon Nanotubes With Polyhedral Caps

abstract:
  We study electron transport between capped carbon nanotubes and a substrate,
and relate the transmission probability to the local density of states in the
cap. Our results show that the transmission probability mimics the behavior of
the density of states at all energies except those that correspond to localized
states in the cap. Close proximity of a substrate causes hybridization of the
localized state. As a result, new transmission paths open from the substrate to
nanotube continuum states via the localized states in the cap. Interference
between various transmission paths gives rise to antiresonances in the
transmission probability, with the minimum transmission equal to zero at
energies of the localized states. Defects in the nanotube that are placed close
to the cap cause resonances in the transmission probability, instead of
antiresonances, near the localized energy levels. Depending on the spatial
position of defects, these resonant states are capable of carrying a large
current. These results are relevant to carbon nanotube based studies of
molecular electronics and probe tip applications.


title: c-axis Josephson Tunneling in Twinned YBCO Crystals

abstract:
  Josephson tunneling between YBCO and Pb with the current flowing along the
c-axis of the YBCO is persumed to come from an s-wave component of the
superconductivity of the YBCO. Experiments on multi-twin samples are not
entirely consistent with this hypothesis. The sign change of the s-wave order
parameter across the N_T twin boundaries should give cancelations, resulting in
a small $(\sqrt{N})$ tunneling current. The actual current is larger than this.
We present a theory of this unexpectedly large current based upon a surface
effect: disorder-induced supression of the d-wave component at the (001)
surface leads to s-wave coherence across the twin boundaries and a non-random
tunneling current. We solve the case of an ordered array of d+s and d-s twins,
and estimate that the twin size at which s-wave surface coherence occurs is
consistent with typical sizes observed in experiments. In this picture, there
is a phase difference of $\pi/2$ between different surfaces of the material. We
propose a corner junction experiment to test this picture.


title:
Dynamical Breaking of Charge Neutrality in Intrinsic Josephson
  Junctions: Common Origin for Microwave Resonant Absorptions and
  Multiple-branch Structures in the I-V Characterisitcs

abstract:
  We demonstrate that both microwave resonant absorptions and multiple-branch
structures in the I-V characterisitcs observed in intrinsic Josephson junctions
(IJJ's) are caused by dynamical breaking of charge neutrality (DBCN) inside the
atomic-scale superconducting layer. The Lagranginan for the time-dependent
Lawrence-Doniach model incorporating the effect of the DBCN is proposed, and
the longitudinal collective Josephson plasma mode is proved to exist based on
the Lagrangian. On the other hands, the branching behaviors in the I-V curves
are almost completely reproduced by careful numerical simulations for the model
equation derived from the Lagragian.


title: The steady state quantum statistics of a non-Markovian atom laser

abstract:
  We present a fully quantum mechanical treatment of a single-mode atomic
cavity with a pumping mechanism and an output coupling to a continuum of
external modes. This system is a schematic description of an atom laser. In the
dilute limit where atom-atom interactions are negligible, we have been able to
solve this model without making the Born and Markov approximations. When
coupling into free space, it is shown that for reasonable parameters there is a
bound state which does not disperse, which means that there is no steady state.
This bound state does not exist when gravity is included, and in that case the
system reaches a steady state. We develop equations of motion for the two-time
correlation in the presence of pumping and gravity in the output modes. We then
calculate the steady-state output energy flux from the laser.


title:
The Sixth-Moment Sum Rule For the Pair Correlations of the
  Two-Dimensional One-Component Plasma: Exact Result

abstract:
  The system under consideration is a two-dimensional one-component plasma in
fluid regime, at density n and at arbitrary coupling Gamma=beta e^2 (e=unit
charge, beta = inverse temperature). The Helmholtz free energy of the model, as
the generating functional for the direct pair correlation c, is treated in
terms of a convergent renormalized Mayer diagrammatic expansion in density.
Using specific topological transformations within the bond-renormalized Mayer
expansion we prove that the nonzero contributions to the regular part of the
Fourier component of c up to the k^2-term originate exclusively from the ring
diagrams (unable to undertake the bond-renormalization procedure) of the
Helmholtz free energy. In particular, c(k)=-Gamma/k^2 + Gamma/(8 pi n) -
k^2/[96(pi n)^2] + O(k^4). This result fixes via the Ornstein-Zernike relation,
besides the well-known zeroth-, second- and fourth- moment sum rules, the new
six-momnt condition for the truncated pair correlation h, n(pi Gamma n/2)^3
Integral r^6 h(r) d^2 r = 3(Gamma-6)(8-3 Gamma)/4.


title:
Generalized Random Phase Approximation: Zero and Non-Zero Temperature
  Properties of an Interacting Electron Gas

abstract:
  Correlated systems at both zero and nonzero temperature are treated here from
a novel angle using a functional method. This functional method is an extension
of the usual effective potential method. Here, however the effective action is
made to depend explicitly on the correlation effects that are inherent in the
physics involved. This will enable us to obtain new expressions for the free
energy, the specific heat and the ground state energy. The new expansion is
shown to give the expected results for the homogeneous case at zero
temperature. However at non-zero temperature we are able to get new sets of
diagrams that have a vanishing effect at zero temperature. To lowest order
these diagrams if summed properly will solve a ln T anomaly in the specific
heat of an electron gas at low temperature. We are also able to show that this
method provides a very clear way to extend the RPA approximation. We calculate
the effect of exchange on the ring diagrams at zero temperature and show how to
include some of the ladder digrams. Our results agree well with known numerical
calculations. We conclude by showing that this method is in fact a variant of
the time dependent density functional method and can in principle be applied to
study the effects of correlation in the nonhomogeneous case.


title: Contact resistance of quantum tubes

abstract:
  We consider the conductance of a quantum tube connected to a metallic
contact. The number of angular momentum states that the tube can support
depends on the strength of the radial confinement. We calculate the
transmission coefficients which yield the conductance via the Landauer formula.
We relate our results to armchair carbon nanotubes embedded in a metal. For Al
and Au contacts and tubes with a realistic radial confinement we find that the
transmission can be close to unity corresponding to a contact resistance close
to h/2e^2 per band at the Fermi level in the carbon nanotube.


title:
Shot-noise in non-degenerate semiconductors with energy-dependent
  elastic scattering

abstract:
  We investigate current fluctuations in non-degenerate semiconductors, on
length scales intermediate between the elastic and inelastic mean free paths.
The shot-noise power P is suppressed below the Poisson value P_{\rm
Poisson}=2e\bar I (at mean current \bar I) by the Coulomb repulsion of the
carriers. We consider a power-law dependence of the elastic scattering time
\tau\propto\epsilon^{\alpha} on kinetic energy \epsilon and present an exact
solution of the non-linear kinetic equations in the regime of space-charge
limited conduction. The ratio P/P_{\rm Poisson} decreases from 0.38 to 0 in the
range -1/2 < \alpha < 1.


title:
Low-energy electronic structure in Y1-xCaxBa2Cu3O7-y comparison of t
  ime-resolved optical spectroscopy, NMR, neutron and tunneling data

abstract:
  Time-resolved optical measurements give information on the quasiparticle
relaxation dynamics in YBCO, from which the evolution of the gap with doping
and temperature can be systematically deduced. In this paper these optical
charge-channel `pseudogap' data are compared with the `pseudogap' obtained from
the NMR Knight shift Ks, spin polarized neutron scattering (SPNS) and single
particle tunneling measurements. A simple energy level diagram is proposed to
explain the different `gap' magnitudes observed by different spectroscopies in
Y1-xCaxBa2Cu3O7-y, whereby the spin gap Delta_s in NMR and SPNS corresponds to
a triplet local pair state, while Delta_p in the charge excitation spectrum
corresponds to the pair dissociation energy. At optimum doping and in the
overdoped state, an additional T-dependent gap becomes evident, which closes at
T_c, suggesting a cross-over to a more conventional BCS-like superconductivity
scenario.


title: Dimensional crossover in dipolar magnetic layers

abstract:
  We investigate the static critical behaviour of a uniaxial magnetic layer,
with finite thickness L in one direction, yet infinitely extended in the
remaining d dimensions. The magnetic dipole-dipole interaction is taken into
account. We apply a variant of Wilson's momentum shell renormalisation group
approach to describe the crossover between the critical behaviour of the 3-D
Ising, 2-d Ising, 3-D uniaxial dipolar, and the 2-d uniaxial dipolar
universality classes. The corresponding renormalisation group fixed points are
in addition to different effective dimensionalities characterised by distinct
analytic structures of the propagator, and are consequently associated with
varying upper critical dimensions. While the limiting cases can be discussed by
means of dimensional epsilon expansions with respect to the appropriate upper
critical dimensions, respectively, the crossover features must be addressed in
terms of the renormalisation group flow trajectories at fixed dimensionality d.


title:
Relationship between incommensurability and superconductivity in Peierls
  distorted charge-density-wave systems

abstract:
  We study the pairing potential induced by fluctuations around a
charge-density wave (CDW) with scattering vector Q by means of the Froehlich
transformation. For general commensurability M, defined as |k+M*Q>=|k>, we find
that the intraband pair scattering within the M subbands scales with M whereas
the interband pair scattering becomes suppressed with increasing CDW order
parameter. As a consequence superconductivity is suppressed when the Fermi
energy is located between the subbands as it is usually the case for nesting
induced CDW's, but due to the vertex renormalization it can be substantially
enhanced when the chemical potential is shifted sufficiently inside one of the
subbands. The model can help to understand the experimentally observed
dependence of the superconducting transition temperature from the stripe phase
incommensurability in the lanthanum cuprates.


title: A density functional study of lithium bulk and surfaces

abstract:
  We report the bulk and surface properties of lithium computed within a full
potential LCGTO formalism using both density functional theory and the
Hartree-Fock approximation. We examine the convergence of computed properties
with respect to numerical approximations and also explore the use of finite
temperature density functional theory. We demonstrate that fully converged
calculations reproduce cohesive properties, elastic constants, band structure,
and surface energies in full agreement with experimental data and, where
available, previous calculations.


title: Transport and magnetic properties of La_(1-x)Ca_xMnO_3-films (0.1<x<0.9)

abstract:
  By laser ablation we prepared thin films of the colossal magnetoresistive
compound La_(1-x)Ca_xMnO_3 with doping levels 0.1<x<0.9 on MgO substrates.
X-ray diffraction revealed epitaxial growth and a systematic decrease of the
lattice constants with doping. The variation of the transport and magnetic
properties in this doping series was investigated by SQUID magnetization and
electrical transport measurements. For the nonmetallic samples resistances up
to 10^13 Ohm have been measured with an electrometer setup. While the transport
data indicate polaronic transport for the metallic samples above the Curie
temperature the low doped ferromagnetic insulating samples show a variable
range hopping like transport at low temperature.


title:
Effect of thermal phase fluctuations on the superfluid density of
  two-dimensional superconducting films

abstract:
  High precision measurements of the complex sheet conductivity of
superconducting Mo77Ge23 thin films have been made from 0.4 K through Tc. A
sharp drop in the inverse sheet inductance, 1/L(T), is observed at a
temperature, Tc, which lies below the mean-field transition temperature, Tco.
Just below Tc, the suppression of 1/L(T) below its mean-field value indicates
that longitudinal phase fluctuations have nearly their full classical
amplitude, but they disappear rapidly as T decreases. We argue that there is a
quantum crossover at about 0.94 Tco, below which classical phase fluctuations
are suppressed.


title:
A-type Antiferromagnetic and C-type Orbital-Ordered State in LaMnO$_3$
  Using Cooperative Jahn-Teller Phonons

abstract:
  The effect of Jahn-Teller phonons on the magnetic and orbital structure of
LaMnO$_3$ is investigated using a combination of relaxation and Monte Carlo
techniques on three-dimensional clusters of MnO$_6$ octahedra. In the
physically relevant region of parameter space for LaMnO$_3$, and after
including small corrections due to tilting effects, the A-type
antiferromagnetic and C-type orbital structures were stabilized, in agreement
with experiments.


title: Quantum Phase Fluctuations in High Tc Superconductors

abstract:
  If phase coherence determines the superconducting transition temperature Tc
in the cuprate oxides, it is of great interest to understand the role that
dynamics of the phase fluctuation plays in bringing about depletion of the
superconducting condensate. We will show that a phase correlation function can
be calculated that allows us to describe depletion of superconducting
condensate as a result of the quantum fluctuation. In two dimension, dynamic
phase fluctuation or pair fluctuation gives rise to a condensate depletion
linear with temperature as T$\to O$ in superconductors with nodes at the fermi
surface.


title: A review of growing interfaces in quenched disordered media

abstract:
  We make a review of the two principal models that allows to explain the
imbibition of fluid in porous media. These models, that belong to the directed
percolation depinning (DPD) universality class, where introduced simultaneously
by the Tang and Leschhorn [Phys. Rev A 45, R8309 (1992)] and Buldyrev et al.
[Phys. Rev. A 45, R8313 (1992)] and reviewed by Braunstein et al. [J. Phys. A
32, 1801 (1999); Phys. Rev. E 59, 4243 (1999)]. Even these models have been
classified in the same universality class than the Kardar-Parisi-Zhang equation
[Phys. Rev. Lett. 56, 889, (1986)] with quenched noise (QKPZ), the
contributions to the growing mechanisms are quite different. The lateral
contribution in the DPD models, leads to an increasing of the roughness near
the criticality while in the QKPZ equation this contribution always flattens
the roughness. These results suggest that the QKPZ equation does not describe
properly the DPD models even when the exponents derived from this equation are
similar to the one obtained from the simulations of these models. This fact is
confirmed trough the deduced analytical equation for the Tang and Leschhorn
model. This equation has the same symmetries than the QKPZ one but its
coefficients depend on the balance between the driving force and the quenched
noise.


title:
Metal-insulator transition in a doubly orbitally degenerate model with
  correlated hopping

abstract:
  In the present paper we propose a doubly orbitally degenerate narrow-band
model with correlated hopping. The peculiarity of the model is taking into
account the matrix element of electron-electron interaction which describes
intersite hoppings of electrons. In particular, this leads to the concentration
dependence of the effective hopping integral. The cases of the strong and weak
Hund's coupling are considered. By means of a generalized mean-field
approximation the single-particle Green function and quasiparticle energy
spectrum are calculated. Metal-insulator transition is studied in the model at
different integer values of the electron concentration. With the help of the
obtained energy spectrum we find energy gap width and criteria of
metal-insulator transition.


title: The diameter of the world wide web

abstract:
  Despite its increasing role in communication, the world wide web remains the
least controlled medium: any individual or institution can create websites with
unrestricted number of documents and links. While great efforts are made to map
and characterize the Internet's infrastructure, little is known about the
topology of the web. Here we take a first step to fill this gap: we use local
connectivity measurements to construct a topological model of the world wide
web, allowing us to explore and characterize its large scale properties.

categories: cond-mat.dis-nn adap-org cond-mat.stat-mech cs.NI math-ph math.MP nlin.AO physics.comp-ph


title:
Experimental Study of the Inductance of Pinned Vortices in
  Superconducting YBa2Cu3O7-d Films

abstract:
  Using a two-coil mutual inductance method, we have measured the complex
resistivity, rho_v(T,Be), of pinned vortices in c-axis pulsed laser deposited
YBa2Cu3O7-d films with magnetic field Be applied perpendicular to the film. At
low frequencies, (<100 kHz), rho_v is inductive and is inversely proportional
to the Labusch parameter, the average vortex pinning force constant, kappa_exp.
The observed weakening of kappa_exp with Be is consistent with a simple model
based on linear pinning defects. Adding classical thermal fluctuations to the
model in a simple way describes the observed linear T dependence of rho_v,
below ~15 K and provides reasonable values for the effective radius (.3 nm to
>.8 nm) of the defects and the depth of the pinning potential. The success of
this model implies that thermal supercurrent (phase) fluctuations have their
full classical amplitude down to 5 K for frequencies below the characteristic
depinning frequency. To date, no sufficient theory exists to explain the data
between ~15 K and the vortex glass melting temperature.


title: Transport of Torsional Stress in DNA

abstract:
  It is well known that transcription can induce torsional stress in DNA,
affecting the activity of nearby genes or even inducing structural transitions
in the DNA duplex. It has long been assumed that the generation of significant
torsional stress requires the DNA to be anchored, forming a limited topological
domain, since otherwise it would spin almost freely about its axis. Previous
estimates of the rotational drag have, however, neglected the role of small
natural bends in the helix backbone. We show how these bends can increase the
drag several thousandfold relative to prior estimates, allowing significant
torsional stress even in linear, unanchored DNA. The model helps explain
several puzzling experimental results on structural transitions induced by
transcription of DNA.


title:
Topological universality of level dynamics in quasi-one-dimensional
  disordered conductors

abstract:
  Nonperturbative, in inverse Thouless conductance 1/g, corrections to
distributions of level velocities and level curvatures in quasi-one-dimensional
disordered conductors with a topology of a ring subject to a constant vector
potential are studied within the framework of the instanton approximation of
nonlinear sigma-model. It is demonstrated that a global character of the
perturbation reveals the universal features of the level dynamics. The
universality shows up in the form of weak topological oscillations of the
magnitude ~ exp(-g) covering the main bodies of the densities of level
velocities and level curvatures. The period of discovered universal
oscillations does not depend on microscopic parameters of conductor, and is
only determined by the global symmetries of the Hamiltonian before and after
the perturbation was applied. We predict the period of topological oscillations
to be 4/(pi)^2 for the distribution function of level curvatures in orthogonal
symmetry class, and 3^(1/2)/(pi) for the distribution of level velocities in
unitary and symplectic symmetry classes.


title:
Thermodynamic Limit in Chern-Simons System of Particles with MB
  Statistics

abstract:
  The reduced density matrices (RDMs) are calculated in the thermodynamic limit
for the Chern-Simons non-relativistic particle system and Maxwell-Boltzmann
(MB) statistics. It is established that they are zero outside of a diagonal and
well-behaved after a renormalization, depending on an arbitrary real number, if
the condition of neutrality holds.


title: Charge degree of freedom and single-spin fluid model in YBa_2Cu_4O_8

abstract:
  We present a 17O nuclear magnetic resonance study in the stoichiometric
superconductor YBa_2Cu_4O_8. A double irradiation method enables us to show
that, below around 180 K, the spin-lattice relaxation rate of plane oxygen is
not only driven by magnetic, but also significantly by quadrupolar
fluctuations, i.e. low-frequency charge fluctuations. In the superconducting
state, on lowering the temperature, the quadrupolar relaxation diminishes
faster than the magnetic one. These findings show that, with the opening of the
pseudo spin gap, a charge degree of freedom of mainly oxygen character is
present in the electronic low-energy excitation spectrum.


title: Weak localization effect on thermomagnetic phenomena

abstract:
  The quantum transport equation (QTE) is extended to study weak localization
(WL) effects on galvanomagnetic and thermomagnetic phenomena. QTE has many
advantages over the linear response method (LRM): (i) particle-hole asymmetry
which is necessary for the Hall effect is taken into account by the
nonequilibrium distribution function, while LRM requires expansion near the
Fermi surface, (ii) when calculating response to the temperature gradient, the
problem of WL correction to the heat current operator is avoided, (iii)
magnetic field is directly introduced to QTE, while the LRM deals with the
vector potential and and special attention should be paid to maintain gauge
invariance, e.g. when calculating the Nernst effect the heat current operator
should be modified to include the external magnetic field. We reproduce in a
very compact form known results for the conductivity, the Hall and the
thermoelectric effects and then we study our main problem, WL correction to the
Nernst coefficient (transverse thermopower).


title:
Small-amplitude normal modes of a vortex in a trapped Bose-Einstein
  condensate

abstract:
  We consider a cylindrically symmetric trap containing a small Bose-Einstein
condensate with a singly quantized vortex on the axis of symmetry. A
time-dependent variational Lagrangian analysis yields the small-amplitude
dynamics of the vortex and the condensate, directly determining the equations
of motion of the coupled normal modes. As found previously from the Bogoliubov
equations, there are two rigid dipole modes and one anomalous mode with a
negative frequency when seen in the laboratory frame.


title: Electron-electron relaxation in two-dimensional impure superconductors

abstract:
  The electron-electron relaxation in impure two-dimensional superconductors is
studied. All channels of the electron-electron interaction classified in the
Nambu representation are taken into account. It is shown that the recombination
relaxation rate originates from quasipartical processes associated with
fluctuations of the electron density and the phase of the order parameter. At
low temperatures the recombination relaxation rate has a double exponential
temperature dependence. The scattering relaxation rate at low temperatures has
a power law temperature dependence due to contributions from gapless collective
excitations, the phase modes. Two-layer superconductor-normal metal system is
also considered. It is shown that the recombination relaxation rate in the
superconducting layer has a single exponential factor at low temperatures in
comparison with a one layer superconducting system. This increase in the
recombination relaxation rate originates from the inter-layer Coulomb
interaction and may be used in constructing of superconducting radiation
detectors.


title: Zero-bias anomaly in one-dimensional tunneling contacts

abstract:
  We study the Coulomb interaction effects on the tunneling conductance of a
contact constructed of two parallel quantum wires. The following contacts are
considered: two clean identical quantum wires, two disordered identical quantum
wires, and asymmetric contact of one clean and another disordered quantum
wires. We show that the low-voltage anomaly of the tunneling conductance is
less singular than the low-energy anomaly of the one-particle density of
states.


title: Screening effects in the electron-optical phonon interaction

abstract:
  We show that recently reported unusual hardening of optical phonons
renormalized by the electron-phonon interaction is due to the neglect of
screening effects. When the electron-ion interaction is properly screened
optical phonons soften in three dimension. It is important that for
short-wavelength optical phonons screening is static while for long-wavelength
optical phonons screening is dynamic. In two-dimensional and one-dimensional
cases due to crossing of the nonperturbed optical mode with gapless plasmons
the spectrum of renormalized optical phonon-plasmon mode shows split momentum
dependence.


title:
The temperature dependent bandstructure of a ferromagnetic semiconductor
  film

abstract:
  The electronic quasiparticle spectrum of a ferromagnetic film is investigated
within the framework of the s-f model. Starting from the exact solvable case of
a single electron in an otherwise empty conduction band being exchange coupled
to a ferromagnetically saturated localized spin system we extend the theory to
finite temperatures. Our approach is a moment-conserving decoupling procedure
for suitable defined Green functions. The theory for finite temperatures
evolves continuously from the exact limiting case. The restriction to zero
conduction band occupation may be regarded as a proper model description for
ferromagnetic semiconductors like EuO and EuS. Evaluating the theory for a
simple cubic film cut parallel to the (100) crystal plane, we find some marked
correlation effects which depend on the spin of the test electron, on the
exchange coupling, and on the temperature of the local-moment system.


title:
Effects of nonmagnetic impurities on optical conductivity in strongly
  correlated systems

abstract:
  Effects of nonmagnetic impurities on optical conductivity in the systems of
antiferromagnetically correlated electrons are examined based on the Lanczos
exact diagonalization scheme. As a result of resonant scattering a
low-frequency peak in the optical conductivity is predicted to occur in the
presence of the nonmagnetic impurities, which is consistent with the observed
normal-state optical conductivity of ${\rm YBa_2}({\rm Cu}_{1-x}{\rm
Zn}_x)_3{\rm O}_{7-\delta}$. In addition, a relatively high and broad peak is
found to occur at a high frequency region as a consequence of the Heisenberg
interaction between electrons, in agreement with observation in the peak
position.


title:
Magnetoresistance in Heavily Underdoped YBa_2Cu_3O_{6+x}:
  Antiferromagnetic Correlations and Normal-State Transport

abstract:
  We report on a contrasting behavior of the in-plane and out-of-plane
magnetoresistance (MR) in heavily underdoped antiferromagnetic (AF)
YBa_2Cu_3O_{6+x} (x<0.37). The out-of-plane MR (I//c) is positive over most of
the temperature range and shows a sharp increase, by about two orders of
magnitude, upon cooling through the Neel temperature T_N. A contribution
associated with the AF correlations is found to dominate the out-of-plane MR
behavior for H//c from far above T_N, pointing to the key role of spin
fluctuations in the out-of-plane transport. In contrast, the transverse
in-plane MR (I//a(b);H//c) appears to be small and smooth through T_N, implying
that the development of the AF order has little effect on the in-plane
resistivity.


title: Replica and Glasses

abstract:
  In these two lectures I review our theoretical understanding of spin glasses
paying a particular attention to the basic physical ideas. We introduce the
replica method and we describe its probabilistic consequences (we stress the
recently discovered importance of stochastic stability). We show that the
replica method is not restricted to systems with quenched disorder. We present
the consequences on the dynamics of the system when it slows approaches
equilibrium are presented: they are confirmed by large scale simulations, while
we are still awaiting for a direct experimental


title: Surface Influence on Flux Penetration into HTS Bulks

abstract:
  The influence of surface treatment on AC loss in melt-processed quasi-single
crystal HTS was investigated with resonance oscillations technique. We have
found that amplitude dependencies of AC loss on magnetic field amplitude become
rather complicated after surface polishing. The experimental data show well
distinguished dynamic crossover from absence of barrier at low rates of field
variation to its appearence at higher rates. An explaination of such a dynamic
surface barrier appearance based on consideration of along surface vortex
propagation was suggested.


title:
Thermobaric Effect on Melt-Textured MBa$_2$Cu$_3$O$_{7-\delta}$ (M = Y,
  Nd)

abstract:
  The effect of a short (10-30 min) thermobaric action (in the 1-5 GPa pressure
and 700-1300$^\circ$C temperature range) on the structure, superconductive and
mechanical properties of melt-textured-MBa$_2$Cu$_3$O$_{7-\delta}$ (M=Y, Nd) or
MT-MBCO have been studied. The existence has been established of
pressure-temperature--time conditions (2 GPa, 800$^\circ$C for 30 min and
900-950$^\circ$C for 15 min for MT-YBCO; 5 GPa, 850-900$^\circ$C for 15 min for
MT-NdBCO) the treatment under which allows superconductive properties of the
materials (because of the contact with zirconia and high pressure) to be
preserved or improved, mechanical characteristics increased and the materials
condensed.


title: Quantum dot dephasing by edge states

abstract:
  We calculate the dephasing rate of an electron state in a pinched quantum
dot, due to Coulomb interactions between the electron in the dot and electrons
in a nearby voltage biased ballistic nanostructure. The dephasing is caused by
nonequilibrium time fluctuations of the electron density in the nanostructure,
which create random electric fields in the dot. As a result, the electron level
in the dot fluctuates in time, and the coherent part of the resonant
transmission through the dot is suppressed.