title:
Virtual-crystal approximation that works: Locating a composition phase
  boundary in Pb(Zr_{1-x}Ti_3)O_3

abstract:
  We present a new method for modeling disordered solid solutions, based on the
virtual crystal approximation (VCA). The VCA is a tractable way of studying
configurationally disordered systems; traditionally, the potentials which
represent atoms of two or more elements are averaged into a composite atomic
potential. We have overcome significant shortcomings of the standard VCA by
developing a potential which yields averaged atomic properties. We perform the
VCA on a ferroelectric oxide, determining the energy differences between the
high-temperature rhombohedral, low-temperature rhombohedral and tetragonal
phases of Pb(Zr_{1-x}Ti_x)O_3 at x=0.5 and comparing these results to
superlattice calculations and experiment. We then use our new method to
determine the preferred structural phase at x=0.4. We find that the
low-temperature rhombohedral phase becomes the ground state at x=0.4, in
agreement with experimental findings.


title: Numerical Simulation of Macroscopic Traffic Equations

abstract:
  Macroscopic traffic simulations are based on coupled non-linear partial
differential equations, the solutions of which are either shock-like or
inhomogeneous with steep gradients, at least in the interesting density regime.
We discuss several suitable explicit integration schemes, including their
advantages and disadvantages, their numerical robustness and errors. We compare
the effects of diffusion with that of nonlocal terms. In addition, we
investigate different possibilities of treating realistic open boundary
conditions. The theoretical considerations are illuminated by many examples of
simulation results.


title: Asymmetric particle systems on R

abstract:
  We study interacting particle systems on the real line which generalize the
Hammersley process [D. Aldous and P. Diaconis, Prob. Theory Relat. Fields 103,
199-213 (1995)]. Particles jump to the right to a randomly chosen point between
their previous position and that of the forward neighbor, at a rate which may
depend on the distance to the neighbor. A class of models is identified for
which the invariant particle distribution is Poisson. The bulk of the paper is
devoted to a model where the jump rate is constant and the jump length is a
random fraction $r$ of the distance to the forward neighbor, drawn from a
probability density $\phi(r)$ on the unit interval. This is a special case of
the random average process of Ferrari and Fontes [El. J. Prob. 3, Paper no. 6
(1998)]. The discrete time version of the model has been considered previously
in the context of force propagation in granular media [S.N. Coppersmith et al.,
Phys. Rev. E 53, 4673 (1996)]. We show that the stationary two-point function
of particle spacings factorizes for any choice of $\phi(r)$. Under the
assumption that this implies pairwise independence, the invariant density of
interparticle spacings for the case of uniform $\phi(r)$ is found to be a gamma
distribution with parameter $\nu$, where $\nu = 1/2$, 1 and 2 for continuous
time, backward sequential and discrete time dynamics, respectively. A heuristic
derivation of a nonlinear diffusion equation is presented, and the tracer
diffusion coefficient is computed for arbitrary $\phi(r)$ and different types
of dynamics.


title: Andreev Reflection in Strong Magnetic Fields

abstract:
  We have studied the interplay of Andreev reflection and cyclotron motion of
quasiparticles at a superconductor-normal-metal interface with a strong
magnetic field applied parallel to the interface. Bound states are formed due
to the confinement introduced both by the external magnetic field and the
superconducting gap. These bound states are a coherent superposition of
electron and hole edge excitations similar to those realized in finite
quantum-Hall samples. We find the energy spectrum for these Andreev edge states
and calculate transport properties.


title: The periodic Anderson model from the atomic limit and FeSi

abstract:
  The exact Green's functions of the periodic Anderson model for $U\to \infty $
are formally expressed within the cumulant expansion in terms of an effective
cumulant. Here we resort to a calculation in which this quantity is
approximated by the value it takes for the exactly soluble atomic limit of the
same model. In the Kondo region a spectral density is obtained that shows near
the Fermi surface a structure with the properties of the Kondo peak.
Approximate expressions are obtained for the static conductivity $% \sigma (T)$
and magnetic susceptibility $\chi (T)$ of the PAM, and they are employed to fit
the experimental values of FeSi, a compound that behaves like a Kondo insulator
with both quantities vanishing rapidly for $T\to 0$. Assuming that the system
is in the intermediate valence region, it was possible to find good agreement
between theory and experiment for these two properties by employing the same
set of parameters. It is shown that in the present model the hybridization is
responsible for the relaxation mechanism of the conduction electrons.


title:
Crossover behavior for complex order parameter in high-Tc
  superconductors

abstract:
  A number of recent experiments have suggested the presence of either real or
complex components in the gap symmetry of high-$T_c$ superconductors (HTSC). In
this paper we introduce a novel approach to study the competition of such
complex order parameter mixtures by varying the position of the two-body
attractive potential in a two dimensional extended Hubbard Hamiltonian. We show
that this procedure explain a number of experimental results and on the
theoretical side, it may be related with certain HTSC microscopic models like
the spin fluctuation theory. Following current trends we concentrate on the
study of $d_{x^2-y^2}$ order parameter with a component of the type $d_{xy}$ or
a s-wave like $s_{x^2+y^2}$ and $s_{xy}$ symmetry. We show that the position of
the optimal s-component peak changes with the position parameter $b$ while the
d-component occurs always in the optimally region around hole content $\rho
\approx 0.39$.


title:
The extended Hubbard model applied to phase diagram and the pressure
  effects in \Bi superconductors

abstract:
  We use the two dimensional extended Hubbard Hamiltonian with the position of
the attractive potential as a variable parameter with a BCS type approach to
study the interplay between the superconductor transition temperature $T_c$ and
hole content for high temperature superconductors. This novel method gives some
insight on the range and intensity of the Cooper pair interaction and why
different compounds have different values for their measured coherence lengths
and it describes well the experimental results of the superconducting phase
diagram $T_c \times n$. The calculations may also be used to study the effect
of the applied pressure with the assumption that it increases the attractive
potential which is accompanied by an increase in the superconductor gap. In
this way we obtain a microscopic interpretation for the intrinsic term and a
general expansion for $T_c$ in terms of the pressure which reproduces well the
experimental measurements on the \Bi superconductors.


title: Continuous quantum measurement of a double dot

abstract:
  We consider the continuous measurement of a double quantum dot by a weakly
coupled detector (tunnel point contact nearby). While the conventional approach
describes the gradual system decoherence due to the measurement, we study the
situation when the detector output is explicitly recorded that leads to the
opposite effect: gradual purification of the double-dot density matrix.
Nonlinear Langevin equation is derived for the random evolution of the density
matrix which is reflected and caused by the stochastic detector output. Gradual
collapse, gradual purification, and quantum Zeno effect are naturally described
by the equation. We also discuss the possible experiments to confirm the
theory.


title: Scaling and Crossovers in Diffusion Limited Aggregation

abstract:
  We discuss the scaling of characteristic lengths in diffusion limited
aggregation (DLA) clusters in light of recent developments using conformal
maps. We are led to the conjecture that the apparently anomalous scaling of
lengths is due to one slow crossover. This is supported by an analytical
argument for the scaling of the penetration depth of newly arrived random
walkers, and by numerical evidence on the Laurent coefficients which uniquely
determine each cluster. We find a single crossover exponent of -0.3 for all the
characteristic lengths in DLA. This gives a hint about the structure of the
renormalization group for this problem.


title:
Transport properties of strongly correlated metals:a dynamical
  mean-field approach

abstract:
  The temperature dependence of the transport properties of the metallic phase
of a frustrated Hubbard model on the hypercubic lattice at half-filling are
calculated. Dynamical mean-field theory, which maps the Hubbard model onto a
single impurity Anderson model that is solved self-consistently, and becomes
exact in the limit of large dimensionality, is used. As the temperature
increases there is a smooth crossover from coherent Fermi liquid excitations at
low temperatures to incoherent excitations at high temperatures. This crossover
leads to a non-monotonic temperature dependence for the resistance,
thermopower, and Hall coefficient, unlike in conventional metals. The
resistance smoothly increases from a quadratic temperature dependence at low
temperatures to large values which can exceed the Mott-Ioffe-Regel value, hbar
a/e^2 (where "a" is a lattice constant) associated with mean-free paths less
than a lattice constant. Further signatures of the thermal destruction of
quasiparticle excitations are a peak in the thermopower and the absence of a
Drude peak in the optical conductivity. The results presented here are relevant
to a wide range of strongly correlated metals, including transition metal
oxides, strontium ruthenates, and organic metals.


title: Polarizability of 2D monster and light scattering

abstract:
  The electrostatics of 2D system with complicated inner boundary is studied.
The object which we call "monster" is built by an iterative process of multiple
conformal mapping of the circle exterior. The procedure leads to the figures
built from circle with branching curved cuts (i), to the multiple tangential
near-round circles (ii) and the Mandelbrot map (iii). The polarizability of a
monster in the homogeneous external field is found. The light scattering
cross-section was expressed through the polarizability of a monster.


title: BCS to Bose Crossover in Anisotropic Superconductors

abstract:
  In this work we use functional integral techniques to examine the nearest
neighbour attractive Hubbard model on a quasi-2D lattice. It is a simple
phenomenological model for the high-Tc cuprates that allows both extended
(non-local) s- and d-wave singlet superconductivity as well as mixed symmetry
states. The Hartree-Gor'kov mean field theory of the model has a finite
temperature phase diagram which shows a transition from pure s-wave to pure
d-wave superconductivity, via a mixed symmetry s+id state, as a function of
doping. Including Gaussian fluctuations we examine the crossover from
weak-coupling BCS superconductivity to the strong-coupling Bose-Einstein
condensation of composite s- or d-wave bosons and comment on the origin and
symmetry of the pseudogap.


title: Systematic low temperature expansion in Ginzburg - Landau model

abstract:
  Consistent perturbation theory for thermodynamical quantities in strongly
type II superconductors in magnetic field at low temperatures is developed. It
is complementary to the existing expansion valid at high temperatures.
Magnetization and specific heat are calculated to two loop order and compare
well with existing Monte Carlo simulations, other theories and experiments.


title: The superconducting phase transition and gauge dependence

abstract:
  The gauge dependence of the renormalization group functions of the
Ginzburg-Landau model is investigated. The analysis is done by means of the
Ward-Takahashi identities. After defining the local superconducting order
parameter, it is shown that its exponent $\beta$ is in fact gauge independent.
This happens because in $d=3$ the Landau gauge is the only gauge having a
physical meaning, a property not shared by the four-dimensional model where any
gauge choice is possible. The analysis is done in both the context of the
$\epsilon$-expansion and in the fixed dimension approach. It is pointed out the
differences that arise in both of these approaches concerning the gauge
dependence.


title:
Effective Dimensionality and Band Structure of alpha-Nav_2o_5 Compound:
  1D or 2D?

abstract:
  The AV_nO_{2n+1} mixed valence compounds (n=1, A=Na) are classified as
dimerized layered system with strongly interacting d-electrons of vanadium
ions. The derived band gaps, energy dispersion relations and density of
electronic states are in a good agreement with available experimental and
theoretical data. The correlated band gap provides the insulating state of the
high-temperature alpha-NaV_2O_5 phase whereas the state, earlier misrepresented
as the spin-Peierls state, is governed, in fact, by opening of the Coulomb gap.


title: Closed form results for shape transitions in lipid monolayer domains

abstract:
  Isolated domains in lipid monolayers exhibit shape transitions as a
consequence of the competing effects of line tension and long-range dipolar
interactions. Nontrivial integrals ultimately arise in instability analysis
calculations of these domains. In this work we present a closed form evaluation
of such integrals in terms of associated Legendre functions. Our approach is
motivated by and extends the work of J. M. Deutch and F. E. Low (J. Phys.
Chem., 1992, 96, 7097-7101). Our closed form solutions lead to simpler analytic
expressions for stability thresholds, which are easier to evaluate explicitly.
Relevant asymptotic behavior is calculated in various limits of interest. For
the case of Coulomb interactions, a general closed form expression is obtained
for the critical domain radii.


title:
Acceleration effect caused by the Onsager reaction term in a frustrated
  coupled oscillator system

abstract:
  The role of the Onsager reaction term (ORT) is not yet well understood in
frustrated coupled oscillator systems, since the Thouless-Anderson-Palmer (TAP)
and replica methods cannot be directly applied to these non-equilibrium
systems. In this paper, we consider two oscillator associative memory models,
one with symmetric and one with asymmetric dilution of coupling. These two
systems are ideal for evaluating the effect of the ORT, because, with the
exception of the ORT, they have the same order parameter equations. We found
that the two systems have identical macroscopic properties, except for the
acceleration effect caused by the ORT. This acceleration effect does not exist
in any equilibrium system.


title: 89Y NMR Probe of Zn Induced Local Magnetism in YBa2(Cu(1-y)Zn(y))3O(6+x)

abstract:
  We present detailed data and analysis of the effects of Zn substitution on
the planar Cu site in YBa$_2$Cu$_3$O$_{6+x}$ (YBCO$_{6+x}$) as evidenced from
our $^{89}$Y NMR measurements on oriented powders. For $x<<1$ we find
additional NMR lines which are associated with the Zn substitution. From our
data on the intensities and temperature dependence of the shift, width, and
spin-lattice relaxation rate of these resonances, we conclude that the spinless
Zn 3$d$$^{10}$ state induces local moments on the near-neighbour ($% nn$) Cu
atoms. Additionally, we conjecture that the local moments actually extend to
the farther Cu atoms with the magnetization alternating in sign at subsequent
$nn$ sites. We show that this analysis is compatible with ESR data taken on
dilute Gd doped (on the Y site) and on neutron scattering data reported
recently on Zn substituted YBCO$_{6 + x}$. For optimally doped compounds
$^{89}$Y $nn$ resonances are not detected, but a large $T$% -dependent
contribution to the $^{89}$Y NMR linewidth is evidenced and is also attributed
to the occurence of a weak induced local moment near the Zn. These results are
compatible with macroscopic magnetic measurements performed on YBCO$_{6 + x}$
samples prepared specifically in order to minimize the content of impurity
phases. We find significant differences between the present results on the
underdoped YBCO$_{6 + x}$ samples and $% ^{27}$Al NMR data taken on Al$^{3+}$
substituted on the Cu site in optimally doped La$_2$CuO$_4$. Further
experimental work is needed to clarify the detailed evolution of the impurity
induced magnetism with hole content in the cuprates.


title: High-frequency dynamics of wave localisation

abstract:
  We study the effect of localisation on the propagation of a pulse through a
multi-mode disordered waveguide. The correlator <u(omega1)u*(omega2)> of the
transmitted wave amplitude u at two frequencies differing by delta_omega has
for large delta_omega the stretched exponential tail ~exp(-sqrt{tau_D
delta_omega/2}). The time constant tau_D=L^2/D is given by the diffusion
coefficient D, even if the length L of the waveguide is much greater than the
localisation length xi. Localisation has the effect of multiplying the
correlator by a frequency-independent factor exp(-L/2xi), which disappears upon
breaking time-reversal symmetry.


title: Wave Function Mismatches and Coulomb Drag

abstract:
  In this paper, I study the topological excitations in a pairing state in
double layer systems at Landau level filling factor $\nu=1/2$ in the presence
of disorders. Due to mismatches between single particle wave functions of
composite Fermions in different layers, the sensitivity of the Chern number of
the pairing state, with respect to changes of impurities, is infinity.
Consequently, Goldstone mode in this pairing state is strongly damped at low
temperature. It is argued that this leads to a unique temperature dependence of
the drag resistance at low temperature.


title:
Finite Range Model Interaction Potential for d-wave Superconductors: Tc
  vs. Doping in the Cuprates

abstract:
  We study a simple BCS-like model which describes unconventional
superconductivity on the basis of an electron-electron attraction corresponding
to the delta-shell potential: $U(r) = -g \delta(r-r_0)$. It predicts a $T_c$
vs. doping behavior similar to that characteristic of the High-$T_c$ cuprates.


title: A thermostable trilayer resist for niobium lift-off

abstract:
  We have developped a novel lift-off process for fabrication of high quality
superconducting submicron niobium structures. The process makes use of a
thermostable polymer with a high transition temperature T_{g}= 235 C and an
excellent chemical stability. The superconducting critical temperature of 100
nm wide niobium lines is above 7 K. An example of shadow evaporation of a Nb-Cu
submicron hybrid structure is given. A potential application of this process is
the fabrication of very small single electron devices using refratory metals.


title: Semi-microscopic theory of elasticity near the vulcanization transition

abstract:
  Randomly crosslinked macromolecules undergo a liquid-to-amorphous solid phase
transition at a critical crosslink concentration. This transition has two main
signatures: the random localization of a fraction of the monomers and the
emergence of a nonzero static shear modulus. In this article, a
semi-microscopic statistical mechanical theory of the elastic properties of the
amorphous solid state is developed. This theory takes into account both
quenched disorder and thermal fluctuations, and allows for the direct
computation of the free energy change of the sample due to a given macroscopic
shear strain. This leads to an unambiguous determination of the static shear
modulus. At the level of mean field theory, it is found (i) that the shear
modulus grows continuously from zero at the transition, and does so with the
classical exponent, i.e., with the third power of the excess crosslink density
and, quite surprisingly, (ii) that near the transition the external stresses do
not spoil the spherical symmetry of the localization clouds of the particles.


title: A Fast Algorithm for Generating Long Self-Affine Profiles

abstract:
  We introduce a fast algorithm for generating long self-affine profiles. The
algorithm, which is based on the fast wavelet transform, is faster than the
conventional Fourier filtering algorithm. In addition to increased performance
for large systems, the algorithm, named the wavelet filtering algorithm, a
priori gives rise to profiles for which the long-range correlation extends
throughout the entire system independently of the length scale.


title:
A simple classical mapping of the spin-polarized quantum electron gas:
  distribution functions and local field corrections

abstract:
  We use the now well known spin-unpolarized exchange-correlation energy E_{xc}
of the uniform electron gas as the basic ``many-body'' input to determine the
temperature T_q of a classical Coulomb fluid having the same correlation energy
as the quantum system. It is shown that the spin-polarized pair distribution
functions (SPDFs) of the classical fluid at T_q, obtained using the
hyper-netted chain (HNC) equation are in excellent agreement with those of the
T=0 quantum fluid obtained by quantum Monte Carlo (QMC) simulations. These
methods are computationally simple and easily applied to problems which are
currently outside the scope of QMC. Results are presented for the SPDFs and the
local-field corrections to the response functions of the electron fluid at zero
and finite temperatures.


title: Order parameter suppression in double layer quantum Hall ferromagnets

abstract:
  Double-layer quantum Hall systems at Landau level filling factor $\nu=1$ have
a broken symmetry ground state with spontaneous interlayer phase coherence and
a gap between symmetric and antisymmetric subbands in the absence of interlayer
tunneling. We examine the influence of quantum fluctuations on the spectral
function of the symmetric Green's function, probed in optical absorption
experiments (cond-mat/9809373). We find that as the maximum layer separation at
which the $\nu=1$ quantum Hall effect occurs is approached, absorption in the
lowest Landau level grows in strength. Detailed line shapes for this absorption
are evaluated and related to features in the system's collective excitation
spectrum.


title: Multicomponent nonisothermal nucleation. 1. Kinetic equation

abstract:
  The first part of the theory for the multicomponent nonisothermal nucleation
is presented. On the base of analysis of the elementary acts of interation
between an embryo and environment the kinetic equation is derived. This
equation will be solved later and gives the nucleation rate for nonisothermal
nucleation in the system with many condensating components. The orders of
operators in this equation are estimated.


title:
Observation of Kosterlitz-Thouless spin correlations in the colossally
  magnetoresistive layered manganite $La_{1.2}Sr_{1.8}Mn_{2}O_{7}$

abstract:
  The spin correlations of the bilayer manganite $La_{1.2}Sr_{1.8}Mn_{2}O_{7}$
have been studied using neutron scattering. On cooling within the paramagnetic
state, we observe purely two-dimensional behavior with a crossover to
three-dimensional scaling close to the ferromagnetic transition. Below $T_C$,
an effective finite size behavior is observed. The quantitative agreement of
these observations with the conventional quasi two-dimensional
Kosterlitz-Thouless model indicates that the phase transition is driven by the
growth of magnetic correlations, which are only weakly coupled to polarons
above $T_C$.


title: Multicomponent nonisothermal nucleation. 2. Chapman-Enskog procedure

abstract:
  The second part of the theory for the multicomponent nonisothermal nucleation
is presented. The solution of the kinetic equation already derived in the first
part is given with the help of the Chapman-Enskog procedure. At first the
relaxation stage is considered. The special choice of the relaxation operator
allows to refuse from the special small parameter usually required in the
nucleation problems. The special procedure allows to estimate the tails of the
approximations appeared in the reccurent procedures. The final formulas for
corrections allows to reduce the problem to the ordinary Fokker-Planck equation
in the nulticomponent case.


title:
The monoclinic phase of PZT ceramics: Raman and phenomenological theory
  studies

abstract:
  This work reports on the first Raman detection of the tetragonal to
monoclinic phase transition in PZT ceramics near morphotropic phase boundary at
low temperatures. The transition is characterized by changes in the frequency
of lattice modes with the temperature. The results presented here confirm the
previous one recently reported by Noheda et al. using high-resolution
synchrotron X-ray powder diffraction technique and dielectric measurements. The
stability of the new phase is discussed within the framework of
phenomenological Landau-Devonshire Theory.


title: Multicomponent nonisothermal nucleation. 3. Numerical results

abstract:
  The final (third) part of the theory gives the results of numerical
calculations according to the formulas derived in the previous two parts. Also
the comparison with the already published theories is given. Some conclusions
connected with the qualitative picture of the nucleation process are presented.


title: Kondo time scales for quantum dots - response to pulsed bias potentials

abstract:
  The response of a quantum dot in the Kondo regime to rectangular pulsed bias
potentials of various strengths and durations is studied theoretically. It is
found that the rise time is faster than the fall time, and also faster than
time scales normally associated with the Kondo problem. For larger values of
the pulsed bias, one can induce dramatic oscillations in the induced current
with a frequency approximating the splitting between the Kondo peaks that would
be present in steady state. The effect persists in the total charge transported
per pulse, which should facilitate the experimental observation of the
phenomenon.


title: Mesoscopic mechanism of exchange interaction in magnetic multilayers

abstract:
  We discuss a mesoscopic mechanism of exchange interaction in
ferromagnet-normal metal-ferromagnet multilayers. We show that in the case when
the metal's thickness is larger than the electron mean free path, the relative
orientation of magnetizations in the ferromagnets is perpendicular. The
exchange energy between ferromagnets decays with the metal thickness as a power
law.


title: Critical States in a Dissipative Sandpile Model

abstract:
  A directed dissipative sandpile model is studied in the two-dimension.
Numerical results indicate that the long time steady states of this model are
critical when grains are dropped only at the top or, everywhere. The critical
behaviour is mean-field like. We discuss the role of infinite avalanches of
dissipative models in periodic systems in determining the critical behaviour of
same models in open systems.


title:
Random matrix model for quantum dots with interactions and the
  conductance peak spacing distribution

abstract:
  We introduce a random interaction matrix model (RIMM) for finite-size
strongly interacting fermionic systems whose single-particle dynamics is
chaotic. The model is applied to Coulomb blockade quantum dots with irregular
shape to describe the crossover of the peak spacing distribution from a
Wigner-Dyson to a Gaussian-like distribution. The crossover is universal within
the random matrix model and is shown to depend on a single parameter: a scaled
fluctuation width of the interaction matrix elements. The crossover observed in
the RIMM is compared with the results of an Anderson model with Coulomb
interactions.


title:
Suppression of Ground-State Magnetization in Finite-Sized Systems Due to
  Off-Diagonal Interaction Fluctuations

abstract:
  We study a generic model of interacting fermions in a finite-sized disordered
system. We show that the off-diagonal interaction matrix elements induce
density of states fluctuations which generically favor a minimum spin ground
state at large interaction amplitude, $U$. This effect competes with the
exchange effect which favors large magnetization at large $U$, and it
suppresses this exchange magnetization in a large parameter range. When
off-diagonal fluctuations dominate, the model predicts a spin gap which is
larger for odd-spin ground states as for even-spin, suggesting a simple
experimental signature of this off-diagonal effect in Coulomb blockade
transport measurements.

categories: cond-mat.mes-hall cond-mat.str-el nlin.CD nucl-th


title: Bethe Ansatz solution of triangular trimers on the triangular lattice

abstract:
  Details are presented of a recently announced exact solution of a model
consisting of triangular trimers covering the triangular lattice. The solution
involves a coordinate Bethe Ansatz with two kinds of particles. It is similar
to that of the square-triangle random tiling model, due to M. Widom and P. A.
Kalugin. The connection of the trimer model with related solvable models is
discussed.


title: Bosonization and Strongly Correlated Systems

abstract:
  This volume provides a detailed account of bosonization. The first part of
the book examines the technical aspects of bosonization including
one-dimensional fermions, the Gaussian model, the structure of Hilbert space in
conformal theories, Bose-Einstein condensation in two dimensions, non-Abelian
bosonization, and the Ising and WZNW models. The second part presents
applications of the bosonization technique to realistic models including the
Tomonaga-Luttinger liquid, spin liquids in one dimension and the spin-1/2
Heisenberg chain with alternative exchange. The third part addresses the
problems of quantum impurities. Chapters cover potential scattering, the X-ray
edge problem, impurities in Tomonaga-Luttinger liquids and the multi-channel
Kondo problem.


title:
Self-Trapping, Quantum Tunneling and Decay Rates for a Bose Gas with
  Attractive Nonlocal Interaction

abstract:
  We study the Bose-Einstein condensation for a cloud of $^7$Li atoms with
attractive nonlocal (finite-range) interaction in a harmonic trap. In addition
to the low-density metastable branch, that is present also in the case of local
interaction, a new stable branch appears at higher densities. For a large
number of atoms, the size of the cloud in the stable high-density branch is
independent of the trap size and the atoms are in a macroscopic quantum
self-trapped configuration. We analyze the macroscopic quantum tunneling
between the low-density metastable branch and the high-density one by using the
istanton technique. Moreover we consider the decay rate of the Bose condensate
due to inelastic two- and three-body collisions.


title: Wigner Crystalline Edges in nu < 1 Quantum Dots

abstract:
  We investigate the edge reconstruction phenomenon believed to occur in
quantum dots in the quantum Hall regime when the filling fraction is nu < 1.
Our approach involves the examination of large dots (< 40 electrons) using a
partial diagonalization technique in which the occupancies of the deep interior
orbitals are frozen. To interpret the results of this calculation, we evaluate
the overlap between the diagonalized ground state and a set of trial
wavefunctions which we call projected necklace (PN) states. A PN state is
simply the angular momentum projection of a maximum density droplet surrounded
by a ring of localized electrons. Our calculations reveal that PN states have
up to 99% overlap with the diagonalized ground states, and are lower in energy
than the states identified in Chamon and Wen's study of the edge
reconstruction.


title:
Observation of a Universial Low Temperature Limit of the Free Flux Flow
  Resistivity in Superclean Bi_2Sr_2CaCu_2O_8 Whiskers

abstract:
  We report peculiar vortex motion in clean Bi$_2$Sr$_2$CaCu$_2$O$_8$ single
crystals, which reveals nearly linear-$T$ resistivity tails extending to low
temperatures. The resistivity was found to satisfy the classical
Bardeen-Stephen model for free flux flow, which is otherwise hard to observe
under normal experimental conditions in high-$T_c$ cuprates. Moreover, in the
superclean regime, a universal temperature-independent value for the flux flow
resistivity was observed, $\rho_f = 1.4(B-B^*)$. We interpret this
carrier-relaxation {\it independent} behavior as being related to the
dissipation caused by the minigap states within the vortex core. The results
are in agreement with theoretical calculations (N. B. Kopnin and G. E. Volovik,
Phys. Rev. Lett. {\bf 79}, 1377 (1997)).


title: Supersymmetric spin operators

abstract:
  We develop a supersymmetric representation of spin operators which unifies
the Schwinger and Abrikosov representations of SU(N) spin operators, allowing a
second-quantized treatment of representations of the SU(N) group with both
symmetric and antisymmetric character. By applying this to the SU(N) Kondo
model, we show that it is possible to develop a controlled treatment of both
Magnetism and the Kondo effect within a single large N expansion.


title: The ground state of the two-dimensional Hubbard model

abstract:
  We have studied the ground state of the two-dimensional Hubbard model by
using the adaptive sampling quantum monte carlo method. We found enhancement of
the d-wave correlation function, the spin gap and the coexistence of both the
commensurate and incommensurate peaks in $S(\vec{q})$, which does not
contradict a recent experimental finding that both the resonance peak and the
incommensurate peaks reside in the same doping level of YBCO and BSCCO.


title:
Effect of short-range electron correlations in dynamic transport in a
  Luttinger liquid

abstract:
  The density operator in the Luttinger model consists of two components, one
of which describes long-wave fluctuations and the other is related to the rapid
oscillations of the charge-density-wave (CDW) type, caused by short-range
electron correlations. It is commonly believed that the conductance is
determined by the long-wave component. The CDW component is considered only
when an impurity is present. We investigate the contribution of this component
to the dynamic density response of a Luttinger liquid free from impurities. We
show that the conventional form of the CDW density operator does not conserve
the number of particles in the system. We propose the corrected CDW density
operator devoid of this shortcoming and calculate the dissipative conductance
in the case when the one-dimensional conductor is locally disturbed by a
conducting probe. The contribution of the CDW component to conductance is found
to dominate over that of the long-wave component in the low-frequency regime.


title:
Growth and characterization of BiSCCO 2212 whiskers from melts
  containing various La contents

abstract:
  Bi2Sr2-xLaxCaCu2O8+d superconducting whiskers were successfully grown from
Bi-rich meltscontaining various La contents. Effect of La-doping on the whisker
growth, structure and superconductivity has been studied. It has been found
that the whiskers can be grown only from La-doped melts, no whisker was
obtained from the La-free melt x=0. Within the doping region x=0.025-0.3, all
the grown whiskers are of the Bi-2212 pure phase. The c-axis lattice constant
decreases with increasing the La content in the melt. The effect of La doping
on the superconductivity is similar to that of other rare earth dopings in this
system, it depresses and broadens the transition. The melt method used in this
letter is compared with the other two kinds of processes used so far, usual
powder sintering and glassy precursor annealing method. The possible growth
mechanism of the whiskers from the melt method is discussed briefly.


title: Effect of La-doping on growth and superconductivity of Bi-2212 crystals

abstract:
  Single crystals of the layered superconductor Bi2Sr2(Ca1-xLax)Cu2O8+d were
successfully grown out by a self-flux method. Upon La-doping, the c-axis
contracts but the structure remains stable up to the critical concentration xc,
above which the crystals contain the pure Bi2(Sr,La)2CuO6 phase. The reduction
of the superconducting transition temperature follows a linear relation,
Tc(x)=Tc(0) (1-x/xc), with xc=0.3 being consistent with the structure data.
This and a comparison with literature data on Pr3+- (xc>>0.65) and Y3+-doping
(xc=1) indicate an intimate relation between structural and superconducting
stability in the 2212 phase. Besides the widely discussed hole-filling effect,
the structural instability due to the substitution of large La3+ for Ca2+ is
considered to be another contribution to Tc suppression in this system.


title: Effective potential for the reaction-diffusion-decay system

abstract:
  In previous work [cond-mat/9904207,cond-mat/9904215] we have developed a
general method for casting stochastic partial differential equations (SPDEs)
into a functional integral formalism, and have derived the one-loop effective
potential for these systems. In this paper we apply the same formalism to a
specific field theory of considerable interest, the reaction-diffusion-decay
system. When this field theory is subject to white noise we can calculate the
one-loop effective potential (for arbitrary polynomial reaction kinetics) and
show that it is one-loop ultraviolet renormalizable in 1, 2, and 3 space
dimensions. For specific choices of interaction terms the one-loop
renormalizability can be extended to higher dimensions. We also show how to
include the effects of fluctuations in the study of pattern formation away from
equilibrium, and conclude that noise affects the stability of the system in a
way which is calculable.

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


title: Soliton regime in the model with no Lifshitz invariant

abstract:
  Nonlinear properties of the order parameter modulation wave in such systems
as thiourea are described in the framework of the phenomenological model with
no Lifshitz invariant. It is also shown that for some values of the
thermodynamic potential parameters the lock-in transition is continuous in the
type II systems. Close to this transition the soliton lattice appears.


title:
Effect of localized holes on the long-range order in bilayer
  antiferromagnets

abstract:
  The effect of localized holes on the long-range antiferromagnetic order in
bilayer cuprates is studied, by applying the renormalization group to the
appropriate non-linear sigma model. The theory accounts quantitatively for the
magnetic phase diagram of Ca doepd YBa_2Cu_3O_6.


title: Low-Energy Spin Dynamics of CuO Chains in YBa(2)Cu(3)O(6+x)

abstract:
  We study the spin fluctuation dynamics of Cu-O chains in the oxygen deficient
planes of YBa(2)Cu(3)O(6+x). The chains are described by a model including
antiferromagnetic interactions between the spins and Kondo-like scattering of
the oxygen holes by the copper spins. There are incommensurate spin
fluctuations along the direction of the chains. The dynamic structure factor of
this system is qualitatively different from that of a quasi one-dimensional
localized antiferromagnet due to the presence of itinerant holes. We compute
the dynamic structure factor that could be measured in neutron scattering
experiments.


title: Revealing of the simplest mechanisms of a structure formation

abstract:
  In this paper, results of investigations of the simplest mechanisms of a
structure formation are presented. In frameworks of the suggested model the
main attention was focused on such characteristics as wiring of the system,
clusters formation, dynamics of the wiring. The idea to take into account an
influence of the environment factor is employed in the proposed model.
Investigations of systems with such principle of a structure formation reveal
that the system's dynamics has typical features of self-organized criticality
phenomenon. In the avalanche-like processes, which occur in the wiring
dynamics, a power law was found with the index close to 1.4. It is independent
on the environment factor (which in a sense can be considered as system
parameter). The system wiring is approximated pretty well by the Gaussian
distribution. The size of the system does not play any role in the dynamics of
the model.


title:
Influence of a Structure on System's Dynamics on Example of Boolean
  Networks

abstract:
  In this work we study the Boolean Networks of different geometric shape and
lattice organization. It was revealed that no only a spatial shape but also
type of lattice are very important for definition of the structure-dynamics
relation. The regular structures do not give a critical regime in the
investigated cases. Hierarchy together with the irregular structure reveals
characteristic features of criticality.


title: Frequency scaling of photo-induced tunneling

abstract:
  The DC current-voltage characteristics, induced by a driving electric field
with frequency Omega, of a one dimensional electron channel with a tunnel
barrier is calculated. Electron-electron interaction of finite-range is taken
into account. For intermediate interaction strengths, the non-linear
differential conductance shows cusp-like minima at bias voltages integer
multiples of hbar Omega / e that are a consequence of the finite non-zero range
of the interaction but are independent of the shape of the driving electric
field. However, the frequency-scaling of the photo-induced current shows a
cross-over between Omega^{-1} and Omega^{-2}, and depends on the spatial shape
of the driving field and the range of the interaction.


title: Green's Functions in Non-hermitian Random Matrix Models

abstract:
  We review some recent techniques for dealing with non-hermitian random matrix
models based on generalized Green's functions. We introduce the diagrammatic
methods in the hermitian case and generalize them to the non-hermitian case.
The results are illustrated in terms of the eigenvalue distribution,
eigenvector statistics and addition laws.


title:
Superconductivity in sintered-polycristalline
  PrBa$_{2}$Cu$_{3}$O$_{7-\delta}$

abstract:
  Superconductivity in thin films and powders, and in single crystals of Pr-123
has been found by Blackstead et al. and Zou et al., respectively. Nevertheless,
up to now it has never been reported in sintered-policrystalline samples. We
have prepared high-quality samples of this material by following a sol-gel
method.
  We characterized the structure of all samples by using XRD and SEM-EDS
techniques. Magnetic characterization was performed by measuring the
magnetization as a function of the temperature T, and the applied magnetic
field H. Measurements were taken in the ranges 2 K <T < 400 K and 0 <H< 5
Tesla. In this work we report by the first time superconductivity in Pr-123
sintered-polycristalline samples, with $T{_c}$ around 90 K, and $H{_c1}$ around
870 Oe.


title:
Stability of a cubic fixed point in three dimensions. Critical exponents
  for generic N

abstract:
  The detailed analysis of the global structure of the renormalization-group
(RG) flow diagram for a model with isotropic and cubic interactions is carried
out in the framework of the massive field theory directly in three dimensions
(3D) within an assumption of isotropic exchange. Perturbative expansions for RG
functions are calculated for arbitrary $N$ up to the four-loop order and
resummed by means of the generalized Pad$\acute{\rm e}$-Borel-Leroy technique.
Coordinates and stability matrix eigenvalues for the cubic fixed point are
found under the optimal value of the transformation parameter. Critical
dimensionality of the model is proved to be equal to $N_c=2.89 \pm 0.02$ that
agrees well with the estimate obtained on the basis of the five-loop
$\ve$-expansion [H. Kleinert and V. Schulte-Frohlinde, Phys. Lett. B342, 284
(1995)] resummed by the above method. As a consequence, the cubic fixed point
should be stable in 3D for $N\ge3$, and the critical exponents controlling
phase transitions in three-dimensional magnets should belong to the cubic
universality class. The critical behavior of the random Ising model being the
nontrivial particular case of the cubic model when N=0 is also investigated.
For all physical quantities of interest the most accurate numerical estimates
with their error bounds are obtained. The results achieved in the work are
discussed along with the predictions given by other theoretical approaches and
experimental data.

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


title: Absence of the liquid phase when the attraction is not pairwise additive

abstract:
  Recent work on charged colloidal suspensions with very low levels of added
salt has suggested that although pairs of the colloidal particles repel,
clusters of the particles attract. Motivated by this, we study simple model
particles which have many-body attractions. These attractions are generic
many-body attractions and are not calculated for any specific colloidal
suspension. We find that many-body attractions can stabilise solid phases at
low pressures but that the liquid phase is either completely absent from the
equilibrium phase diagram or present only within a small region of parameter
space


title:
Extended bound states of fermions on 2D square lattice beyond the nn
  hopping and interactions

abstract:
  We examine extended bound states in the dilute limit of the extended Hubbard
model with next-nearest-neighbour (nnn) hopping and nnn interactions on the two
dimensional square lattice. By the exact solution of a two-body problem we show
that d-wave pairing is strongly favored by the nnn hopping. We determine the
binding energies, mobilities and dispersion curves across Brillouin zone (B.z.)
for bound states of various symmetries. The numerical analysis shows that the
deep bound states can exist in the whole B.z. and we have also found s*-d
mixing of the bound states.


title: Constrained Path Monte Carlo For Fermions

abstract:
  This article contains lecture notes on the constrained path Monte Carlo
method and its applications to study the Hubbard model. The lectures were given
at the NATO Advanced Summer Institute held in Ithaca NY (1998). The article is
published as a chapter in the book `Quantum Monte Carlo Methods in Physics and
Chemistry,' Ed. M.P. Nightingale and C.J. Umrigar (Kluwer Academic Publishers,
1999).


title: Finite-Temperature Monte Carlo Calculations For Systems With Fermions

abstract:
  We present a quantum Monte Carlo method which allows calculations on
many-fermion systems at finite temperatures without any sign decay. This
enables simulations of the grand-canonical ensemble at large system sizes and
low temperatures. Both diagonal and off-diagonal expectations can be computed
straightforwardly. The sign decay is eliminated by a constraint on the fermion
determinant. The algorithm is approximate. Tests on the Hubbard model show that
accurate results on the energy and correlation functions can be obtained.


title: Hysteresis and Spikes in the Quantum Hall Effect

abstract:
  We observe sharp peaks and strong hysteresis in the electronic transport of a
two-dimensional electron gas (2DEG) in the region of the integral quantum Hall
effect. The peaks decay on time scales ranging from several minutes to more
than an hour. Momentary grounding of some of the contacts can vastly modify the
strength of the peaks. All these features disappear under application of a
negative bias voltage to the backside of the specimen. We conclude, that a
conduction channel parallel to the high mobility 2DEG is the origin for the
peaks and their hysteretic behavior.


title:
Excitation Spectra of Structurally Dimerized and Spin-Peierls Chains in
  a Magnetic Field

abstract:
  The dynamical spin structure factor and the Raman response are calculated for
structurally dimerized and spin-Peierls chains in a magnetic field, using exact
diagonalization techniques. In both cases there is a spin liquid phase composed
of interacting singlet dimers at small fields h < h_c1, an incommensurate
regime (h_c1 < h < h_c2) in which the modulation of the triplet excitation
spectra adapts to the applied field, and a fully spin polarized phase above an
upper critical field h_c2. For structurally dimerized chains, the spin gap
closes in the incommensurate phase, whereas spin-Peierls chains remain gapped.
In the spin liquid regimes, the dominant feature of the triplet spectra is a
one-magnon bound state, separated from a continuum of states at higher
energies. There are also indications of a singlet bound state above the
one-magnon triplet.


title: Asymptotic Distribution of Eigenvalues for a Self-Affine String

abstract:
  We consider a string with fixed endpoints where the mass density and/or the
elastic coefficient vary in a self-affine way as function of position. It is
demonstrated how the eigenvalues in the asymptotic limit are distributed.
Scaling laws for the Weyl term of the asymptotic integrated density of states
is established and confirmed numerically.


title: Heisenberg Spins on a Cylinder Section

abstract:
  Classical Heisenberg spins in the continuum limit (i.e. the nonlinear
sigma-model) are studied on an elastic cylinder section with homogeneous
boundary conditions. The latter may serve as a physical realization of
magnetically coated microtubules and cylindrical membranes. The corresponding
rigid cylinder model exhibits topological soliton configurations with
geometrical frustration due to the finite length of the cylinder section.
Assuming small and smooth deformations allows to find shapes of the elastic
support by relaxing the rigidity constraint: an inhomogeneous Lam\'e equation
arises. Finally, this leads to a novel geometric effect: a global shrinking of
the cylinder section with swellings.


title: Edge Modes Waves in Superlattices in Quantum Hall Effect Regime

abstract:
  The wave propagation of edge modes in a superlattice of 2D electron Gases in
quantum Hall regime is investigated. After introducing surfaces charge and
current densities at the edge, the Maxwell equations are solved for waves
running along the boundary. The constitutive relations expressing the edge
charge and current densities in terms of the fields at the boundary are
derived. One of them is similar to the London equation for superconductor
currents. The dispersion relation and wave polarizations for the momenta region
$w/c<k$ are also obtained for propagation along the borderlines of the electron
gases. It follows that the modes have no dispersion at any frequency. The
static limit solutions complete the definition at the boundary of the formerly
determined interior field configurations showing a Meissner like effect. The
results underline that various of the current theoretical approaches to edge
excitations could be appropriate for superlattice structures but can fail to
describe standard planar samples.


title: Kramers-Wannier Approximation for 3D Ising Model

abstract:
  We investigate the Kramers-Wannier approximation for the three-dimensional
(3D) Ising model. The variational state is represented by an effective 2D Ising
model, which contains two variational parameters. We numerically calculate the
variational partition function using the corner transfer matrix renormalization
group (CTMRG) method, and find its maximum with respect to the variational
parameters. The calculated transition point $K_{\rm c} = 0.2184$ is only 1.5%
less than the true $K_{\rm c}$; the result is better than that obtained by the
corner transfer tensor renormalization group (CTTRG) approach. The calculated
phase transition is mean-field like.


title:
Josephson current in unconventional superconductors through an Anderson
  impurity

abstract:
  Josephson current for a system consisting of an Anderson impurity weakly
coupled to two unconventional superconductors is studied and shown to be driven
by a surface zero energy (mid-gap) bound-state. The repulsive Coulomb
interaction in the dot can turn a $\pi$ junction into a 0-junction. This effect
is more pronounced in p-wave superconductors while in high-temperature
superconductors with $d_{x^2-y^2}$ symmetry it can exit for rather large
artificial centers at which tunneling occurs within a finite region.


title: Progress in Monte Carlo calculations of Fermi systems: normal liquid 3He

abstract:
  The application of the diffusion Monte Carlo method to a strongly interacting
Fermi system as normal liquid $^3$He is explored. We show that the fixed-node
method together with the released-node technique and a systematic method to
analytically improve the nodal surface constitute an efficient strategy to
improve the calculation up to a desired accuracy. This methodology shows
unambiguously that backflow correlations, when properly optimized, are enough
to generate an equation of state of liquid $^3$He in excellent agreement with
experimental data from equilibrium up to freezing.


title: Semiclassical Theory of Integrable and Rough Andreev Billiards

abstract:
  We study the effect on the density of states in mesoscopic ballistic
billiards to which a superconducting lead is attached. The expression for the
density of states is derived in the semiclassical S-matrix formalism shedding
insight into the origin of the differences between the semiclassical theory and
the corresponding result derived from random matrix models. Applications to a
square billiard geometry and billiards with boundary roughness are discussed.
The saturation of the quasiparticle excitation spectrum is related to the
classical dynamics of the billiard. The influence of weak magnetic fields on
the proximity effect in rough Andreev billiards is discussed and an analytical
formula is derived. The semiclassical theory provides an interpretation for the
suppression of the proximity effect in the presence of magnetic fields as a
coherence effect of time reversed trajectories, similar to the weak
localisation correction of the magneto-resistance in chaotic mesoscopic
systems. The semiclassical theory is shown to be in good agreement with quantum
mechanical calculations.

categories: cond-mat.supr-con chao-dyn cond-mat.mes-hall nlin.CD


title:
Anderson impurities in gapless hosts: comparison of renormalization
  group and local moment approaches

abstract:
  The symmetric Anderson impurity model, with a soft-gap hybridization
vanishing at the Fermi level with power law r > 0, is studied via the numerical
renormalization group (NRG). Detailed comparison is made with predictions
arising from the local moment approach (LMA), a recently developed many-body
theory which is found to provide a remarkably successful description of the
problem. Results for the `normal' (r = 0) impurity model are obtained as a
specific case. Particular emphasis is given both to single-particle excitation
dynamics, and to the transition between the strong coupling (SC) and local
moment (LM) phases of the model. Scaling characteristics and asymptotic
behaviour of the SC/LM phase boundaries are considered. Single-particle spectra
are investigated in some detail, for the SC phase in particular. Here, the
modified spectral functions are found to contain a generalized Kondo resonance
that is ubiquitously pinned at the Fermi level; and which exhibits a
characteristic low-energy Kondo scale that narrows progressively upon approach
to the SC->LM transition, where it vanishes. Universal scaling of the spectra
as the transition is approached thus results. The scaling spectrum
characteristic of the normal Anderson model is recovered as a particular case,
and is captured quantitatively by the LMA. In all cases the r-dependent scaling
spectra are found to possess characteristic low-energy asymptotics, but to be
dominated by generalized Doniach-Sunjic tails, in agreement with LMA
predictions.


title:
Density profiles and collective excitations of a trapped two component
  Fermi vapour

abstract:
  We discuss the ground state and the small-amplitude excitations of a
degenerate vapour of fermionic atoms placed in two hyperfine states inside a
spherical harmonic trap. An equations-of-motion approach is set up to discuss
the hydrodynamic dissipation processes from the interactions between the two
components of the fluid beyond mean-field theory and to emphasize analogies
with spin dynamics and spin diffusion in a homogeneous Fermi liquid. The
conditions for the establishment of a collisional regime via scattering against
cold-atom impurities are analyzed. The equilibrium density profiles are then
calculated for a two-component vapour of 40K atoms: they are little modified by
the interactions for presently relevant values of the system parameters, but
spatial separation of the two components will spontaneously arise as the number
of atoms in the trap is increased. The eigenmodes of collective oscillation in
both the total particle number density and the concentration density are
evaluated analytically in the special case of a symmetric two-component vapour
in the collisional regime. The dispersion relation of the surface modes for the
total particle density reduces in this case to that of a one-component Fermi
vapour, whereas the frequencies of all other modes are shifted by the
interactions.


title:
Non-equilibrium, time-dependent effective theory of a weakly coupled
  superconductor at finite temperature

abstract:
  We perform a well defined derivative expansion to obtain the time dependent
effective theory for a BCS superconductor at finite temperature, using an
arbitrary curve in the complex time plane. Our expansion is unique, being free
of any problems related to the order in which analytical continuation and the
derivative expansion are made, or equivalently to the order in which the zero
momentum and zero energy limits are taken. In other words Landau damping terms
are present but do not lead to the pathologies found in standard approaches. We
discuss the reason for this, suggesting that these standard approaches may be
internally inconsistent. The methods presented here are an attempt to overcome
those inconsistencies, and finally, our results are compared to others in the
literature.


title:
Self-similarity under inflation and level statistics: a study in two
  dimensions

abstract:
  Energy level spacing statistics are discussed for a two dimensional
quasiperiodic tiling. The property of self-similarity under inflation is used
to write a recursion relation for the level spacing distributions defined on
square approximants to the perfect quasiperiodic structure.
  New distribution functions are defined and determined by a combination of
numerical and analytical calculations.


title: Global and local level dynamics in chaotic microwave billiards

abstract:
  The spectra of Sinai microwave billiards and rectangular billiards with
statistically distributed circular scatterers have been taken as a function of
the position of one wall, and of one of the scatterers, respectively. Whereas
in the first case the velocity distribution and correlations obey the universal
behaviour predicted by Simons and Altshuler, in the second case a completely
different behaviour is observed. This is due to the fact that a shift of one
wall changes the wave function globally whereas the displacement of one
scatterer only leads to a local perturbance.


title:
Order-out-of-disorder in a gas of elastic quantum strings in 2+1
  dimensions

abstract:
  A limiting case of a dynamical stripe state which is of potential
significance to cuprate superconductors is considered: a gas of elastic quantum
strings in 2+1 dimensions, interacting merely via a hard-core condition. It is
demonstrated that this gas solidifies always, by a mechanism which is the
quantum analogue of the entropic interactions known from soft condensed matter
physics.


title: PrBa_2Cu_3O_{7-y}: Superconducting or Anomalously Magnetic?

abstract:
  In PrBa_2Cu_3O_{7-y} (Pr123) single crystals grown by the flux method the
kink in the magnetic susceptibility chi_{ab}(T), connected with AFM ordering of
Pr, disappears after field cooling (FC) in a field H||ab-plane whereas the kink
in chi_c(T) remains unchanged after FC in H||c-axis. This seems to be connected
with the coupling between the Pr and Cu(2) sublattices. The Curie constant C
determined from the data reported for superconducting Pr123 crystals grown by
traveling-solvent floating zone (TSFZ) method (Zou et al, Phys. Rev. Lett., 80,
1074 (1998)) is about one half of that for our flux crystals. Thus, the
concentration of Pr in TSFZ crystal seems to be about one half of the nominal
for Pr123. Therefore, superconductivity in TSFZ samples is connected most
probably with the partial substitution of Pr by nonmagnetic Ba.


title:
Interaction of Vortices in Complex Vector Field and Stability of a
  ``Vortex Molecule''

abstract:
  We consider interaction of vortices in the vector complex Ginzburg--Landau
equation (CVGLE). In the limit of small field coupling, it is found
analytically that the interaction between well-separated defects in two
different fields is long-range, in contrast to interaction between defects in
the same field which falls off exponentially. In a certain region of parameters
of CVGLE, we find stable rotating bound states of two defects -- a ``vortex
molecule".


title: Evidence for a critical velocity in a Bose-Einstein condensed gas

abstract:
  We have studied dissipation in a Bose--Einstein condensed gas by moving a
blue detuned laser beam through the condensate at different velocities. Strong
heating was observed only above a critical velocity.


title: Magnetic properties of Gd_{1-x}Pr_xBa_2Cu_3O_{7-y} single crystals

abstract:
  Magnetic properties were studied for the high quality Al-free orthorhombic
Gd_{1-x}Pr_xBa_2Cu_3O_{7-y} single crystals (0<=x<=1.0) grown by the flux
method. An indication on the interaction between the Pr and Cu(2) magnetic
sublattices was found for Pr123. Different signs of magnetic anisotropy were
established for the Pr and Gd ions at low temperatures. It was also shown that
superconductivity reported by Zou et al. [Phys. Rev. Lett. 80 (1998) 1074] for
Pr123 single crystals grown by TSZF method seems to be connected with partial
substitution of Ba for the Pr-sites.


title: Superconductivity in a doped Mott insulator

abstract:
  Starting from the d-wave RVB mean-field theory of Kotliar and Liu, we present
a new, long-wavelength/low-energy exact, treatment of gauge fluctuations. The
result is a theory of gapless fermion quasiparticles coupled to superconducting
phase fluctuations. We will discuss the physical implications, and the
similarity/differences with a theory of BCS pairing with phase fluctuations.


title: Fermi Liquid Theory and Ferromagnetic Manganites at Low Temperatures

abstract:
  Fermi liquid characteristics for ferromagnetic ~manganites,
A$_{1-x}$B$_x$MnO$_3$, are evaluated in the tight-binding approximation and
compared with experimental data for the best studied region $x\simeq0.3$. The
bandwidths change only slightly for different compositions. The Sommerfeld
coefficient, $\gamma$, the $T^2$-term in resistivity and main scales in optical
conductivity agree well with the two band model. The ``2.5'' - transition due
to a ``neck'' forming at Fermi surface, is found at $x=0.3$. The mean free path
may change from 3 to 80 interatomic distances in the materials, indicating that
samples' quality remains a pressing issue for the better understanding of
manganites.


title:
Time-dependent four-point density correlation functions in supercooled
  liquids

abstract:
  Dynamical heterogeneity and the decoupling of diffusion and structural
relaxation in a supercooled liquid is investigated in terms of a
time-dependent, fourth-order density correlation function. The generalized
susceptibility $\chi_4(t)$ corresponding to this correlation function has a
maximum at an intermediate time $t_4^*$, and both $t_4^*$ and $\chi_4(t_4^*)$
grow strongly with decreasing temperature. We show that the main contribution
to $\chi_4(t)$ arises from spatial correlations between temporarily localized
(``caged'') particles. We compare $\chi_4(t)$ with a generalized susceptibility
$\chi_M(t)$ related to a correlation function of squared particle
displacements, and show that while $t_4^*$ is roughly proportional to the
$\alpha$-relaxation time, $t_M^*$ is proportional to the inverse of the
self-diffusion coefficient.


title:
From Massively Parallel Algorithms and Fluctuating Time Horizons to
  Non-equilibrium Surface Growth

abstract:
  We study the asymptotic scaling properties of a massively parallel algorithm
for discrete-event simulations where the discrete events are Poisson arrivals.
The evolution of the simulated time horizon is analogous to a non-equilibrium
surface. Monte Carlo simulations and a coarse-grained approximation indicate
that the macroscopic landscape in the steady state is governed by the
Edwards-Wilkinson Hamiltonian. Since the efficiency of the algorithm
corresponds to the density of local minima in the associated surface, our
results imply that the algorithm is asymptotically scalable.


title: Quantum Antidots: Coulomb Blockade or no Coulomb Blockade?

abstract: Comment on M. Kataoka et al., Phys. Rev. Lett. 83, 160 (1999).


title:
Probing Ion-Ion and Electron-Ion Correlations in Liquid Metals within
  the Quantum Hypernetted Chain Approximation

abstract:
  We use the Quantum Hypernetted Chain Approximation (QHNC) to calculate the
ion-ion and electron-ion correlations for liquid metallic Li, Be, Na, Mg, Al,
K, Ca, and Ga. We discuss trends in electron-ion structure factors and radial
distribution functions, and also calculate the free-atom and metallic-atom
form-factors, focusing on how bonding effects affect the interpretation of
X-ray scattering experiments, especially experimental measurements of the
ion-ion structure factor in the liquid metallic phase.


title: Block bond-order potential as a convergent moments-based method

abstract:
  The theory of a novel bond-order potential, which is based on the block
Lanczos algorithm, is presented within an orthogonal tight-binding
representation. The block scheme handles automatically the very different
character of sigma and pi bonds by introducing block elements, which produces
rapid convergence of the energies and forces within insulators, semiconductors,
metals, and molecules. The method gives the first convergent results for
vacancies in semiconductors using a moments-based method with a low number of
moments. Our use of the Lanczos basis simplifies the calculations of the band
energy and forces, which allows the application of the method to the molecular
dynamics simulations of large systems. As an illustration of this convergent
O(N) method we apply the block bond-order potential to the large scale
simulation of the deformation of a carbon nanotube.


title:
Magnetoconductance Oscillations in Ballistic
  Semiconductor-Superconductor Junctions

abstract:
  The mechanism of the magnetoconductance oscillations in junctions of a
ballistic semiconductor and a superconductor is discussed. The oscillations
appear when both the normal and the Andreev reflection occur at the interface.
The interplay between the classical cyclotron motion of a quasiparticle and the
phase shift caused by the magnetic field is the origin of the conductance
oscillations.


title:
Spin-fluctuation exchange study of superconductivity in two- and
  three-dimensional single-band Hubbard models

abstract:
  In order to identify the most favorable situation for superconductivity in
the repulsive single-band Hubbard model, we have studied instabilities for
d-wave pairing mediated by antiferromagnetic spin fluctuations and p-pairing
mediated by ferromagnetic fluctuations with the fluctuation exchange
approximation in both two dimensions and three dimensions. By systematically
varying the band filling and band structure we have shown that (i) d-pairing is
stronger in two dimensions than in three dimensions, and (ii) p-pairing is much
weaker than the d-pairing.


title:
Application of the lattice Green's function for calculating the
  resistance of an infinite networks of resistors

abstract:
  We calculate the resistance between two arbitrary grid points of several
infinite lattice structures of resistors by using lattice Green's functions.
The resistance for $d$ dimensional hypercubic, rectangular, triangular and
honeycomb lattices of resistors is discussed in detail. We give recurrence
formulas for the resistance between arbitrary lattice points of the square
lattice. For large separation between nodes we calculate the asymptotic form of
the resistance for a square lattice and the finite limiting value of the
resistance for a simple cubic lattice. We point out the relation between the
resistance of the lattice and the van Hove singularity of the tight-binding
Hamiltonian. Our Green's function method can be applied in a straightforward
manner to other types of lattice structures and can be useful didactically for
introducing many concepts used in condensed matter physics.


title:
Effective and Asymptotic Critical Exponents of Weakly Diluted Quenched
  Ising Model: 3d Approach Versus $\epsilon^{1/2}$-Expansion

abstract:
  We present a field-theoretical treatment of the critical behavior of
three-dimensional weakly diluted quenched Ising model. To this end we analyse
in a replica limit n=0 5-loop renormalization group functions of the
$\phi^4$-theory with O(n)-symmetric and cubic interactions (H.Kleinert and
V.Schulte-Frohlinde, Phys.Lett. B342, 284 (1995)). The minimal subtraction
scheme allows to develop either the $\epsilon^{1/2}$-expansion series or to
proceed in the 3d approach, performing expansions in terms of renormalized
couplings. Doing so, we compare both perturbation approaches and discuss their
convergence and possible Borel summability. To study the crossover effect we
calculate the effective critical exponents providing a local measure for the
degree of singularity of different physical quantities in the critical region.
We report resummed numerical values for the effective and asymptotic critical
exponents. Obtained within the 3d approach results agree pretty well with
recent Monte Carlo simulations. $\epsilon^{1/2}$-expansion does not allow
reliable estimates for d=3.


title:
Non-Gaussian distribution of nearest-neighbour Coulomb peak spacings in
  metallic single electron transistors

abstract:
  The distribution of nearest-neighbour spacings of Coulomb blockade
oscillation peaks in normal conducting aluminum single electron transistors is
found to be non-Gaussian. A pronounced tail to reduced spacings is observed,
which we attribute to impurity-specific parametric charge rearrangements close
to the transistor. Our observation may explain the absence of a Wigner-Dyson
distribution in the experimental nearest-neighbour spacing distributions in
semiconductor quantum dots.


title: Non-equilibrium dynamics in an interacting nanoparticle system

abstract:
  Non-equilibrium dynamics in an interacting Fe-C nanoparticle sample,
exhibiting a low temperature spin glass like phase, has been studied by low
frequency ac-susceptibility and magnetic relaxation experiments. The
non-equilibrium behavior shows characteristic spin glass features, but some
qualitative differences exist. The nature of these differences is discussed.


title:
Interplay of Fulde-Ferrell-Larkin-Ovchinnikov and Vortex states in
  two-dimensional Superconductors

abstract:
  Clean superconductors with weakly coupled conducting planes have been
suggested as promising candidates for observing the
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. We consider here a layered
superconductor in a magnetic field of arbitrary orientation with respect to the
conducting plane. In this case there is competition of spin-pair-breaking and
orbital-pair-breaking effects. In previous work, phase boundaries characterized
by Landau quantum numbers n > 0 have been predicted. Here, we calculate the
actual structure of the stable states below Hc2 by minimizing the free energy.
We find several new order parameter structures differing from both the
traditional Abrikosov and FFLO solutions. Some interesting unsolved questions
appear in the limit of large n.


title: Field emission properties of nano-composite carbon nitride films

abstract:
  A modified cathodic arc technique has been used to deposit carbon nitride
thin films directly on n+ Si substrates. Transmission Electron Microscopy
showed that clusters of fullerene-like nanoparticles are embedded in the
deposited material. Field emission in vacuum from as-grown films starts at an
electric field strength of 3.8 V/micron. When the films were etched in an
HF:NH4F solution for ten minutes, the threshold field decreased to 2.6
V/micron. The role of the carbon nanoparticles in the field emission process
and the influence of the chemical etching treatment are discussed.


title: Time-Dependent Transport in Mesoscopic Structures

abstract:
  A discussion of recent work on time-dependent transport in mesoscopic
structures is presented. The discussion emphasizes the use of time-dependent
transport to gain information on the charge distribution and its collective
dynamics. We discuss the RC-time of mesoscopic capacitors, the dynamic
conductance of quantum point contacts and dynamic weak localization effects in
chaotic cavities. We review work on adiabatic quantum pumping and
photon-assisted transport, and conclude with a list which demonstrates the wide
range of problems which are of interest.


title:
Symmetry of the Atomic Electron Density in Hartree, Hartree-Fock, and
  Density Functional Theory

abstract:
  The density of an atom in a state of well-defined angular momentum has a
specific finite spherical harmonic content, without and with interactions.
Approximate single-particle schemes, such as the Hartree, Hartree-Fock, and
Local Density Approximations, generally violate this feature. We analyze, by
means of perturbation theory, the degree of this violation and show that it is
small. The correct symmetry of the density can be assured by a
constrained-search formulation without significantly altering the calculated
energies. We compare our procedure to the (different) common practice of
spherically averaging the self-consistent potential. Kohn-Sham density
functional theory with the exact exchange-correlation potential has the correct
finite spherical harmonic content in its density; but the corresponding exact
single particle potential and wavefunctions contain an infinite number of
spherical harmonics.


title: Metallic stripe in two dimensions: stability and spin-charge separation

abstract:
  The problems of charge stripe formation, spin-charge separation, and
stability of the antiphase domain wall (ADW) associated with a stripe are
addressed using an analytical approach to the t-J_z model. We show that a
metallic stripe together with its ADW is the ground state of the problem in the
low doping regime. The stripe is described as a system of spinons and
magnetically confined holons strongly coupled to the two dimensional (2D) spin
environment with holon-spin-polaron elementary excitations filling a
one-dimensional band.


title:
Symmetry, Geometry, Topology and Spin: Heisenberg spins in the continuum
  limit/magnetic vesicles

abstract:
  In this thesis I present my research on the exotic configurations of
antiferromagnetic systems characterised by a topological invariant. The
research presented outlines the construction of novel local antiferromagnetic
degrees of freedom for low dimensional antiferromagnetic lattices. This new
construction reproduces the real division algebra hierarchy satisfied by the
nonlinear sigma-model and reveals the presence of a novel local gauge field. I
have also studied elastic magnetic vesicles of spherical and toric genus in the
presence of a magnetic soliton. My studies reveal a global shrinking, with
local swellings in the regions where the soliton presents a spin-flip. The
geometrical origin of this novel phenomena led me to interpret the geometric
frustration of magnetic vesicles as the competition between the two topological
orders present. The microscopic mechanism and topological competition suggested
above go beyond the scope of this thesis, providing a microscopic explanation
for the Fermi-Bose transmutation and a way to deal with this type of exotic
physics.


title: New Algebraic Formulation of Density Functional Calculation

abstract:
  This article addresses a fundamental problem faced by the ab initio
community: the lack of an effective formalism for the rapid exploration and
exchange of new methods. To rectify this, we introduce a novel, basis-set
independent, matrix-based formulation of generalized density functional
theories which reduces the development, implementation, and dissemination of
new ab initio techniques to the derivation and transcription of a few lines of
algebra. This new framework enables us to concisely demystify the inner
workings of fully functional, highly efficient modern ab initio codes and to
give complete instructions for the construction of such for calculations
employing arbitrary basis sets. Within this framework, we also discuss in full
detail a variety of leading-edge ab initio techniques, minimization algorithms,
and highly efficient computational kernels for use with scalar as well as
shared and distributed-memory supercomputer architectures.


title:
Patterns of consumption in socio-economic models with heterogeneous
  interacting agents

abstract:
  We study consumption behaviour in systems with heterogeneous interacting
agents. Two different models are introduced, respectively with long and short
range interactions among agents. At any time step an agent decides whether or
not to consume a good, doing so if this provides positive utility. Utility is
affected by idiosyncratic preferences and costs as well as externalities from
other agents. Agents are ranked in classes and recognize peer, distinction and
aspiration groups. We simulate the system for different choices of the
parameters and identify different complex patterns: a steady state regime with
a variety of consumption modes of behaviour, and a wave/cycle regime. The cases
of fad and value goods are both analyzed.


title: Reduced Density Matrix Approach to Phononic Dissipation in Friction

abstract:
  Understanding mechanisms for energy dissipation from nanoparticles in contact
with large samples is a central problem in describing friction microscopically.
Calculation of the reduced density matrix appears to be the most suitable metho
to study such systems that are coupled to a large environment. In this paper
the time evolution of the reduced density matrix has been evaluated for an
arbitrary system coupled to a heat reservoir. The formalism is then applied to
study the vibrational relaxation following the stick-slip motion of a small
adsorbate on a surface. The frequency dependence of the relaxation time is also
determined.


title: Mesoscopic fluctuations of the Coulomb drag

abstract:
  We consider mesoscopic fluctuations of the Coulomb drag coefficient $\rho_D$
in the system of two separated two-dimensional electron gases. It is shown that
at low temperatures sample to sample fluctuations of $\rho_D$ exceed its
ensemble average. It means that in such a regime the sign of $\rho_D$ is random
and the temperature dependence almost saturates $\rho_D \sim 1/\sqrt{T}$.


title:
Superexchange via Cluster States: Calculations of Spin-Phonon Coupling
  Constants for CuGeO3

abstract:
  Calculations for spin-phonon coupling constants in CuGeO3 are presented,
applying fourth order superexchange perturbation theory to an extended Hubbard
model. In our treatment, the intermediate oxygen ligand states are described by
band-like cluster states, due to the presence of significant O(p)-O(p) hopping.
We also include the effect of the Ge ions on the O ligand states.
  We find a considerable q-dependence of the spin-phonon coupling. For the
pi-modes involved in the spin-Peierls transition, our results of the coupling
constants are in fair agreement with the work of Werner, Gros, and Braden. Yet
some discrepancies remain, especially concerning the coupling to the
vibrations, which modulate the O(2)-O(2)-Ge angle delta. Our studies of the
pressure dependence of the magnetic coupling constants J_1 and J_2 suggest,
that relatively large non-linear effects are present, even at small pressure
values, probably due to the existence of a `soft', van-der-Waals-type bond
direction in CuGeO3.


title: Orbital current mode in elliptical quantum dots

abstract:
  An orbital current mode peculiar to deformed quantum dots is theoretically
investigated; first by using a simple model that allows to interpret
analytically its main characteristics, and second, by numerically solving the
microscopic equations of time evolution after an initial perturbation within
the time-dependent local-spin-density approximation. Results for different
deformations and sizes are shown.


title:
Micromagnetic simulations of thermally activated magnetization reversal
  of nanoscale magnets

abstract:
  Numerical integration of a stochastic Landau-Lifshitz-Gilbert equation is
used to study dynamic processes in single-domain nanoscale magnets at nonzero
temperatures. Special attention is given to including thermal fluctuations as a
Langevin term, and the Fast Multipole Method is used to calculate dipole-dipole
interactions. It is feasible to simulate these dynamics on the nanosecond time
scale for spatial discretizations that involve on the order of 10000 nodes
using a desktop workstation. The nanoscale magnets considered here are single
pillars with large aspect ratio. Hysteresis-loop simulations are employed to
study the stable and metastable configurations of the magnetization. Each
pillar has magnetic end caps. In a time-dependent field the magnetization of
the pillars is observed to reverse via nucleation, propagation, and coalescence
of the end caps. In particular, the end caps propagate into the magnet and meet
near the middle. A relatively long-lived defect is formed when end caps with
opposite vorticity meet. Fluctuations are more important in the reversal of the
magnetization for fields weaker than the zero-temperature coercive field, where
the reversal is thermally activated. In this case, the process must be
described by its statistical properties, such as the distribution of switching
times, averaged over a large number of independent thermal histories.


title: Non-equilibrium Thermodynamics and Hydrodynamic Fluctuations

abstract:
  The reformulation of nonequilibirum thermodynamics, to include the treatment
of thermodynamic fluctuations, is applied to the hydrodynamic fluctuations of a
simple fluid. It is shown that the nonequilibrium thermodynamic scheme leads to
the explicit form of the Fokker-Planck equation which describes the time
behaviour of the probability distribution function of these hydrodynamic
fluctuations as well as the irreversible processes which are connected with
this behaviour.


title: Experimental Evidence for Resonant-Tunneling in a Luttinger-Liquid

abstract:
  We have measured the low temperature conductance of a one-dimensional island
embedded in a single mode quantum wire. The quantum wire is fabricated using
the cleaved edge overgrowth technique and the tunneling is through a single
state of the island. Our results show that while the resonance line shape fits
the derivative of the Fermi function the intrinsic line width decreases in a
power law fashion as the temperature is reduced. This behavior agrees
quantitatively with Furusaki's model for resonant tunneling in a
Luttinger-liquid.


title:
Decoherence effects on the generation of exciton entangled states in
  coupled quantum dots

abstract:
  We report on exciton-acoustic-phonon coupling effects on the generation of
exciton maximally entangled states in N=2 and 3 quantum dot systems. In
particular, we address the question of the combined effect of laser pulses,
appropriate for generating Bell and Greenberger-Horne-Zeilinger entangled
states, together with decoherence mechanisms as provided by a phonon reservoir.
By solving numerically the master equation for the optically driven
exciton-phonon kinetics, we show that the generation of maximally entangled
exciton states is preserved over a reasonable parameter window.


title: Unscreened Coulomb repulsion in the one dimensional electron gas

abstract:
  A tight binding model of electrons interacting via bare Coulomb repulsion is
numerically investigated by use of the Density Matrix Renormalization Group
method which we prove applicable also to very long range potentials. From the
analysis of the elementary excitations, of the spin and charge correlation
functions and of the momentum distribution, a picture consistent with the
formation of a one dimensional "Wigner crystal" emerges, in quantitative
agreement with a previous bosonization study. At finite doping, Umklapp
scattering is shown to be ineffective in the presence of long range forces.


title:
The Design of Random Surfaces with Specified Scattering Properties:
  Surfaces that Suppress Leakage

abstract:
  We present a method for generating a one-dimensional random metal surface of
finite length L that suppresses leakage, i.e. the roughness-induced conversion
of a surface plasmon polariton propagating on it into volume electromagnetic
waves in the vacuum above the surface. Perturbative and numerical simulation
calculations carried out for surfaces generated in this way show that they
indeed suppress leakage.


title:
Application of the Projected Dynamics Method to an Anisotropic
  Heisenberg Model

abstract:
  The Projected Dynamics method was originally developed to study metastable
decay in ferromagnetic discrete spin models. Here, we apply it to a classical,
continuous Heisenberg model with anisotropic ferromagnetic interactions, which
evolves under a Monte Carlo dynamic. The anisotropy is sufficiently large to
allow comparison with the Ising model. We describe the Projected Dynamics
method and how to apply it to this continuous-spin system. We also discuss how
to extract metastable lifetimes and how to extrapolate from small systems to
larger systems.


title:
gl(N|N) Super-Current Algebras for Disordered Dirac Fermions in Two
  Dimensions

abstract:
  We consider the non-hermitian 2D Dirac Hamiltonian with (A): real random
mass, imaginary scalar potential and imaginary gauge field potentials, and (B)
arbitrary complex random potentials of all three kinds. In both cases this
Hamiltonian gives rise to a delocalization transition at zero energy with
particle-hole symmetry in every realization of disorder. Case (A) is in
addition time-reversal invariant, and can also be interpreted as the
random-field XY Statistical Mechanics model in two dimensions. The
supersymmetric approach to disorder averaging results in current-current
perturbations of $gl(N|N)$ super-current algebras. Special properties of the
$gl(N|N)$ algebra allow the exact computation of the beta-functions, and of the
correlation functions of all currents. One of them is the Edwards-Anderson
order parameter. The theory is `nearly conformal' and possesses a
scale-invariant subsector which is not a current algebra. For N=1, in addition,
we obtain an exact solution of all correlation functions. We also study the
delocalization transition of case (B), with broken time reversal symmetry, in
the Gade-Wegner (Random-Flux) universality class, using a GL(N|N;C)/U(N|N)
sigma model, as well as its PSL(N|N) variant, and a corresponding generalized
random XY model. For N=1 the sigma model is shown to be identical to the
current-current perturbation. For the delocalization transitions (case (A) and
(B)) a density of states, diverging at zero energy, is found.

categories: cond-mat.mes-hall cond-mat.dis-nn cond-mat.stat-mech hep-th


title: A simple semiclassical approach to Kramers' problem

abstract:
  We show that Wigner-Leggett-Caldeira equation for Wigner phase space
distribution function which describes the quantum Brownian motion of a particle
in a force field in a high temerature, Ohmic environment can be identified as a
semiclassical version of Kramers' equation. Based on an expansion in powers of
$\hbar$ we solve this equation to calculate the semiclassical correction to
Kramers' rate.


title:
Magnetic Properties of disordered CoCu alloys:A first principles
  approach

abstract:
  Crystalline Co$_{x}$Cu$_{1-x}$ alloys show interesting magnetic behavior over
the entire concentration regime. We here present a fully self- consistent first
principles electronic structure studies of the electronic structure and
magnetic properties of the system.We present results for the variation of
density of states, magnetic moment,spin susceptibility and Curie temperature.


title: Time Evolution of Spin Waves

abstract:
  A rigorous derivation of macroscopic spin-wave equations is demonstrated. We
introduce a macroscopic mean-field limit and derive the so-called
Landau-Lifshitz equations for spin waves. We first discuss the ferromagnetic
Heisenberg model at T=0 and finally extend our analysis to general spin
hamiltonians for the same class of ferromagnetic ground states.

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


title:
Photoinduced IR absorption in (La(1-x)Sr(x)Mn)(1-\delta)O3: changes of
  the anti-Jahn-Teller polaron binding energy with doping

abstract:
  Photoinduced IR absorption was measured in (La(1-x)Sr(x)Mn)(1-\delta)O3. A
midinfrared peak centered at ~ 5000 cm$^{-1}$ was observed in the x=0
antiferromagnetic sample. The peak diminishes and softens as hole doping is
increased. The origin of the photoinduced absorption peak is atributted to the
photon assisted hopping of anti-Jahn-Teller polarons formed by photoexcited
charge carriers, whose binding energy decreases with increasing hole doping.
The shape of the peak indicates that the polarons are small.


title: Capillary-gravity waves: The effect of viscosity on the wave resistance

abstract:
  The effect of viscosity on the wave resistance experienced by a 2d
perturbation moving at uniform velocity over the free surface of a fluid is
investigated. The analysis is based on Rayleigh's linearized theory of
capillary-gravity waves. It is shown in particular that the wave resistance
remains bounded as the velocity of the perturbation approches the minimun phase
speed, unlike what is predicted by the inviscid theory.


title: Universality classes for the "ricepile" model with absorbing properties

abstract:
  The absorbing "ricepile" model with stochastic toppling rules has been
numerically studied. Local limited, local unlimited, nonlocal limited and
nonlocal unlimited versions of the absorbing model have been investigated.
Transport properties and different dynamical regimes of all of the models have
been analysed, from the point of view of self organized criticality (SOC).
Phase transitions between different dynamical regimes were studied in detail.
It was shown, that the absorbing models belong to two different universality
classes.


title:
Kinetic energy of a trapped Fermi gas interacting with a Bose-Einstein
  condensate

abstract:
  We study a confined mixture of bosons and fermions in the regime of quantal
degeneracy, with particular attention to the effects of the interactions on the
kinetic energy of the fermionic component. We are able to explore a wide region
of system parameters by identifying two scaling variables which completely
determine its state at low temperature. These are the ratio of the
boson-fermion and boson-boson interaction strengths and the ratio of the radii
of the two clouds. We find that the effect of the interactions can be sizeable
for reasonable choices of the parameters and that its experimental study can be
used to infer the sign of the boson-fermion scattering length. The interplay
between interactions and thermal effects in the fermionic kinetic energy is
also discussed.


title:
Near-field induced FIR Josephson-detection by c-axis-oriented
  YBa_2Cu_3O_7-delta-films

abstract:
  A novel approach to intrinsic Josephson-detection of far infrared radiation
is reported utilizing near-zone field effects at electric contacts on c-axis
oriented YBa_2Cu_3O_7-delta films. While only a bolometric signal was observed
focusing the radiation far off the contacts on c-axis normal films, irradiating
the edge of contacts yielded an almost wavelength independent fast signal
showing the characteristic intensity dependence of Josephson-detection. The
signal is attributed to a c-axis parallel component of the electric radiation
field being generated in the near-zone field of diffraction at the metallic
contact structures.


title: Effective Field Theory of the Random Flux Model

abstract:
  The random flux model (defined here as a model of lattice fermions hopping
under the influence of maximally random link disorder) is analysed field
theoretically. It is shown that the long range physics of the model is
described by the supersymmetric version of a field theory that has been derived
earlier in connection with lattice fermions subject to weak random hopping.
More precisely, the field theory relevant for the behaviour of n-point
correlation functions is of non-linear sigma model type, where the group
GL(n|n) is the global invariant manifold. It is argued that the model
universally describes the long range physics of random phase fermions and
provides further evidence in favour of the existence of delocalised states in
the middle of the band in two dimensions. The same formalism is applied to the
study of non-Abelian generalisations of the random flux model, i.e. N-component
fermions whose hopping is mediated by random U(N) matrices. We discuss some
physical applications of these models and argue that, for sufficiently large N,
the existence of long range correlations in the band center (equivalent to
metallic behaviour in the Abelian case) can be safely deduced from the RG
analysis of the model.


title:
A corresponding states approach to Small-Angle-Scattering for
  polydisperse ionic colloidal fluids

abstract:
  Approximate scattering functions for polydisperse ionic colloidal fluids are
obtained by a corresponding states approach. This assumes that all pair
correlation functions $g_{\alpha \beta}(r)$ of a polydisperse fluid are
conformal to those of an appropriate monodisperse binary fluid (reference
system) and can be generated from them by scaling transformations. The
correspondence law extends to ionic fluids a {\it scaling approximation} (SA)
successfully proposed for nonionic colloids in a recent paper. For the
primitive model of charged hard spheres in a continuum solvent, the partial
structure factors of the monodisperse binary reference system are evaluated by
solving the Orstein-Zernike (OZ) integral equations coupled with an approximate
closure. The SA is first tested within the mean spherical approximation (MSA)
closure, which allows analytical solutions. The results are found in good
overall agreement with exact MSA predictions up to relevant polidispersity. The
SA is shown to be an improvement over the ``decoupling approximation'' extended
to the ionic case. The simplicity of the SA scheme allows its application also
when the OZ equations can be solved only numerically. An example is then given
by using the hypernetted chain (HNC) closure. Shortcomings of the SA approach,
its possible use in the analysis of experimental scattering data and other
related points are also briefly addressed.


title:
Hopping motion of lattice gases through nonsymmetric potentials under
  strong bias conditions

abstract:
  The hopping motion of lattice gases through potentials without
mirror-reflection symmetry is investigated under various bias conditions. The
model of 2 particles on a ring with 4 sites is solved explicitly; the resulting
current in a sawtooth potential is discussed. The current of lattice gases in
extended systems consisting of periodic repetitions of segments with sawtooth
potentials is studied for different concentrations and values of the bias.
Rectification effects are observed, similar to the single-particle case. A
mean-field approximation for the current in the case of strong bias acting
against the highest barriers in the system is made and compared with numerical
simulations. The particle-vacancy symmetry of the model is discussed.


title: Single parameter scaling in one-dimensional localization revisited

abstract:
  The variance of the Lyapunov exponent is calculated exactly in the
one-dimensional Anderson model with random site energies distributed according
to the Cauchy distribution. We find a new significant scaling parameter in the
system, and derive an exact analytical criterion for single parameter scaling
which differs from the commonly used condition of phase randomization. The
results obtained are applied to the Kronig-Penney model with the potential in
the form of periodically positioned $\delta$-functions with random strength.


title: Low Dimensional Correlated Systems: Cugeo_3 and Nav_2O_5

abstract:
  Some of the properties of the low-dimensional electronically correlated
materials \cgo and \nvo are discussed. The emphasis lies on recent results
obtained using Raman scattering and optical absorption spectroscopy as a
function of temperature, magnetic field and hydrostatic pressure.


title:
Thermodynamic identities and particle number fluctuations in weakly
  interacting Bose--Einstein condensates

abstract:
  We derive exact thermodynamic identities relating the average number of
condensed atoms and the root-mean-square fluctuations determined in different
statistical ensembles for the weakly interacting Bose gas confined in a box.
This is achieved by introducing the concept of {\it auxiliary partition
functions} for model Hamiltonians that do conserve the total number of
particles. Exploiting such thermodynamic identities, we provide the first,
completely analytical prediction of the microcanonical particle number
fluctuations in the weakly interacting Bose gas. Such fluctuations, as a
function of the volume V of the box are found to behave normally, at variance
with the anomalous scaling behavior V^{4/3} of the fluctuations in the ideal
Bose gas.


title:
Advanced Dynamic Algorithms for the Decay of Metastable Phases in
  Discrete Spin Models: Bridging Disparate Time Scales

abstract:
  An overview of advanced dynamical algorithms capable of spanning the widely
disparate time scales that govern the decay of metastable phases in discrete
spin models is presented. The algorithms discussed include constrained
transfer-matrix, Monte Carlo with Absorbing Markov Chains (MCAMC), and
projective dynamics (PD) methods. The strengths and weaknesses of each of these
algorithms are discussed, with particular emphasis on identifying the parameter
regimes (system size, temperature, and field) in which each algorithm works
best.