title:
Spectral Statistics and Dynamical Localization: sharp transition in a
  generalized Sinai billiard

abstract:
  We consider a Sinai billiard where the usual hard disk scatterer is replaced
by a repulsive potential with $V(r)\sim\lambda r^{-\alpha}$ close to the
origin. Using periodic orbit theory and numerical evidence we show that its
spectral statistics tends to Poisson statistics for large energies when
$\alpha<2$ and to Wigner-Dyson statistics when $\alpha>2$, while for $\alpha=2$
it is independent of energy, but depends on $\lambda$. We apply the approach of
Altshuler and Levitov [Phys. Rep. {\bf 288}, 487 (1997)] to show that the
transition in the spectral statistics is accompanied by a dynamical
localization-delocalization transition. This behaviour is reminiscent of a
metal-insulator transition in disordered electronic systems.


title: Dynamics of the Compact, Ferromagnetic \nu=1 Edge

abstract:
  We consider the edge dynamics of a compact, fully spin polarized state at
filling factor $\nu=1$. We show that there are two sets of collective
excitations localized near the edge: the much studied, gapless, edge
magnetoplasmon but also an additional edge spin wave that splits off below the
bulk spin wave continuum. We show that both of these excitations can soften at
finite wave-vectors as the potential confining the system is softened, thereby
leading to edge reconstruction by spin texture or charge density wave
formation. We note that a commonly employed model of the edge confining
potential is non-generic in that it systematically underestimates the texturing
instability.


title:
Computational Mechanics: Pattern and Prediction, Structure and
  Simplicity

abstract:
  Computational mechanics, an approach to structural complexity, defines a
process's causal states and gives a procedure for finding them. We show that
the causal-state representation--an $\epsilon$-machine--is the minimal one
consistent with accurate prediction. We establish several results on
$\epsilon$-machine optimality and uniqueness and on how $\epsilon$-machines
compare to alternative representations. Further results relate measures of
randomness and structural complexity obtained from $\epsilon$-machines to those
from ergodic and information theories.

categories: cond-mat.stat-mech adap-org chao-dyn nlin.AO nlin.CD


title:
Capillary Waves at Liquid/Vapor Interfaces: A Molecular Dynamics
  Simulation

abstract:
  Evidence for capillary waves at a liquid/vapor interface are presented from
extensive molecular dynamics simulations of a system containing up to 1.24
million Lennard-Jones particles. Careful measurements show that the total
interfacial width depends logarithmically on $L_\parallel$, the length of the
simulation cell parallel to the interface, as predicted theoretically. The
strength of the divergence of the interfacial width on $L_\parallel$ depends
inversely on the surface tension $\gamma$. This allows us to measure $\gamma$
two ways since $\gamma$ can also be obtained from the difference in the
pressure parallel and perpendicular to the interface. These two independent
measures of $\gamma$ agree provided that the interfacial order parameter
profile is fit to an error function and not a hyperbolic tangent, as often
assumed. We explore why these two common fitting functions give different
results for $\gamma$.


title:
On the nature of the transition from the spontaneously dimerized to the
  Neel phase in the two-dimensional J1-J2 model

abstract:
  We analyze the spectrum of the 2D S=1/2 frustrated Heisenberg model near the
transition from the spontaneously dimerized spin-liquid phase into the Neel
ordered phase. Two excitation branches: the triplet magnon, and the collective
singlet mode, both become gapless at the transition point. However we find that
the length scales associated with these modes are well separated at the quantum
transition. While in the quantum disordered phase the singlet excitation has
finite spectral weight and reflects the existence of spontaneous dimer order,
near the transition point the size of the singlet bound state grows
exponentially with the correlation length, and hence the quasiparticle residue
is exponentially small. Therefore the critical dynamics remains in the O(3)
universality class in spite of the four gapless modes.


title:
Na-site substitution effects of the thermoelectric properties of
  NaCo_2O_4

abstract:
  The resistivity and thermopower of Na$_{1+x}$Co$_2$O$_4$ and
Na$_{1.1-x}$Ca$_x$Co$_2$O$_4$ are measured and analyzed. In
Na$_{1+x}$Co$_2$O$_4$, whereas the resistivity increases with $x$, the
thermopower is nearly independent of $x$. This suggests that the excess Na is
unlikely to supply carriers, and decreases effective conduction paths in the
sample. In Na$_{1.1-x}$Ca$_x$Co$_2$O$_4$, the resistivity and the thermopower
increase with $x$, and the Ca$^{2+}$ substitution for Na$^+$ reduces the
majority carriers in NaCo$_2$O$_4$. This means that they are holes, which is
consistent with the positive sign of the thermopower. Strong correlation in
this compound is evidenced by the peculiar temperature dependence of the
resistivity.


title:
Nesting properties and anisotropy of the Fermi surface of
  LuNi$_{2}$B$_{2}$C

abstract:
  The rare earth nickel borocarbides, with the generic formula
$R$Ni$_{2}$B$_{2}$C, have recently been shown to display a rich variety of
phenomena. Most striking has been the competition between, and even coexistence
of, antiferromagnetism and superconductivity. We have measured the Fermi
surface (FS) of LuNi$_{2}$B$_{2}$C, and shown that it possesses nesting
features capable of explaining some of the phenomena experimentally observed.
In particular, it had previously been conjectured that a particular sheet of FS
is responsible for the modulated magnetic structures manifest in some of the
series. We report the first direct experimental observation of this sheet.


title: Theory of the pi state in 3He Josephson junctions

abstract:
  The flow of superfluid 3He-B through a 65 x 65 array of nanometer size
apertures has been measured recently by Backhaus et al. They find in the
current--phase relation a new branch, so-called pi state. We study two limiting
cases which show that the pi state arises from coupling of the phase degree of
freedom to the spin-orbit rotation. The pi state exists in a single large
aperture, but is difficult to observe because of hysteresis. A better
correspondence with experiments is obtained by assuming a thin wall, where the
Josephson coupling between the two sides arises from a dense array of
pin-holes.


title:
The Symmetries of the Order Parameters for Pairing and Phase Coherence
  in Hole-Doped Cuprates

abstract:
  The symmetries of the order parameter (OP) responsible for pairing and the OP
responsible for phase coherence in hole-doped cuprates are discussed. We
analyze angle-resolved tunneling, ARPES, Raman scattering and torque
measurements performed on hole-doped cuprates. We conclude that, most likely,
the OP responsible for phase coherence has the d-wave symmetry whereas the OP
responsible for pairing has an anisotropic s-wave symmetry.


title: Electronic Shell Structure of Nanoscale Superconductors

abstract:
  Motivated by recent experiments on Al nanoparticles, we have studied the
effects of fixed electron number and small size in nanoscale superconductors,
by applying the canonical BCS theory for the attractive Hubbard model in two
and three dimensions. A negative ``gap'' in particles with an odd number of
electrons as observed in the experiments is obtained in our canonical scheme.
For particles with an even number of electrons, the energy gap exhibits shell
structure as a function of electron density or system size in the weak-coupling
regime: the gap is particularly large for ``magic numbers'' of electrons for a
given system size or of atoms for a fixed electron density. The grand canonical
BCS method essentially misses this feature. Possible experimental methods for
observing such shell effects are discussed.


title:
Phase separation and enhanced charge-spin coupling near magnetic
  transitions

abstract:
  The generic changes of the electronic compressibility in systems which show
magnetic instabilities is studied. It is shown that, when going into the
ordered phase, the compressibility is reduced by an amount comparable to the
its original value, making charge instabilities also possible. We discuss,
within this framework, the tendency towards phase separation of the double
exchange systems, the pyrochlores, and other magnetic materials.


title: Scaling invariance in finance II: Path-dependent contingent claims

abstract:
  This article is the second one in a series on the use of scaling invariance
in finance. In the first article (cond-mat/9906048), we introduced a new
formalism for the pricing of derivative securities, which focusses on tradable
objects only, and which completely avoids the use of martingale techniques. In
this article we show the use of the formalism in the context of path-dependent
options. We derive compact and intuitive formulae for the prices of a whole
range of well known options such as arithmetic and geometric average options,
barriers, rebates and lookback options. Some of these have not appeared in the
literature before. For example, we find rather elegant formulae for double
barrier options with moving barriers, continuous dividends and all possible
configurations of the barriers. The strength of the formalism reveals itself in
the ease with which these prices can be derived. This allowed us to pinpoint
some mistakes regarding geometric mean options, which frequently appear in the
literature. Furthermore, symmetries such as put-call transformations appear in
a natural way within the framework.


title:
Collective charge-density excitations of non-circular quantum dots in a
  magnetic field

abstract:
  Recent photoabsorption measurements have revealed a rich fine structure in
the collective charge-density excitation spectrum of few-electron quantum dots
in the presence of magnetic fields. We have performed systematic computational
studies of the far-infrared density response of quantum dots, using
time-dependent density-functional theory in the linear regime and treating the
dots as two-dimensional disks. It turns out that the main characteristics
observed in the experiment can be understood in terms of the electronic shell
structure of the quantum dots. However, new features arise if a breaking of the
circular symmetry of the dots is allowed, leading to an improved description of
the experimental results.


title:
Magnetic field induced localization in a two-dimensional superconducting
  wire network

abstract:
  We report transport measurements on superconducting wire networks which
provide the first experimental evidence of a new localization phenomenon
induced by magnetic field on a 2D periodic structure. In the case of a
superconducting wave function this phenomenon manifests itself as a depression
of the network critical current and of the superconducting transition
temperature at a half magnetic flux quantum per tile. In addition, the strong
broadening of the resistive transition observed at this field is consistent
with enhanced phase fluctuations due to this localization mechanism.


title: Nonlinear Spin Dynamics in Ferromagnets with Electron-Nuclear Coupling

abstract:
  Nonlinear spin motion in ferromagnets is considered with nonlinearity due to
three factors: (i) the sample is prepared in a strongly nonequilibrium state,
so that evolution equations cannot be linearized as would be admissible for
spin motion not too far from equilibrium, (ii) the system considered consists
of interacting electron and nuclear spins coupled with each other via hyperfine
forces, and (iii) the sample is inserted into a coil of a resonant electric
circuit producing a resonator feedback field. Due to these nonlinearities,
coherent motion of spins can develop, resulting in their ultrafast relaxation.
A complete analysis of mechanisms triggering such a coherent motion is
presented. This type of ultrafast coherent relaxation can be used for studying
intrinsic properties of magnetic materials.


title:
Free Energy and Magnetic Penetration Depth of a $d$-Wave Superconductor
  in the Meissner State

abstract:
  We investigate the free energy and the penetration depth of a
quasi-two-dimensional d-wave superconductor in the presence of a weak magnetic
field by taking account of thermal, nonlocal and nonlinear effects. In an
approximation in which the superfluid velocity $v_s$ is assumed to be slowly
varying, the free energy is calculated and compared with available results in
several limiting cases. It is shown that either nonlocal or nonlinear effects
may cut off the linear-$T$ dependence of both the free energy and the
penetration depth in all the experimental geometries. At extremely low $T$, the
nonlocal effects will also generically modify the linear $H$ dependence of the
penetration depth ("nonlinear Meissner effect") in most experimental
geometries, but for supercurrents oriented along the nodal directions, the
effect may be recovered. We compare our predictions with existing experiments
on the cuprate superconductors.


title:
Reply to a Comment on "Is the nonlinear Meissner effect unobservable?
  (Phys. Rev. Lett. 81, 5640 (1998))" (Cond-mat/9812290)

abstract:
  We reply to a recent comment by Bhattacharya et. al. (cond-mat/9812290) on
our previous Letter (PRL 81, 5640 (1998)).


title:
Monte Carlo procedure for protein folding in lattice model.
  Conformational rigidity

abstract:
  A rigourous Monte Carlo method for protein folding simulation on lattice
model is introduced. We show that a parameter which can be seen as the rigidity
of the conformations has to be introduced in order to satisfy the detailed
balance condition. Its properties are discussed and its role during the folding
process is elucidated. This method is applied on small chains on
two-dimensional lattice. A Bortz-Kalos-Lebowitz type algorithm which allows to
study the kinetic of the chains at very low temperature is implemented in the
presented method. We show that the coefficients of the Arrhenius law are in
good agreement with the value of the main potential barrier of the system.


title:
Theory of NMR as a local probe for the electronic structure in the mixed
  state of the high-$T_c$ cuprates

abstract:
  We argue that nuclear magnetic resonance experiments are a site-sensitive
probe for the electronic spectrum in the mixed state of the high-$T_c$
cuprates. Within a spin-fermion model, we show that the Doppler-shifted
electronic spectrum arising from the circulating supercurrent changes the
low-frequency behavior of the imaginary part of the spin-susceptibility. For a
hexagonal vortex lattice, we predict that these changes lead to {\it (a)} a
unique dependence of the $^{63}$Cu spin lattice relaxation rate, $1/T_1$, on
resonance frequency, and {\it (b)} a temperature dependence of $T_1$ which
varies with frequency. We propose a nuclear quadrupole experiment to study the
effects of a uniform supercurrent on the electronic structure and predict that
$T_1$ varies with the direction of the supercurrent.


title:
Functional Bosonization of Non-Relativistic Fermions in $(2+1)$
  Dimensions

abstract:
  We analyze the universality of the bosonization rules in non-relativistic
fermionic systems in $(2+1)d$. We show that, in the case of linear fermionic
dispersion relations, a general fermionic theory can be mapped into a gauge
theory in such a way that the fermionic density maps into a magnetic flux and
the fermionic current maps into a transverse electric field. These are
universal rules in the sense that they remain valid whatever the interaction
considered. We also show that these rules are universal in the case of
non-linear dispersion relations provided we consider only density-density
interactions. We apply the functional bosonization formalism to a
non-relativistic and non-local massive Thirring-like model and evaluate the
spectrum of collective excitations in several limits. In the large mass limit,
we are able to exactly calculate this spectrum for arbitrary density-density
and current-current interactions. We also analyze the massless case and show
that it has no collective excitations for any density-density potential in the
Gaussian approximation. Moreover, the presence of current interactions may
induce a gapless mode with a linear dispersion relation.


title: Interface resistance in ferromagnet/superconductor junctions

abstract:
  Results of theoretical study of spin-polarized tunneling in
ferromagnet/superconductor junctions are presented. Spin and charge currents
are calculated as a function of applied voltage and spin polarization in a
ferromagnet. The model takes into account the splitting of different spin
subbands in a ferromagnet and impurity scattering in the contact. The excess
resistance of an FS contact due to the charge-imbalance in a superconductor is
calculated for the first time. The results have implications for spin-coupled
magnetoresistance in ferromagnet/superconductor contacts and for measuring spin
polarization in ferromagnets.


title:
Ab initio study of the vapour-liquid critical point of a symmetrical
  binary fluid mixture

abstract:
  A microscopic approach to the investigation of the behaviour of a symmetrical
binary fluid mixture in the vicinity of the vapour-liquid critical point is
proposed. It is shown that the problem can be reduced to the calculation of the
partition function of a 3D Ising model in an external field. For a square-well
symmetrical binary mixture we calculate the parameters of the critical point as
functions of the microscopic parameter r measuring the relative strength of
interactions between the particles of dissimilar and similar species. The
calculations are performed at intermediate ($\lambda=1.5$) and moderately long
($\lambda=2.0$) intermolecular potential ranges. The obtained results agree
well with the ones of computer simulations.


title:
Effect of the pseudogap on the mean-field magnetic penetration depth of
  YBCO thin films

abstract:
  We report measurements of the magnetic penetration depth in YBCO films at
various oxygen concentrations. At optimal doping, critical fluctuation effects
are absent, and the penetration depth from 4 K to 0.99 Tc is well described by
d-wave, BCS, strong-coupling theory with a gap, Delta0/ kT ~ 3.3. This implies
that the T-dependence of the penetration depth comes largely from
single-particle excitations. As in crystals, underdoping reduces the zero
temperature superfluid density without affecting the low-T slope or curvature
of the penetration depth. We show that these results, as well as heat capacity
measurements, are well described by an ad hoc model in which superfluid is lost
from regions of the Fermi surface occupied by the pseudogap while the low lying
excitations near the nodes remain unaffected.


title:
Application of the discrete Wentzel-Kramers-Brillouin method to spin
  tunneling

abstract:
  A discrete version of the WKB method is developed and applied to calculate
the tunnel splittings between classically degenerate states of spin
Hamiltonians. The results for particular model problems are in complete accord
with those previously found using instanton methods. The discrete WKB method is
more elementary and also yields wavefunctions.


title: Coherent Magnetic Moment Reversal in Small Particles with Nuclear Spins

abstract:
  A discrete WKB method is developed for calculating tunnel splittings in spin
problems. The method is then applied to the issue of how nuclear spins affect
the macroscopic quantum coherence of the total magnetic moment in small
magnetic particles. The results are compared with numerical work, and with
previous instanton based analytic approaches.


title:
Kinetics of condensation of flexible polyelectrolytes in poor solvents:
  effects of solvent quality, valence and size of counterions

abstract:
  The collapse kinetics of strongly charged polyelectrolytes in poor solvents
is investigated by Langevin simulations and scaling arguments. The rate of
collapse increases sharply as the valence of counterions, z, increases from one
to four. The combined system of the collapsed chain and the condensed
counterions forms a Wigner crystal when the solvent quality is not too poor
provided z >= 2. For very poor solvents the morphology of the collapsed
structure resembles a Wigner glass. For a fixed z and quality of the solvent
the efficiency of collapse decreases dramatically as the size of the counterion
increases. A valence dependent diagram of states in poor solvents is derived.


title: Self-similar magnetoresistance of Fibonacci ultrathin magnetic films

abstract:
  We study numerically the magnetic properties (magnetization and
magnetoresistance) of ultra-thin magnetic films (Fe/Cr) grown following the
Fibonacci sequence. We use a phenomenological model which includes Zeeman,
cubic anisotropy, bilinear and biquadratic exchange energies. Our physical
parameters are based on experimental data recently reported, which contain
biquadratic exchange coupling with magnitude comparable to the bilinear
exchange coupling. When biquadratic exchange coupling is sufficiently large a
striking self-similar pattern emerges.


title: A simple deterministic self-organized critical system

abstract:
  We introduce a new continuous cellular automaton that presents self-organized
criticality. It is one-dimensional, totally deterministic, without any kind of
embedded randomness, not even in the initial conditions. This system is in the
same universality class as the Oslo rice pile system, boundary driven interface
depinning and the train model for earthquakes. Although the system is chaotic,
in the thermodynamic limit chaos occurs only in a microscopic level.


title: Group Theory Approach to Band Structure: Scarf and Lame Hamiltonians

abstract:
  The group theoretical treatment of bound and scattering state problems is
extended to include band structure. We show that one can realize Hamiltonians
with periodic potentials as dynamical symmetries, where representation theory
provides analytic solutions, or which can be treated with more general spectrum
generating algebraic methods. We find dynamical symmetries for which we derive
the transfer matrices and dispersion relations. Both compact and non-compact
groups are found to play a role.

categories: cond-mat math-ph math.MP nlin.SI solv-int


title: Two Definitions of Superfluid Density

abstract:
  We point out that two different definitions of the superfluid density -
through statistical response to static gauge phase and through dynamic response
to altering gauge phase - yield, generally speaking, different quantities in
$d<3$. The physics leading to this difference is associated with the
equilibrium statistics of supercurrent states. Some experimentally observable
consequences of this fact are discussed.


title: Plasmonic excitations in noble metals: The case of Ag

abstract:
  The delicate interplay between plasmonic excitations and interband
transitions in noble metals is described by means of {\it ab initio}
calculations and a simple model in which the conduction electron plasmon is
coupled to the continuum of electron-hole pairs. Band structure effects,
specially the energy at which the excitation of the $d$-like bands takes place,
determine the existence of a subthreshold plasmonic mode, which manifests
itself in Ag as a sharp resonance at 3.8 eV. However, such a resonance is not
observed in the other noble metals. Here, this different behavior is also
analyzed and an explanation is provided.


title:
An Approximate Sign Sum Rule for the Transmission Amplitude Through a
  Quantum Dot

abstract:
  We study the phase of the transmission amplitude through a disordered quantum
dot in the Coulomb blockade regime. We calculate the phase dependence on gate
voltage for a disorder configuration. We show that over a ``period'',
consisting of a resonance and a transmission valley, the total phase change is
0 (mod $2\pi$). Deviations from this sum rule are small in the parameter (level
spacing/charging energy). The disorder-averaged phase-phase correlation
function is found showing interaction-induced correlations between phases at
different gate voltages.


title: Electronic Structure and Heavy Fermion Behavior in LiV_2O_4

abstract:
  First principles density functional calculations of the electronic and
magnetic properties of spinel-structure LiV$_{2}$O$_{4}$ have been performed
using the full potential linearized augmented planewave method. The
calculations show that the electronic structure near the Fermi energy consists
of a manifold of 12 bands derived from V $t_{2g}$ states, weakly hybridized
with O p states. While the total width of this active manifold is approximately
2 eV, it may be roughly decomposed into two groups: high velocity bands and
flatter bands, although these mix in density functional calculations. The flat
bands, which are the more atomic-like lead to a high density of states and
magnetic instability of local moment character. The value of the on-site
exchange energy is sensitive to the exact exchange correlation parameterization
used in the calculations, but is much larger than the interaction between
neighboring spins, reflecting the weak coupling of the magnetic system with the
high velocity bands. A scenario for the observed heavy fermion behavior is
discussed in which conduction electrons in the dispersive bands are weakly
scattered by local moments associated with strongly correlated electrons in the
heavy bands.This is analogous to that in conventional Kondo type heavy
fermions, but is unusual in that both the local moments and conduction
electrons come from the same d-manifold.


title: Physics of rapidly expanding supercritical solutions: A first approach

abstract:
  We consider the case when a supercritical fluid emerges at sonic speed from a
small orifice in a high pressure chamber. The subsequent expansion causes a
pressure drop and the fluid then enters a regime where its equation of state in
$P-V$ space becomes concave towards the origin. This is the signal for an
expansion shock to occur in a non-ideal fluid. This paper provides the details
of an analytic calculation of the shape and location of this expansion shock
using Whitham's front-tracking method. Dependence of the shape of the front on
various operating conditions was calculated for the particular case of
supercritical carbon dioxide. The results shed light on the rapid expansion of
supercritical solutions (RESS), a process which is used in many manufacturing
technologies.

categories: cond-mat.soft cond-mat.mtrl-sci cond-mat.stat-mech physics.flu-dyn


title: Generic growth instabilities in one-layered tissue sheets

abstract:
  Growth and folding in one-layered model tissue sheets are studied in a
stochastic, lattice-free single cell model which considers the discrete
cellular structure of the tissue, and a coarse grained analytical approach. The
polarity of the tissue sheet is considered by a bending term. Cell division
gives rise to a locally increasing metric. An exponential and a power-law
growth regime are identified. In both regimes folding occurs as soon as the
bending contribution becomes too small to compensate the destabilizing effect
of the cell proliferation. The potential biological relevance is discussed.

categories: cond-mat.stat-mech cond-mat.soft physics.bio-ph q-bio


title: Electrolytic depletion interactions

abstract:
  We consider the interactions between two uncharged planar macroscopic
surfaces immersed in an electrolyte solution which are induced by interfacial
selectivity. These forces are taken into account by introducing a depletion
free-energy density functional, in addition to the usual mean-field
Poisson-Boltzmann functional. The minimization of the total free-energy
functional yields the density profiles of the microions and the electrostatic
potential. The disjoining pressure is obtained by differentiation of the total
free energy with respect to the separation of the surfaces, holding the range
and strength of the depletion forces constant. We find that the induced
interaction between the two surfaces is always repulsive for sufficiently large
separations, and becomes attractive at shorter separations. The nature of the
induced interactions changes from attractive to repulsive at a distance
corresponding to the range of the depletion forces.


title:
Mid-infrared Hall effect in thin-film metals: Probing the Fermi surface
  anisotropy in Au and Cu

abstract:
  A sensitive mid-infrared (MIR, 900-1100 cm-1, 112-136 meV) photo-elastic
polarization modulation technique is used to measure simultaneously Faraday
rotation and circular dichroism in thin metal films. These two quantities
determine the complex AC Hall conductivity. This novel technique is applied to
study Au and Cu thin films at temperatures down to 20 K and magnetic fields up
to 8 T. The Hall frequency is consistent with band theory predictions. We
report the first measurement of the MIR Hall scattering rate, which is
significantly lower than that derived from Drude analysis of zero magnetic
field MIR transmission measurements. This difference is qualitatively explained
in terms of the anisotropy of the Fermi surface in Au and Cu.


title: Phonons and hole localization in La(1.475)Nd(0.4)Sr(0.125)CuO(4)

abstract:
  The phonon densities-of-states of La(1.475)Nd(0.4)Sr(0.125)CuO(4) and
La(1.9)Sr(0.1)CuO(4) were measured using inelastic neutron scattering. The ~70
meV phonon band which appears due to hole doping in La(1.9)Sr(0.1)CuO(4) is
known to arise from strong electron-lattice coupling. This phonon band is
strongly suppressed in the Nd-doped compound for which T_c is also suppressed,
establishing a link between in-plane oxygen optical phonons and
superconductivity. This suppression is attributed to hole localization which
becomes strong near the stripe ordering condition of certain cuprates near
x=1/8 and competes with superconductivity.


title:
Zero-Conductance Resonances due to Flux States in Nanographite Ribbon
  Junctions

abstract:
  The electronic transport properties through junctions in nanographite ribbons
are investigated using the Landauer approach. In the low-energy regime ribbons
with zigzag boundary have a single conducting channel of edge states. The
conductance as a function of the chemical potential shows a rich structure with
sharp dips of zero conductance. Each zero-conductance resonance is connected
with a resonant state which can be interpreted as the superposition of two
degenerate flux states with Kekul\'e-like current patterns. These
zero-conductance dips are connected with a pronounced negative magneto
resistance.


title: Superheated and Dissipative Ginzburg-Landau Superconductors

abstract:
  We study two superconducting systems using the Landau-Ginzburg equations. The
first is a superconducting half-space with an applied magnetic field parallel
to the surface. We calculate the maximum applied field that still supports
superconductivity in the material by solving the Landau-Ginzburg equations
analytically in asymptotic regimes of the Landau-Ginzburg parameter, kappa.
These results are then checked against numerical studies.
  The other system is a thin, current-carrying strip. Here we do the first
systematic study of nucleation of superconductivity in a normal strip and of
the motion of a normal-superconducting interface in the presence of a current.
This dissipative system requires solving the time-dependent Landau-Ginzburg
equations analytically and numerically.


title:
Critical Exponents from Five-Loop Strong-Coupling phi^4-Theory in 4-
  epsilon Dimensions

abstract:
  With the help of strong-coupling theory, we calculate the critical exponents
of O(N)-symmetric phi^4-theories in 4- epsilon dimensions up to five loops with
an accuracy comparable to that achieved by Borel-type resummation methods.


title:
Dynamical Properties of the One-Dimensional Supersymmetric t-J Model: A
  View from Elementary Excitations

abstract:
  Dynamical properties, such as dynamical spin and charge structure factors and
single-particle spectral functions, are studied for the one-dimensional
supersymmetric t-J model with inverse-square interaction. Exact diagonalization
and the recursion method are used for finite systems up to 16 sites. A simple
rule is proposed to understand the supermultiplet structure in the excitation
spectrum. Numerical calculations show that the dynamical spin structure factor
is independent of the electron density in the region where only two spinons
contribute. In the electron removal spectrum from half-filling, close
correspondence is found between the dominant contribution from three-spinon
plus one-holon states in the t-J model and the two-spinon excitations in the
Haldane-Shastry model. Comparison is made with dynamics of the nearest-neighbor
supersymmetric t-J model.


title: Influence of shape of quantum dots on their far-infrared absorption

abstract:
  We investigate the effects of the shape of quantum dots on their far-infrared
absorption in an external magnetic field by a model calculation. We focus our
attention on dots with a parabolic confinement potential deviating from the
common circular symmetry, and dots having circular doughnut shape. For a
confinement where the generalized Kohn theorem does not hold we are able to
interprete the results in terms of a mixture of a center-of-mass mode and
collective modes reflecting an excitation of relative motion of the electrons.
The calculations are performed within the time-dependent Hartree approximation
and the results are compared to available experimental results.


title:
Have your cake and eat it too: increasing returns while lowering large
  risks!

abstract:
  Based on a faithful representation of the heavy tail multivariate
distribution of asset returns introduced previously (Sornette et al., 1998,
1999) that we extend to the case of asymmetric return distributions, we
generalize the return-risk efficient frontier concept to incorporate the
dimensions of large risks embedded in the tail of the asset distributions. We
demonstrate that it is often possible to increase the portfolio return while
decreasing the large risks as quantified by the fourth and higher order
cumulants. Exact theoretical formulas are validated by empirical tests.


title:
First evidence for charge ordering in NaV$_2$O$_5$ from Raman
  spectroscopy

abstract:
  We argue on the basis of symmetry selection rules and Raman scattering
spectra that NaV$_2$O$_5$ undergoes a charge ordering phase transition at
T$_c$=34 K. Such a transition is characterized by the redistribution of the
charges at the phase transition and corresponds to the change of the vanadium
ions, from uniform V$^{4.5+}$ to two different V$^{4+}$ and V$^{5+}$ states. In
the low temperature phase the V$^{4+}$ ions are forming a "zig-zag" ladder
structure along the {\bf b}-axis, consistent with the symmetry of the P2/b
space group.


title:
Statistics of closed paths in two-dimensional systems and negative
  magnetoresistance studied by computer simulation

abstract:
  Statistics of closed paths in two-dimensional systems, which just determines
the interference quantum correction to conductivity and anomalous
magnetoconductance, has been studied by computer simulation of a particle
motion over the plane with randomly distributed scatters. Both ballistic and
diffusion regimes have been considered. The results of simulation have been
analyzed in the framework of diffusion approximation. They are used for
calculation of the magnetic field dependence of magnetoconductance in the model
2D system. It is shown that the anomalous magnetoconductance can be in
principle described by the well known expression, obtained in the diffusion
approximation, but with the prefactor less than unity and phase breaking which
differs from true value.


title: Magneto-thermodynamics of the spin-1/2 Kagome antiferromagnet

abstract:
  In this paper, we use a new hybrid method to compute the thermodynamic
behavior of the spin-1/2 Kagome antiferromagnet under the influence of a large
external magnetic field. We find a T^2 low-temperature behavior and a very low
sensitivity of the specific heat to a strong external magnetic field. We
display clear evidence that this low temperature magneto-thermal effect is
associated to the existence of low-lying fluctuating singlets, but also that
the whole picture (T^2 behavior of Cv and thermally activated spin
susceptibility) implies contribution of both non magnetic and magnetic
excitations. Comparison with experiments is made.


title: The Wigner molecule in a 2D quantum dot

abstract:
  The charge density and pair correlation function of three interacting
electrons confined within a two-dimensional disc-like hard wall quantum dot are
calculated by full numerical diagonalization of the Hamiltonian. The formation
of a Wigner-molecule in the form of equilateral triangular configuration for
electrons is observed as the size of the dot is increased.


title: Evaporative cooling of trapped fermionic atoms

abstract:
  We propose an efficient mechanism for the evaporative cooling of trapped
fermions directly into quantum degeneracy. Our idea is based on an electric
field induced elastic interaction between trapped atoms in spin symmetric
states. We discuss some novel general features of fermionic evaporative cooling
and present numerical studies demonstrating the feasibility for the cooling of
alkali metal fermionic species $^6$Li, $^{40}$K, and $^{82,84,86}$Rb. We also
discuss the sympathetic cooling of fermionic hyperfine spin mixtures, including
the effects of anisotropic interactions.


title: On Pseudogaps in One-Dimensional Models with Quasi-Long-Ranged-Order

abstract:
  We use analytic and numerical methods to determine the density of states of a
one-dimensional electron gas coupled to a spatially random quasi-static
back-scattering potential of long correlation length. Our results provide
insight into the 'pseudogap' phenomenon occurring in underdoped high-Tc
superconductors, quasi-one-dimensional organic conductors and liquid metals.
They demonstrate the important role played by amplitude fluctuations of the
backscattering potential and by fluctuations in gradients of the potential, and
confirm the importance of the self-consistency which is a key feature of the
'FLEX'-type approximations for the electron Green's function. Our results allow
an assessment of the merits of different approximations: a previous approximate
treatment presented by Sadovskii and, we show, justified by a WKB approximation
gives a reasonably good representation, except for a ``central peak'' anomaly,
of our numerically computed densities of states, whereas a previous
approximation introduced by Lee, Rice and Anderson is not as accurate.


abstract:
  Vortex structures in dilute quantum fluids are studied using the
Gross-Pitaevskii equation. The velocity and momentum of multiply quantized
vortex rings are determined and their core structures analysed. For flow past a
spherical object, we study the encircling and pinned ring solutions, and
determine their excitation energies as a function of the flow velocity for both
penetrable and impenetrable objects. The ring and laminar flow solutions
converge at a critical velocity, which decreases with increasing object size.
We also study the vortex solutions associated with flow past a surface bump
which indicate that surface roughness also reduces the critical velocity. This
effect may have important implications for the threshold of dissipation in
superfluids and superconductors.


title:
Electrostatic Repulsion of Positively Charged Vesicles and Negatively
  Charged Objects

abstract:
  A positively charged, mixed bilayer vesicle in the presence of negatively
charged surfaces (for example, colloidal particles) can spontaneously partition
into an adhesion zone of definite area, and another zone that repels additional
negative objects. Although the membrane itself has nonnegative charge in the
repulsive zone, negative counterions on the interior of the vesicle
spontaneously aggregate there, and present a net negative charge to the
exterior. Beyond the fundamental result that oppositely charged objects can
repel, our mechanism helps explain recent experiments on surfactant vesicles.


title:
High $T_c$ Phase Diagram based on the SU(2) Slave-Boson Approach to the
  t-J Hamiltonian

abstract:
  Based on an improved SU(2) slave-boson approach to the t-J Hamiltonian, we
derive a phase diagram of high $T_c$ cuprates which displays both the
superconducting and pseudogap phases in the plane of temperature vs. hole
doping rate. It is shown that the inclusion of phase fluctuations in the order
parameters results in a closer agreement with the observed superconducting
temperature(bose condensation line) of an arch shape as a function of hole
doping rate.


title: Cavity atom optics and the `free atom laser'

abstract:
  The trap environment in which Bose-Einstein condensates are generated and/or
stored strongly influences the way they interact with light. The situation is
analogous to cavity QED in quantum optics, except that in the present case, one
tailors the matter-wave mode density rather than the density of modes of the
optical field. Just as in QED, for short times, the atoms do not sense the trap
and propagate as in free space. After times long enough that recoiling atoms
can probe the trap environment, however, the way condensates and light fields
are mutually influenced differs significantly from the free-space situation. We
use as an example the condensate collective atomic recoil laser, which is the
atomic matter-wave analog of the free-electron laser.


title: Stripe phases in high-temperature superconductors

abstract:
  Stripe phases are predicted and observed to occur in a class of
strongly-correlated materials describable as doped antiferromagnets, of which
the copper-oxide superconductors are the most prominent representative. The
existence of stripe correlations necessitates the development of new principles
for describing charge transport, and especially superconductivity, in these
materials.


title: Nonlinear Measures for Characterizing Rough Surface Morphologies

abstract:
  We develop a new approach to characterizing the morphology of rough surfaces
based on the analysis of the scaling properties of contour loops, i.e. loops of
constant height. Given a height profile of the surface we perform independent
measurements of the fractal dimension of contour loops, and the exponent that
characterizes their size distribution. Scaling formulas are derived and used to
relate these two geometrical exponents to the roughness exponent of a
self-affine surface, thus providing independent measurements of this important
quantity. Furthermore, we define the scale dependent curvature and demonstrate
that by measuring its third moment departures of the height fluctuations from
Gaussian behavior can be ascertained. These nonlinear measures are used to
characterize the morphology of computer generated Gaussian rough surfaces,
surfaces obtained in numerical simulations of a simple growth model, and
surfaces observed by scanning-tunneling-microscopes. For experimentally
realized surfaces the self-affine scaling is cut off by a correlation length,
and we generalize our theory of contour loops to take this into account.


title:
Quasiclassical theory of superconductivity: a multiple interface
  geometry(II)

abstract:
  A new method which allows one to study multiple coherent
reflection/transmissions by partially transparent interfaces, (e.g., in
multi-layer mesoscopic structures or grain boundaries in high-Tc's), in the
framework of the quasiclassical theory of superconductivity is suggested. It is
argued that in the presence of interfaces, a straight-line trajectory
transforms to a simple connected 1-dimensional tree (graph) with knots, i.e.
the points where the interface scattering events occur and pieces of the
trajectories are coupled. For the 2-component trajectory "wave function" which
factorizes the matrix Gor'kov Green's function, a linear boundary condition on
the knot is formulated for an arbitrary interface, specular or diffusive (in
the many channel model). From the new boundary condition, we derive: (i) the
excitation scattering amplitude for the multi-channel Andreev/ordinary
reflection/transmission processes; (ii) the boundary conditions for the Riccati
equation; (iii) the transfer matrix which couples the trajectory Green's
function before and after the interface scattering. To show the usage of the
method, the cases of a film separated from a bulk superconductor by a partially
transparent interface, and a SIS' sandwich with finite thickness layers, are
considered. The electric current response to the vector potential (the
superfluid density $\rho_s$) with the $\pi $ phase difference in S and S' is
calculated for the sandwich. It is shown that the model is very sensitive to
imperfection of the SS' interface: the low temperature response being
paramagnetic ($\rho_s <0$) in the ideal system case, changes its sign and
becomes diamagnetic ($\rho_s > 0$) when the probability of reflection is as low
as a few percent.


title: Higher anisotropic d-wave symmetry in cuprate superconductors

abstract:
  We derive a pair potential from tight binding further neighbours attraction
that leads to superconducting gap symmetry similar to that of the
phenomenological spin fluctuation theory of high temperature superconductors
(Monthoux, Balatsky, Pines, Phys. Rev. Lett. {\bf 67}, 3448). We show that
higher anisotropic d-wave than the simpliest d-wave symmetry is one of the
important ingredients responsible for higher BCS characteristic ratio.


title: Radiation from an electron bunch flying over a surface wave

abstract:
  Radiation generated by the passage of a monoenergetic electron bunch above
the surface wave excited in plane interface between homogeneous media with
different dielectric constants is investigated. For the surface wave of general
profile the radiation intensity is expressed via the radiated power from a
single charge and bunch form factor. Various types of transverse and
longitudinal distributions of electrons in the bunch have been considered
including Gaussian, asymmetrical Gaussian, two Gaussian and rectangular
distribution with asymmetrical exponential tails. Conditions are specified
under which the coherent radiation essentially exceeds the incoherent part.


title:
Ground-State Properties of a Rotating Bose-Einstein Condensate with
  Attractive Interaction

abstract:
  The ground state of a rotating Bose-Einstein condensate with attractive
interaction in a quasi-one-dimensional torus is studied in terms of the ratio
$\gamma$ of the mean-field interaction energy per particle to the
single-particle energy-level spacing. The plateaus of quantized circulation are
found to appear if and only if $\gamma<1$ with the lengths of the plateaus
reduced due to hybridization of the condensate over different angular-momentum
states.


title:
Self - affinity of ordinary Levy motion, spurious multi - affinity and
  pseudo - Gaussian relations

abstract:
  The ordinary Levy motion is a random process whose stationary independent
increments are statistically self-affine and distributed with a stable
probability law characterized by the Levy index alpha, 0 < alpha < 2. The
divergence of statistical moments of the order q > alpha leads to an important
role of the finite sample effects. The objective of this paper is to study the
influence of these effects on the self-affine properties of the ordinary Levy
motion, namely, on the '1/alpha laws', that is, time dependence of the q-th
order structure function and of the range. Analytical estimates and simulations
of the finite sample effects clearly demonstrates three phenomena: spurious
multi-affinity of the Levy motion, strong dependence of the structure function
on the sample size at q > alpha, and pseudo-Gaussian behavior of the
second-order structure function and of the normalized range. We discuss these
phenomena in detail and propose the modified Hurst method for empirical
rescaled range analysis.


title:
`One-sided' log-normal distribution of conductances of a disordered
  quantum wire

abstract:
  We develop a simple systematic method, valid for all strengths of disorder,
to obtain analytically for the first time the full distribution of conductance
P(g) for a quasi one dimensional wire in the absence of electron-electron
interaction. We show that in the crossover region between the metallic and
insulating regimes, P(g) is highly asymmetric, given by an essentially `one
sided' log-normal distribution. For larger disorder, the tail of the log-normal
distribution for g > 1 is cut off by a Gaussian.


title: Andreev scattering in nanoscopic junctions at high magnetic fields

abstract:
  We report on the measurement of multiple Andreev resonances at atomic size
point contacts between two superconducting nanostructures of Pb under magnetic
fields higher than the bulk critical field, where superconductivity is
restricted to a mesoscopic region near the contact. The small number of
conduction channels in this type of contacts permits a quantitative comparison
with theory through the whole field range. We discuss in detail the physical
properties of our structure, in which the normal bulk electrodes induce a
proximity effect into the mesoscopic superconducting part.


title:
Resonant Raman scattering in NaV2O5 as a probe of its electronic
  structure

abstract:
  In order to investigate the origin of the phase transition observed in
NaV$_2$O$_5$, as well as its electronic structure, we have measured Raman
intensities as a function of the laser wavelength above and below the phase
transition temperature. In the polarized Raman spectra at room temperature we
observe resonant enhancement of the 969 $cm^{-1}$ phonon mode when the laser
energy approaches 2.7 eV, presumably related to the (p-d) electron hopping
band, $O_3$($p_y$)-V($d_{xy}$), at 3.2 eV. The 969 $cm^{-1}$ mode originates
from the stretching vibrations along the c-axis involving the V-$O_1$ bonds.
Since an ellipsometric determination of the dielectric function $\epsilon_{cc}$
yields no structure in the 1.7 to 5.5 eV photon energy range, we conclude that
plane bonds couple strongly with the apical oxygens leading to a large Raman
efficiency. In the low-temperature Raman spectra, almost all modes that become
active below the phase transition temperature T$_c$=34 K show resonant
behavior. The most interesting ones, those at 66 and 106 $cm^{-1}$, possibly of
magnetic origin, exhibit a resonant intensity enhancement, approximately by an
order of magnitude, for laser photon energies around 1.85 eV with respect to
2.43 eV. This resonance effect may be associated with a weak absorption band
around 2 eV. Finally, a destructive interference between the resonant and the
nonresonant contribution to the Raman scattering amplitude (i.e. an
antiresonance) is found in the spectra for most of the (bb) low-temperature
modes.


title: Scattering of plane-wave atomic vibrations in disordered structures

abstract:
  A theoretical analysis of the scattering of plane-wave atomic excitations in
disordered solids has been made in terms of the spectral densities.
Hybridization between transverse and longitudinal waves of approximately the
same frequency is demonstrated. The analytic results agree well with the
results obtained from computer simulation for a toy linear zig-zag chain model
and a model of vitreous silica constructed by molecular dynamics.


title: On the relation between the anyon and Calogero models

abstract:
  In order to achieve a dimensional reduction from dimension two to one not
only in phase space but also in configuration space, the lowest Landau level
(LLL) projection is not sufficient. One has also, in the LLL, to take the
vanishing magnetic field limit, a procedure which can be given a non ambiguous
meaning by means of a long distance regulator. As an illustration, the
equivalence of the LLL anyon model in the vanishing magnetic field limit to the
Calogero model is established. A thermodynamical argument is proposed which
supports this claim. Some general considerations in favor of an intimate
connexion between anyon and Haldane statistics are also given.


title:
Charge fluctuations in a quantum point contact attached to a
  superconducting lead

abstract:
  We show how to calculate the charge noise spectrum in a normal mesoscopic
conductor, which is capacitively coupled to a macroscopic gate, when this
conductor is attached to L normal leads and M superconducting leads, the only
restriction being that the superconducting leads must be at the same chemical
potential. We then proceed to examine results for a quantum point contact (QPC)
in a normal lead connecting to a superconductor. Of interest is the fluctuating
current in a gate capacitively coupled to a QPC. The results are compared with
the case when all leads are normal. We find a doubling of the equilibrium
charge fluctuations and a large enhancement (>2) in the current noise spectrum
to first order in |eV|, when a channel in the QPC is opening.


title:
The transition temperature of the dilute interacting Bose gas for $N$
  internal degrees of freedom

abstract:
  We calculate explicitly the variation $\delta T_c$ of the Bose-Einstein
condensation temperature $T_c$ induced by weak repulsive two-body interactions
to leading order in the interaction strength. As shown earlier by general
arguments, $\delta T_c/T_c$ is linear in the dimensionless product $an^{1/3}$
to leading order, where $n$ is the density and $a$ the scattering length. This
result is non-perturbative, and a direct perturbative calculation of the
amplitude is impossible due to infrared divergences familiar from the study of
the superfluid helium lambda transition. Therefore we introduce here another
standard expansion scheme, generalizing the initial model which depends on one
complex field to one depending on $N$ real fields, and calculating the
temperature shift at leading order for large $N$. The result is explicit and
finite. The reliability of the result depends on the relevance of the large $N$
expansion to the situation N=2, which can in principle be checked by systematic
higher order calculations. The large $N$ result agrees remarkably well with
recent numerical simulations.


title: Self-consistent theory of transport in superconducting wires

abstract:
  We study superconducting transport in homogeneous wires in the cases of both
equilibrium and nonequilibrium quasiparticle populations, using the
quasiclassical Green's function technique. We consider superconductors with
arbitrary current densities and impurity concentrations ranging from the clean
to the dirty limit. Local current conservation is guaranteed by ensuring that
the order parameter satisfies the self-consistency equation at each point. For
equilibrium transport, we compute the current, the order parameter amplitude,
and the quasiparticle density of states as a function of the superfluid
velocity, temperature, and disorder strength. Nonequilibrium is characterized
by incoming quasiparticles with different chemical potentials at each end of
the superconductor. We calculate the profiles of the electrostratic potential,
order parameter, and effective quasiparticle gap. We find that a transport
regime of current-induced gapless superconductivity can be achieved in clean
superconductors, the stability of this state being enhanced by nonequilibrium.


title: Comment on ``Stripes and the t-J Model''

abstract:
  This is a comment being submitted to Physical Review Letters on a recent
letter by Hellberg and Manousakis on stripes in the t-J model.


title:
Tunneling transverse to a magnetic field, and how it occurs in
  correlated 2D electron systems

abstract:
  We investigate tunneling decay in a magnetic field. Because of broken
time-reversal symmetry, the standard WKB technique does not apply. The decay
rate and the outcoming wave packet are found from the analysis of the set of
the particle Hamiltonian trajectories and its singularities in complex space.
The results are applied to tunneling from a strongly correlated 2D electron
system in a magnetic field parallel to the layer. We show in a simple model
that electron correlations exponentially strongly affect the tunneling rate.


title:
Low-energy quasiparticle states near extended scatterers in d-wave
  superconductors and their connection with SUSY quantum mechanics

abstract:
  Low-energy quasiparticle states, arising from scattering by single-particle
potentials in d-wave superconductors, are addressed. Via a natural extension of
the Andreev approximation, the idea that sign-variations in the superconducting
pair-potential lead to such states is extended beyond its original setting of
boundary scattering to the broader context of scattering by general
single-particle potentials, such as those due to impurities. The
index-theoretic origin of these states is exhibited via a simple connection
with Witten's supersymmetric quantum-mechanical model.


title: Conducting phase in the two-dimensional disordered Hubbard model

abstract:
  We study the temperature-dependent conductivity $\sigma(T)$ and spin
susceptibility $\chi(T)$ of the two-dimensional disordered Hubbard model.
Calculations of the current-current correlation function using the Determinant
Quantum Monte Carlo method show that repulsion between electrons can
significantly enhance the conductivity, and at low temperatures change the sign
of $d\sigma/dT$ from positive (insulating behavior) to negative (conducting
behavior). This result suggests the possibility of a metallic phase, and
consequently a metal-insulator transition,in a two-dimensional microscopic
model containing both interactions and disorder. The metallic phase is a
non-Fermi liquid with local moments as deduced from a Curie-like temperature
dependence of $\chi(T)$.


title:
Proximity effects and Andreev reflection in mesoscopic SNS junction with
  perfect NS interfaces

abstract:
  Low temperature transport measurements on superconducting film - normal metal
wire - superconducting film (SNS) junctions fabricated on the basis of 6 nm
thick superconducting polycrystalline PtSi films are reported. The structures
with the normal metal wires of two different lengths L=1.5 $\mu$m and L=6$\mu$m
and the same widths W=0.3$\mu$m are studied. Zero bias resistance dip related
to pair current proximity effect is observed for all junctions whereas the
subharmonic energy gap structure originating from phase coherent multiple
Andreev reflections have occurs only in the SNS junctions with short wires.


title:
Phase Changes in an Inelastic Hard Disk System with a Heat Bath under
  Weak Gravity for Granular Fluidization

abstract:
  We performed numerical simulations on a two-dimensional inelastic hard disk
system under gravity with a heat bath to study the dynamics of granular
fluidization. Upon increasing the temperature of the heat bath, we found that
three phases, namely, the condensed phase, locally fluidized phase, and
granular turbulent phase, can be distinguished using the maximum packing
fraction and the excitation ratio, or the ratio of the kinetic energy to the
potential energy.It is shown that the system behavior in each phase is very
different from that of an ordinary vibrating bed.


title: Phase transitions in the antiferroelectric-ferroelectric mixed systems

abstract:
  Phase diagram of solid solutions of antiferroelectric and ferroelectric
materials like PbZr$_{1-x}$Ti$_x$O$_3$ (PZT), Rb$_x$(NH$_4$)$_{1-x}$H$_2$PO$%
_4$ (RADP) is calculated at the region $x\leq 0.1$. Antiferroelectric and
ferroelectric order parameters (which correspond respectively to the difference
and sum of two sublattices ions shifts) were introduced for antiferroelectric
host lattice. Small admixture of ferroelectric component was considered as a
random electric field source. The influence of this field on both
aforementioned order parameters was calculated. Self consistent averaging with
calculated random field distribution function made it possible to obtain the
system of equations for order parameters of mixed system. The antiferroelectric
$T_a$ and ferroelectric $T_c$ phase transition temperature concentrational
dependence was expressed through the transition temperatures of the composition
and members. The obtained $T_a(x)$ dependence was shown to fit pretty good the
observed values for PZT and RADP. The application of the proposed theoretical
approach to other types of mixed systems is discussed.


title:
On the physical mechanisms of relaxation time distribution in disordered
  dielectrics

abstract:
  The distribution function of relaxation times in disordered dielectrics has
been calculated in the random field theory framework. For this purpose, we
first consider the dynamics of single two-orientable impurity electric dipole
in a random electric field $E$ created by the rest of impurities in disordered
ferroelectric. This dynamics is conveniently described by Langevin equation.
Relaxation time $\tau $ is then a reciprocal probability (calculated on the
base of Fokker-Planck equation) of the dipole transition through barrier in a
double-well potential (corresponding to two possible dipole orientations),
distorted by a random fields. The obtained dependence $\tau (E)$ made it
possible to obtain the expression for relaxation times distribution function
$F(\tau)$(via random fields distribution function $f(E)$. Latter function has
been calculated self-consistently in the random field theory framework.
Nonlinear random field contribution and effects of spatial correlations between
impurities have also been taken into account. It was shown that nonlinear
contribution of random field gives asymmetric shape of $F(\tau)$, while in
linear case it is symmetric. Comparison of calculated $F(\tau)$ curves with
those extracted from empirical Cole-Cole (CC), Davidson-Cole (DC),
Kohlrausch-William-Watts (KWW) and Havriliak-Negami (HN) functions had shown,
that they correspond to mixed ferro-glass phase with coexistence of short and
long-range order. Different forms of $F(\tau)$ are determined by linear (CC) or
nonlinear (DC, KWW, HN) contributions of random field.


title:
Progressive evolution of tunneling characteristics of in-situ fabricated
  intrinsic Josephson junctions in Bi_2Sr_2CaCu_2O_{8+delta} single crystals

abstract:
  Stacks of a few intrinsic tunnel junctions were micro-fabricated on the
surface of Bi-2212 single crystals. The number of junctions in a stack was
tailored by progressively increasing the height of the stack by ion-beam
etching, while its tunneling characteristics were measured in-situ in a vacuum
chamber for temperatures down to ~13 K. Using this in-situ etching/measurements
technique in a single piece of crystal, we systematically excluded any spurious
effects arising from variations in the junction parameters and made clear
analysis on the following properties of the surface and inner conducting
planes. First, the tunneling resistance and the current-voltage curves are
scaled by the surface junction resistance. Second, we confirm that the
reduction in both the gap and the superconducting transition temperature of the
surface conducting plane in contact with a normal metal is not caused by the
variation in the doping level, but is caused by the proximity contact. Finally,
the main feature of a junction is not affected by the presence of other
junctions in a stack in a low bias region.


title:
A simple solid-on-solid model of epitaxial film growth: submonolayer
  substrate coverage

abstract:
  In this work we investigate influence of substrate temperature on the surface
morphology for substrate coverage below one monolayer. The model of film growth
is based on random deposition enriched by limited surface diffusion. Also
anisotropy in the growth is involved. We found from computer simulations for
simple cubic lattice and solid-on-solid model, that the surface morphology
changes with increasing temperature from isotropically distributed isolated
small islands, through anisotropic 1-D stripes to larger 2-D anisotropic
islands and again randomly distributed single atoms. The transition is also
marked in height-height correlation function dependence on temperature, as
directly seen by snapshots from simulations. The results are in good
qualitative agreement with already published results of kinetic Monte Carlo
simulations, as well as with some experimental data.


title:
Origin of the Quasiparticle Peaks of Spectral Functions in High $T_c$
  Cuprates

abstract: This paper has been withdrawn by the author(s).


title:
Electron correlation effects and magnetic ordering at the Gd(0001)
  surface

abstract:
  Effects of electron correlation on the electronic structure and magnetic
properties of the Gd(0001) surface are investigated using of the full-potential
linearized augmented plane wave implementation of correlated band theory
("LDA+U"). The use of LDA+U instead of LDA (local density approximation) total
energy calculations produces the correct ferromagnetic ground state for both
bulk Gd and the Gd surface. Surface strain relaxation leads to an 90 %
enhancement of the interlayer surface-to-bulk effective exchange coupling.
Application of a Landau-Ginzburg type theory yields a 30 % enhancement of the
Curie temperature at the surface, in very good agreement with the experiment.


title: Orbital Ordering and Resonant X-ray Scattering in Layered Manganites

abstract:
  In layered manganites with orbital and charge orderings, the degeneracy of
the Mn $4p$ orbitals as well as the $3d$ ones is lifted by the effects of the
$4p$ bands and the local Coulomb interactions. We formulate the atomic
scattering factor for the resonant x-ray scattering in the memory function
method by taking into account these effects on an equal footing. It is shown
that the polarization dependences of the scattering intensities at the orbital
and charge superlattice reflections observed in LaSr$_{2}$Mn$_2$O$_7$ are
caused by the local and itinerant characters of $4p$ electrons, respectively.
We examine the type of the orbital ordered state.


title:
Phase diagram of the half-filled Hubbard chain with
  next-nearest-neighbor hopping

abstract:
  We investigate the ground-state phase diagram of the half-filled
one-dimensional Hubbard model with next-nearest-neighbor hopping using the
Density-Matrix Renormalization Group technique as well as an unrestricted
Hartree-Fock approximation. We find commensurate and incommensurate disordered
magnetic insulating phases and a spin-gapped metallic phase in addition to the
one-dimensional Heisenberg phase. At large on-site Coulomb repulsion $U$, we
make contact with the phase diagram of the frustrated Heisenberg chain, which
has spin-gapped phases for sufficiently large frustration. For weak $U$,
sufficiently large next-nearest-neighbor hopping $t_2$ leads to a band
structure with four Fermi points rather than two, producing a spin-gapped
metallic phase. As $U$ is increased in this regime, the system undergoes a
Mott-Hubbard transition to a frustrated antiferromagnetic insulator.


title: Manifestation of intermediate spin for Fe$_{8}$

abstract:
  Intermediate spin, which occurs in the theory of anyons, can also be
exhibited by mesoscopic magnetic particles. The necessary broken time reversal
symmetry is due to a suitably directed magnetic field. As a function of this
field a system passes periodically through points which correspond to whole or
half-integer spin. Intermediate spin is defined by fields which lie between
these points. Since the tunnel splitting in the ground doublet vanishes for
half-integer spin, this splitting becomes periodic. The doubly periodic
oscillations observed in the magnetic molecular cluster Fe$_{8}$ represent the
first unequivocal observation of this phenomena. Here the whole or half-integer
nature of the system, i.e., the parity, is periodic for a field which is along
either the easy or hard axis or a suitable combination of the two. A detailed
theory is presented.


title: Doping Induced Magnetization Plateaus

abstract:
  The low temperature magnetization process of antiferromagnetic spin-S chains
doped with mobile spin-(S-1/2) carriers is studied in an exactly solvable
model. For sufficiently high magnetic fields the system is in a metallic phase
with a finite gap for magnetic excitations. In this phase which exists for a
large range of carrier concentrations x the zero temperature magnetization is
determined by x alone. This leads to plateaus in the magnetization curve at a
tunable fraction of the saturation magnetization. The critical behaviour at the
edges of these plateaus is studied in detail.


title: Correlation and response in the Backgammon model: the Ehrenfest legacy

abstract:
  We pursue our investigation of the non-equilibrium dynamics of the Backgammon
model, a dynamical urn model which exhibits aging and glassy behavior at low
temperature. We present an analytical study of the scaling behavior of the
local correlation and response functions of the density fluctuations of the
model, and of the associated fluctuation- dissipation ratios, throughout the
alpha regime of low temperatures and long times. This analysis includes the
aging regime, the convergence to equilibrium, sand the crossover behavior
between them.


title:
Spin gap behavior and charge ordering in \alpha^{\prime}-NaV_2O_5 probed
  by light scattering

abstract:
  We present a detailed analysis of light scattering experiments performed on
the quarter-filled spin ladder compound $\alpha^\prime$-NaV$_{2}$O$_{5}$ for
the temperature range 5 K$\le$T$\le$300 K. This system undergoes a phase
transition into a singlet ground state at T=34 K accompanied by the formation
of a super structure. For T$\leq$34 K several new modes were detected. Three of
these modes are identified as magnetic bound states. Experimental evidence for
charge ordering on the V sites is detected as an anomalous shift and splitting
of a V-O vibration at 422 cm$^{-1}$ for temperatures above 34 K. The smooth and
crossover-like onset of this ordering at T$_{\rm CO}$= 80 K is accompanied by
pretransitional fluctuations both in magnetic and phononic Raman scattering. It
resembles the effect of stripe order on the super structure intensities in
La$_2$NiO$_{4+\delta}$.


title: The size of electron-hole pairs in pi conjugated systems

abstract:
  We have performed momentum dependent electron energy-loss studies of the
electronic excitations in sexithiophene and compared the results to those from
parent oligomers. Our experiment probes the dynamic structure factor
S(q,omega)and we show that the momentum dependent intensity variation of the
excitations observed can be used to extract the size of the electron-hole pair
created in the excitation process. The extension of the electron-hole pairs
along the molecules is comparable to the length of the molecules and thus maybe
only limited by structural constraints. Consequently, the primary
intramolecular electron-hole pairs are relatively weakly bound. We find no
evidence for the formation of excitations localized on single thiophene units.


title: An alternative view on random tilings

abstract:
  We apply a framework for the description of random tilings without height
representation, which was proposed recently, to the special case of
quasicrystalline random tilings. Several important examples are discussed,
thereby demonstrating the consistency of this alternative description with the
conventional one. We also clarify the latter by deriving a group theoretic
criterion for the validity of the first random tiling hypothesis.


title:
Thermal and Tunneling Pair Creation of Quasiparticles in Quantum Hall
  Systems

abstract:
  We make a semiclassical analysis of thermal pair creations of quasiparticles
at various filling factors in quantum Hall systems. It is argued that the gap
energy is reduced considerably by the Coulomb potential made by impurities. It
is also shown that a tunneling process becomes important at low temperature and
at strong magnetic field. We fit typical experimental data excellently based on
our semiclassical results of the gap energy.


title: Correlation Effects on Optical Conductivity of FeSi

abstract:
  Effects of electron correlation in FeSi are studied in terms of the two-band
Hubbard model with the density of states obtained from the band calculation.
Using the self-consistent second-order perturbation theory combined with the
local approximation, the correlation effects are investigated on the density of
states and the optical conductivity spectrum, which are found to reproduce the
experiments done by Damascelli et al. semiquantitatively. It is also found that
the peak at the gap edge shifts to lower energy region by correlation effects,
as is seen in the experiments.


title:
Charge and spin inhomogeneity as a key to the physics of the high Tc
  cuprates

abstract:
  We present a coherent scenario for the physics of cuprate superconductors,
which is based on a charge-driven inhomogeneity, i.e. the ``stripe phase''. We
show that spin and charge critical fluctuations near the stripe instability of
strongly correlated electron systems provide an effective interaction between
the quasiparticles, which is strongly momentum, frequency, temperature and
doping dependent. This accounts for the various phenomena occurring in the
overdoped, optimally and underdoped regimes both for the normal and the
superconductive phase.


title: Renormalization of the Spin-Peierls Transition due to Phonon Dynamics

abstract:
  We report results from a systematic strong-coupling expansion of a spin-1/2
Heisenberg chain coupled to Einstein phonons. In the non-adiabatic regime this
model is used to describe zero temperature properties of CuGeO3. The linked
cluster expansion allows the determination of observables in the thermodynamic
limit preserving the full lattice dynamics without a truncation of the phononic
Hilbert space. In particular, the spin gap and the dispersion of the elementary
triplet excitation are calculated up to 10th order in a dimer expansion. The
magnetic structure factor of the ground state is evaluated up to 6th order. We
show that the spin-phonon coupling leads to a renormalization of the elementary
triplet dispersion. Surprisingly in the non-adiabatic regime a substantial
renormalization of the spin gap only sets in at much larger couplings than
those proposed for CuGeO3. The ground state magnetic correlations are found to
be hardly effected by the spin-phonon coupling, but dominated by the
frustrating magnetic interaction in the parameter regime relevant for CuGeO3.


title:
Spin-triplet superconductivity in Sr$_2$RuO$_4$ probed by Andreev
  reflection

abstract:
  The superconducting gap function of Sr$_2$RuO$_4$ was investigated by means
of quasiparticle reflection and transmission at the normal
conductor-superconductor interface of Sr$_2$RuO$_4$-Pt point contacts. We found
two distinguishly different types of $dV/dI$ vs $V$ spectra either with a
double-minimum structure or with a zero-bias conductance anomaly. Both types of
spectra are expected in the limit of high and low transparency, respectively,
of the interface barrier between a normal metal and a spin-triplet
superconductor. Together with the temperature dependence of the spectra this
result strongly supports a spin-triplet superconducting order parameter for
Sr$_2$RuO$_4$.


title: Edge Theories for Polarized Quantum Hall States

abstract:
  Starting from recently proposed bosonic mean field theories for fully and
partially polarized quantum Hall states, we construct corresponding effective
low energy theories for the edge modes. The requirements of gauge symmetry and
invariance under global O(3) spin rotations, broken only by a Zeeman coupling,
imply boundary conditions that allow for edge spin waves. In the generic case,
these modes are chiral, and the spin stiffness differs from that in the bulk.
For the case of a fully polarized $\nu=1$ state, our results agree with
previous Hartree-Fock calculations.


title: Scaling of folding properties in simple models of proteins

abstract:
  Scaling of folding properties of proteins is studied in a toy system -- the
lattice Go model with various two- and three- dimensional geometries of the
maximally compact native states. Characteristic folding times grow as power
laws with the system size. The corresponding exponents are not universal.
Scaling of the thermodynamic stability also indicates size-related
deterioration of the folding properties.


title:
Log-periodic power law bubbles in Latin-American and Asian markets and
  correlated anti-bubbles in Western stock markets: An empirical study

abstract:
  Twenty-two significant bubbles followed by large crashes or by severe
corrections in the Argentinian, Brazilian, Chilean, Mexican, Peruvian,
Venezuelan, Hong-Kong, Indonesian, Korean, Malaysian, Philippine and Thai stock
markets indices are identified and analysed for log-periodic signatures
decorating an average power law acceleration. We find that log-periodic power
laws adequately describe speculative bubbles on these emerging markets with
very few exceptions and thus extend considerably the applicability of the
proposed rational expectation model of bubbles and crashes which has previously
been developed for the major financial markets in the world. This model is
essentially controlled by a crash hazard rate becoming critical due to a
collective imitative/herding behavior of traders. Furthermore, three of the
bubbles are followed by a log-periodic ``anti-bubble'' previously documented
for the decay of the Japanese Nikkei starting in Jan. 1990 and the price of
Gold starting in Sept. 1980 thus rendering a qualitative symmetry of bubble and
anti-bubble around the date of the peak of the market. A set of secondary
western stock market indices (London, Sydney, Auckland, Paris, Madrid, Milan,
Zurich) as well as the Hong-Kong stock market are also shown to exhibit
well-correlated log-periodic power law anti-bubbles over a period 6-15 months
triggered by a rash of crises on emerging markets in the early 1994. As the US
market declined by no more than 10% during the beginning of that period and
quickly recovered, this suggests that these smaller stock western markets can
``phase lock'' (in a weak sense) not only because of the over-arching influence
of Wall Street but also independently of the current trends on Wall Street due
to other influences.


title:
Decrease of Ac Losses in High Tc Superconducting Tapes by Application of
  a DC Current

abstract:
  The ac losses in a silver-gold alloy sheathed Bi-2223 tape were measured by
the null calorimetric method while a dc current was superimposed onto the ac
current. As expected through computer simulations, a Clem valley was observed
for the larger ac currents. A reduction of ac losses of approximately 50% at
the valley minimum is observed in accord with the calculations. At lower ac
currents, the data fit the calculated behavior with a single parameter, a
Meissner current of 21.8 A. It is shown that a surface barrier current is
incompatible with the data.


title: Comment on ``Temperature Dependence of the Josephson Current''

abstract:
  Assertions by Overhauser of error in accepted calculations of the temperature
dependence of the Josephson current are shown to be without merit.


title: Functional Methods and Effective Potentials for Nonlinear Composites

abstract:
  A formulation of variational principles in terms of functional integrals is
proposed for any type of local plastic potentials. The minimization problem is
reduced to the computation of a path integral. This integral can be used as a
starting point for different approximations. As a first application, it is
shown how to compute to second-order the weak-disorder perturbative expansion
of the effective potentials in random composite. The three-dimensional results
of Suquet and Ponte-Casta\~neda (1993) for the plastic dissipation potential
with uniform applied tractions are retrieved and extended to any space
dimension, taking correlations into account. In addition, the viscoplastic
potential is also computed for uniform strain rates.


title: Orbital Dependent Exchange-Only Methods for Periodic Systems

abstract:
  Various orbital-dependent exchange-only potentials are studied which exhibit
correct long-range asymptotic behaviour. We present the first application of
these potentials for polymers and by one of these potentials for molecules.
Kohn-Sham type calculations have been carried out for polyethylene in order to
make valuable comparison of these potentials with each other as well as with
Hartree-Fock and exchange-only LDA methods. The Kohn-Sham band gap obtained
with the optimized effective potetial method is corrected with the exchange
contribution to the derivative discontinuity of the exchange-correlation
potential. The corrected band gap obtained with the Slater's exchange potential
is 9.7 eV close to the experiment.


title:
Critical behaviour of the 2d spin diluted Ising model via the
  equilibrium ensemble approach

abstract:
  The equilibrium ensemble approach to disordered systems is used to
investigate the critical behaviour of the two dimensional Ising model in
presence of quenched random site dilution. The numerical transfer matrix
technique in semi- infinite strips of finite width, together with
phenomenological renormalization and conformal invariance, is particularly
suited to put the equilibrium ensemble approach to work. A new method to
extract with great precision the critical temperature of the model is proposed
and applied. A more systematic finite-size scaling analysis than in previous
numerical studies has been performed. A parallel investigation, along the lines
of the two main scenarios currently under discussion, namely the logarithmic
correction scenario (with critical exponents fixed in the Ising universality
class) versus the weak universality scenario (critical exponents varying with
the degree of disorder), is carried out. In interpreting our data, maximum care
is costantly taken to be open in both directions. A critical discussion shows
that, still, an unambiguous discrimination between the two scenarios is not
possible on the basis of the available finite-size data.


title: Spin waves in a two dimensional p-wave superconductor: Sr$_2$RuO$_4$

abstract:
  We study spin excitations in a two dimensional p-wave superconductor with
${\vec \Delta} = {\hat d}({\hat k}_1 \pm i {\hat k}_2)$ symmetry in the context
of the newly discovered superconducting Sr$_2$RuO$_4$. The polarization and
spectrum of spin wave excitations are identified and their experimental
consequences are discussed.


title:
Quasiparticle Interface States in Junctions Involving d-Wave
  Superconductors

abstract:
  Influence of surface pair breaking, barrier transmission and phase difference
on quasiparticle bound states in junctions with d-wave superconductors is
examined. Based on the quasiclassical theory of superconductivity, an approach
is developed to handle interface bound states. It is shown in SIS' junctions
that low energy bound states get their energies reduced by surface pair
breaking, which can be taken into account by introducing an effective order
parameter for each superconductor at the junction barrier. More interestingly,
for the interface bound states near the continuous spectrum the effect of
surface pair breaking may result in a splitting of the bound states. In the
tunneling limit this can lead to a square root dependence of a nonequilibrium
Josephson current on the barrier transmision, which means an enhancement as
compared to the conventional critical current linear in the transmission.
Reduced broadening of bound states in NIS junctions due to surface pair
breaking is found.


title: Quantum Theory of Quantum-Hall Smectics

abstract:
  We propose a quantum stripe (smectic) coupled-Luttinger-liquid model for the
anisotropic states which occur in two-dimensional electron systems with
high-index partial Landau level filling, $\nu^{*} = \nu - \lbrack\nu\rbrack$.
Perturbative renormalization group calculations establish that interaction
terms neglected in this model are relevant - probably driving the system into
an anisotropic Wigner crystal---but for $0.4 \lesssim \nu^{*} \lesssim 0.6$
only below temperatures which are outside of the experimentally accessible
range. We argue that the Hall conductance of the ground state flows toward
$\lbrack\nu\rbrack e^{2}/h$ and $(\lbrack\nu\rbrack + 1) e^{2}/h$ respectively,
on the low and high filling factor sides of this range, consistent with recent
observations. A semiclassical theory of smectic state transport properties,
which incorporates Luttinger liquid effects in the evaluation of scattering
amplitudes, accounts for the magnitude of the dissipative resistivities at
$\nu^{*}=1/2$, for their $\nu^{*}$-dependence, and for the observation of
non-linearities of opposite sign in easy and hard direction resistivities.


title:
Ultraslow Electron Spin Dynamics in GaAs Quantum Wells Probed by
  Optically Pumped NMR

abstract:
  Optically pumped nuclear magnetic resonance (OPNMR) measurements were
performed in two different electron-doped multiple quantum well samples near
the fractional quantum Hall effect ground state nu=1/3. Below 0.5K, the spectra
provide evidence that spin-reversed charged excitations of the nu=1/3 ground
state are localized over the NMR time scale of ~40 microseconds. Furthermore,
by varying NMR pulse parameters, the electron spin temperature (as measured by
the Knight shift) could be driven above the lattice temperature, which shows
that the value of the electron spin-lattice relaxation time lies between 100
microseconds and 500 milliseconds at nu=1/3.


title:
Optically Pumped NMR Studies of Electron Spin Polarization and Dynamics:
  New Constraints on the Composite Fermion Description of nu = 1/2

abstract:
  The Knight shift and the nuclear spin-lattice relaxation rate 1/T1 of Ga-71
nuclei are measured in GaAs quantum wells at Landau level filling factor nu =
1/2 using optically pumped NMR. The temperature dependences of these data are
compared with predictions of a weakly-interacting composite fermion model. Our
measurements of the electron spin polarization and spin dynamics near the
transition between fully and partially spin-polarized ground states provide new
constraints on the theoretical description of nu = 1/2.


title: Interface and contact line motion in a two phase fluid under shear flow

abstract:
  A coarse grained description of a two phase fluid is used to study the steady
state configuration of the interface separating the coexisting phases, and the
motion of the contact line at which the interface intersects a solid boundary.
The fluid is set in motion by displacing two parallel, infinite solid
boundaries along their own plane. Dissipative relaxation of the order parameter
leads to interfacial slip at the contact line, even when no-slip boundary
conditions for the fluid velocity are considered. This relaxation occurs within
a characteristic length scale l that depends on the order parameter mobility,
the equilibrium interfacial tension, the imposed wall velocity, the thermal
correlation length, the equilibrium miscibility gap, and the mutual diffusion
coefficient. Steady-state interface equations which describe the system on a
length scale large compared to the correlation length are derived. Scaling
forms which involve the ratio l/L, where L is the width of the fluid layer, and
the capillary number follow from the interface equations. The scaling results
are verified by direct numerical solution of the governing equations.


title: Role of twin boundaries on the vortex dynamics in YBa$_2$Cu$_3$O$_7$

abstract:
  By means of a novel technique of rotating the applied current we have
directly measured the influence of twin boundaries on the vortex motion in a
YBa$_2$Cu$_3$O$_7$ single crystal. The results indicate that the effect of twin
planes on the vortex dynamics starts to develop below a certain temperature,
being responsible for an anisotropic viscosity in the vortex liquid state and a
guided motion in the solid state.


title:
Experimental investigation of universal parametric correlators using a
  vibrating plate

abstract:
  The parametric variation of the eigenfrequencies of a chaotic plate is
measured and compared to random matrix theory using recently calculated
universal correlation functions. The sensitivity of the flexural modes of the
plate to pressure is used to isolate this symmetry class of modes and simplify
the data analysis. The size of the plate is used as the external parameter and
the eigenvalues are observed to undergo one or two oscillations in the
experimental window. The correlations of the eigenvalues are in good agreement
with statistical measures such as the parametric number variance, the velocity
autocorrelation, and the intralevel velocity autocorrelation derived for the
Gaussian Orthogonal Ensemble of random matrix theory. Our results show that the
theory can be also applied to wave systems other than quantum systems.


title: Logarithmic Corrections in Quantum Impurity Problems

abstract:
  The effect of a BULK marginal operator on BOUNDARY critical phenomena in two
space-time dimensions is considered. The particular case of an open S=1/2
antiferromagnetic Heisenberg chain, corresponding to a Wess-Zumino-Witten
non-linear sigma model, is solved. In this case, the needed renormalization
group coefficient is associated with a novel operator product expansion in
which
  THREE operators approach the same point. Resulting logarithmic corrections
occurring in finite size calculations and nuclear magnetic resonance
experiments are discussed.


title: Transport in the Heavy Fermion Superconductor UPt3

abstract:
  We report new theoretical results and analysis for the transport properties
of superconducting UPt3 based on the leading models for the pairing symmetry.
We use Fermi surface data and the measured inelastic scattering rate to show
that the low-temperature thermal conductivity and transverse sound attenuation
in the A and B phase of UPt3 are in excellent agreement with pairing states
belonging to the two-dimensional orbital E2u representation.


title:
New Features of the Morphotropic Phase Boundary in the PbZr(1-x)TixO3
  System

abstract:
  Recently a new monoclinic phase in the PbZr(1-x)TixO3 ceramic system has been
reported by Noheda et al. for the composition x= 0.48. In the present work,
samples with Ti contents of x= 0.47 and 0.50, which are both tetragonal below
their Curie points, have been investigated. In the sample with x= 0.50, the
tetragonal phase was found to transform to a monoclinic phase at about 200 K as
the temperature was lowered. The sample with x= 0.47 showed a complicated
region of phase coexistence between 440-320 K, becoming rhombohedral at around
300 K. No further symmetry change was found down to 20 K. Dielectric
measurements for these two samples are also reported. On the basis of these
results, a preliminary phase diagram is presented. Optimum compositional
homogeneity is needed to properly characterize the new monoclinic region.


title: Underlying Pairing States in Cuprate Superconductors

abstract:
  In this Letter, we develop a microscopic theory to describe the close
proximity between the insulating antiferromagnetic (AF) order and the d-wave
superconducting (dSC) order in cuprates. We show that the cuprate ground states
form a configuration of coherent pairing states consisting of extended singlet
Cooper pairs and triplet $\pi$ pairs, which can simultaneously describe AF and
dSC orders.


title:
Phase-diagram and quasiparticles of a lattice SU(2) scalar-fermion model
  in (2+1) dimensions

abstract:
  The phase diagram at zero temperature of a lattice SU(2) scalar-fermion model
in (2+1) dimensions is studied numerically and with Mean-Field methods. Special
attention is devoted to the strong coupling regime. We have developed a new
method to adaptate the Hybrid Monte Carlo algorithm to the O(3) non-linear
$\sigma$ model constraint. The charged excitations in the various phases are
studied at the Mean-Field lev el. Bound states of two charged fermions are
found in a strongly coupled {\it paramagnetic} phase. On the other hand, in the
strongly coupled antiferromagnetic phase fermionic excitations around momenta
$(\pm\frac{\pi}{2},\pm\frac{\pi}{2},\pm\frac{\pi}{2})$ emerge.


title: Sn delta-doping in GaAs

abstract:
  We have prepared a number of GaAs structures delta-doped by Sn using the
well-known molecular beam epitaxy growth technique. The samples obtained for a
wide range of Sn doping densities were characterised by magnetotransport
experiments at low temperatures and in high magnetic fields up to 38 T.
Hall-effect and Shubnikov-de Haas measurements show that the electron densities
reached are higher than for other delta-dopants, like Si and Be. The maximum
carrier density determined by the Hall effect equals 8.4x10^13 cm^-2. For all
samples several Shubnikov-de Haas frequencies were observed, indicating the
population of multiple subbands. The depopulation fields of the subbands were
determined by measuring the magnetoresistance with the magnetic field in the
plane of the delta-layer. The experimental results are in good agreement with
selfconsistent bandstructure calculations. These calculation shows that in the
sample with the highest electron density also the conduction band at the L
point is populated.


title: Knot Theory and the Problem of Classification for Plastic State

abstract:
  In this paper we constructed new model of plastic deformation. The knot
theory was used to classify the plastic state.


title: Mechanism for Surface Waves in Vibrated Granular Material

abstract:
  We use molecular dynamics simulations to study the formation of surface waves
in vertically vibrated granular material. We find that horizontal movements of
particles, which are essential for the formation of the waves, consist of two
distinct processes. First, the movements sharply increase while the particles
are colliding with a bottom plate, where the duration of the collisions is very
short compared to the period of the vibration. Next, the movements gradually
decrease between the collisions, during which the particles move through the
material. We also find that the horizontal velocity field after the collisions
is strongly correlated to the surface profile before the collisions.


title: Resistivity of non-Fermi liquid U2Pt2In under pressure

abstract:
  Non-Fermi liquid behaviour in single-crystalline U2Pt2In has been studied by
means of resistivity experiments (I||c) under hydrostatic pressure (P<1.5 GPa).
At ambient pressure the resistivity rho(T) follows a power law rho~T^alpha with
alpha~0.5. Upon applying pressure alpha increases. For P>1 GPa a minimum
develops in rho(T). A study of the field dependence of the minimum confirms its
magnetic origin. The ratio c/a is proposed as the effective control parameter,
rather than the unit cell volume.


title: Scissors mode and superfluidity of a trapped Bose-Einstein condensed gas

abstract:
  We investigate the oscillation of a dilute atomic gas generated by a sudden
rotation of the confining trap (scissors mode). This oscillation reveals the
effects of superfluidity exhibited by a Bose-Einstein condensate. The scissors
mode is investigated also in a classical gas above T_c in various collisional
regimes. The crucial difference with respect to the superfluid case arises from
the occurence of low frequency components, which are responsible for the rigid
value of the moment of inertia. Different experimental procedures to excite the
scissors mode are discussed.


title: Optimized Effective Potential Method for Polymers

abstract:
  The optimized effective potential (OEP) method allows for calculation of the
local, effective single particle potential of density functional theory for
explicitly orbital-dependent approximations to the exchange-correlation energy
functional. In the present work the OEP method is used together with the
approximation due to Krieger, Li and Iafrate (KLI). We present the first
application of this method to polymers. KLI calculations have been performed
for the insulating polyethylene and the results have been compared to those
from other orbital-dependent potentials. Various properties of the band
structure are also calculated. The single-particle band gap strongly depends on
the basis set with larger basis sets yielding narrow gaps. For the highest
occupied orbital energy the difference is more pronounced. In order to get the
right band gap in OEP the exchange contribution to the derivative discontinuity
is calculated and added to the Kohn-Sham gap.


title: Maximum thickness of a two-dimensional trapped Bose system

abstract:
  The trapped Bose system can be regarded as two-dimensional if the thermal
fluctuation energy is less than the lowest energy in the perpendicular
direction. Under this assumption, we derive an expression for the maximum
thickness of an effective two-dimensional trapped Bose system.


title:
Index Distribution of Random Matrices with an Application to Disordered
  Systems

abstract:
  We compute the distribution of the number of negative eigenvalues (the index)
for an ensemble of Gaussian random matrices, by means of the replica method.
This calculation has important applications in the context of statistical
mechanics of disordered systems, where the second derivative of the potential
energy (the Hessian) is a random matrix whose negative eigenvalues measure the
degree of instability of the energy surface. An analysis of the probability
distribution of the Hessian index is therefore relevant for a geometric
characterization of the energy landscape in disordered systems. The approach we
use here is particularly suitable for this purpose, since it addresses the
problem without any a priori assumption on the random matrix ensemble and can
be naturally extended to more realistic, non-Gaussian distributions.


title: An Empirical Investigation of the Forward Interest Rate Term Structure

abstract:
  In this paper we study empirically the Forward Rate Curve (FRC) of 5
different currencies. We confirm and extend the findings of our previous
investigation of the U.S. Forward Rate Curve. In particular, the average FRC
follows a square-root law, with a prefactor related to the spot volatility,
suggesting a Value-at-Risk like pricing. We find a striking correlation between
the instantaneous FRC and the past spot trend over a certain time horizon, in
agreement with the idea of an extrapolated trend effect. We present a model
which can be adequately calibrated to account for these effects.