title:
Theory of solitons, polarons and multipolarons in one dimension: An
  alternative formulation

abstract:
  We develop an alternative formulation of the theory of solitons, polarons and
multipolarons in quasi-one-dimensional degenerate and non-degenerate conducting
polymers, starting from the continuum Hamiltonian introduced by Brazovskii and
Kirova. Based on a convenient real-space representation of the electron Green
function in one dimension, we present a simple method of calculating the Green
function and the density of states in the presence of a single soliton or
polaron defect, using which we derive exact expressions for the soliton,
polaron and multipolaron excitation energies and the self-consistent gap
functions for an arbitrary value of the electron-phonon coupling constant. We
apply our results to $cis$-polyacetylene.


title:
Binding Energy of Impurity in a Size Quantized Coated Semiconductor
  Wire: Role of the Dielectric-Constant Mismatch

abstract:
  Within the framework of staircase infinitely deep (SIW) potential well model
the effect of dielectric constant mismatch between the size-quantized
semiconducting wire, coating and surrounding environment on impurity binding
energy is considered. Calculations are done in both the absence and presence of
magnetic field applied along the wire axis. By the variation method the
dependences of binding energy of hydrogen-like impurity located on the wire
axis on the alloy concentration, effective mass ratio, dielectric constant
mismatch and magnetic field are found for the GaAs-Ga_{1-x}Al_{x}AS system.


title: Metastabilities in vortex matter

abstract:
  We extend the classical theory for supercooling across first order phase
transitions to the case when both density and temperature are control
variables. The observable region of metastability then depends on the path
followed in this space of two variables. Since the density of vortex matter in
superconductors can be easily varied over a wide range by varying applied
field, it is ideal for experimental tests. We found, in our studies on the
`peak effect' in the mixed state of superconducting CeRu$_2$, supercooled
states whose observable region of metastability depends on the path followed in
(H,T) space, consistent with our predictions. We also discuss phenomena in hard
superconductors that are well understood within Bean's critical state model. We
conclude that the path dependence of metastablity associated with hindered
kinetics may be opposite to that predicted for metastability associated with
supercooling across a first order transition.


title:
Non-linear phenomena in electrical circuits: Simulation of non-linear
  relativistic field theory and possible applications

abstract:
  We propose the non-accelerator non-low-temperature simulator of quantum-field
effects which is based on the feeder circuits with the special feedback. By
means of it one can study the field models which contain fundamental concepts
in the modern field theory but do not exist in nature in a separate form.
Besides, several field phenomena might find technological applications by
virtue of the electrical analogy.

categories: cond-mat.mtrl-sci cond-mat.mes-hall hep-ph hep-th


title: Critical Behavior of Heisenberg Chains Coupled to Phonons

abstract: This paper has been withdrawn by the author due to unspecified problems.


title: Exact solution of a Z(4) gauge Potts model on planar lattices

abstract:
  The exact solution of a general Z(4) gauge Potts model with a single and
double plaquette representation of the action is found on a subspace of
gauge-coupling parameters on the square and triangular lattices. The two
Ising-type critical lines of a second-order phase transition for the model on a
square lattice are found. For the model on a triangular lattice the two
critical surfaces of an Ising-type and two nontrivial lines of a second-order
phase transition with different critical behavior than on the critical surfaces
are found. It is shown that a two dimensional (2D) general Z(4) gauge Potts
model with single and double plaquette representation of the action and a 2D
spin-3/2 Ising model belong to the same universality class.


title: Broad Histogram Method for Multiparametric Hamiltonians

abstract:
  We extended the Broad Histogram Method in order to obtain spectral
degeneracies for systems with multiparametric Hamiltonians. As examples we
obtained the critical lines for the square lattice Ising model with nearest and
next-nearest neighbor interactions and the antiferromagnetic Ising model in an
external field. For each system, the entire critical line is obtained using
data from a single computer run. We also discuss the accuracy and efficiency of
our method.


title: Simulations of liquid crystal hydrodynamics

abstract:
  We present a lattice Boltzmann algorithm for liquid crystal hydrodynamics.
The coupling between the tensor order parameter and the flow is treated
consistently allowing investigation of a wide range of non-Newtonian flow
behavior. We present results for the effect of hydrodynamics on defect
coalescence; of the appearance of the log-rolling and kayaking states in
Poiseuille flow; and for banding and coexistence of isotropic and nematic
phases under shear.


title:
Ab initio study of magnetic structure and chemical reactivity of Cr2O3
  and its (0001) surface

abstract:
  We present the first ab initio density functional theory study of the
oxygen-terminated Cr2O3 (0001) surface within the local spin-density
approximation (LSDA). We find that spin plays a critical role for even the most
basic properties of Cr2O3 such as the structure and mechanical response of the
bulk material. The surface exhibits strong relaxations and changes in
electronic and magnetic structure with important implications for the chemical
reactivity and unusual spin-dependent catalytic activity of the surface. Unlike
the bulk, the outermost chromium bilayer is ferromagnetically ordered, and the
surface oxygen layer exhibits appreciable net spin polarization in the opposite
sense. Surprisingly, despite this ferrimagnetic order, the chemically important
states near the Fermi level exhibit ferromagnetic order and thus favor
electronic spin alignment of species interacting with the surface. Finally, we
also find a high density of unoccupied electronic surface states available to
participate in the chemical reactivity of the surface.


title: Scanning Gate Spectroscopy on Nanoclusters

abstract:
  A gated probe for scanning tunnelling microscopy (STM) has been developed.
The probe extends normal STM operations by means of an additional electrode
fabricated next to the tunnelling tip. The extra electrode does not make
contact with the sample and can be used as a gate. We report on the recipe used
for fabricating the tunnelling tip and the gate electrode on a silicon nitride
cantilever. We demonstrate the functioning of the scanning gate probes by
performing single-electron tunnelling spectroscopy on 20-nm gold clusters for
different gate voltages.


title: On the response of composite fermions to weak electrostatic potentials

abstract:
  We establish that the response to static perturbations of two-dimensional
electron systems (2DESs), exposed to magnetic field B, in states with the
Landau-level filling fractions \nu close to one such as 1/2, is singularly
different from that of 2DESs at small |B|. Thus in addition to demonstrating
the sever inadequacy of the treatment of composite fermions as non-interacting
particles, we show, in contradiction to a recent theoretical finding, that the
physical origin of the observed behaviour of the dc longitudinal
magneto-resistivity for \nu close to 1/2 in periodically modulated 2DESs
remains to be determined.


title: Dynamic instabilities and memory effects in vortex matter

abstract:
  Recent studies have shown a number of surprising vortex dynamics phenomena
both in low and high temperature superconductors, which include: low frequency
noise, slow voltage oscillations, history dependent dynamic response, memory of
the direction, amplitude, duration, and frequency of the previously applied
current, suppression of a large ac vortex response by a very small dc bias, and
a strong frequency dependence. Taken together, these phenomena are incompatible
with the current understanding of bulk vortex dynamics. We propose a generic
mechanism to account for these observations in terms of the competition between
the injection of a disordered vortex phase through the surface barriers at the
sample edges, and the annealing of this metastable disorder by the transport
current. The model is confirmed by investigating the current distribution
across NbSe2 single crystals using arrays of Hall sensors. For an ac current
only narrow regions near the edges are in the pinned disordered phase resulting
in a large response. In the presence of a dc bias a wide region of the sample
is filled by the disordered phase preventing vortex motion. The resulting
spatial variation of the disorder across the sample acts as an active memory of
the previously applied current sequence.


title:
Effect of Order-Parameter Suppression on Scattering by Isolated
  Impurities in Asymmetric Bands

abstract:
  The single-impurity problem in d-wave superconductors with asymmetric bands
is discussed. The effect of local order parameter suppression near the impurity
is to shift the quasiparticle resonance. Contrary to previous work [A. Shnirman
et al., Phys. Rev. B 60, 7517 (1999)] we find that the direction of the shift
is not universally towards the strong scattering limit.


title: Upper critical dimension in the scaling theory of localization

abstract:
  It is argued that the Thouless number g(L) is not the only parameter relevant
in scale transformations, and that the second parameter connected with
off-diagonal disorder should be introduced. A two-parameter scaling theory is
suggested that explains a phenomenon of the upper critical dimension from the
viewpoint of scaling ideas.


title:
Magnetization Measurements on Single Crystals of Superconducting
  Ba0.6K0.4BiO3

abstract:
  Extensive measurements of the magnetization of superconducting single crystal
samples of Ba0.6K0.4BiO3} have been made using SQUID and cantilever force
magnetometry at temperatures ranging between 1.3 and 350 K and in magnetic
fields from near zero to 27 T. Hysteresis curves of magnetization versus field
allow a determination of the thermodynamic critical field, the reversibility
field, and the upper critical field as a function of temperature. The lower
critical field is measured seperately and the Ginzburg-Landau parameter is
found to be temperature dependent. All critical fields have higher T = 0 limits
than have been previously noted and none of the temperature dependence of the
critical fields follow the expected power laws leading to possible alternate
interpretation of the thermodynamic nature of the superconducting transition.


title:
Interrelation of Superconducting and Antiferromagnetic Gaps in High-Tc
  Compounds: a Test Case for the SO(5) Theory

abstract:
  Recent angle resolved photoemission data, which found evidence for a
d-wave-like modulation of the antiferromagnetic gap, suggest an intimate
interrelation between the antiferromagnetic insulator and the superconductor
with its d-wave gap. It is shown here that a projected SO(5) theory, which
explicitly takes the Mott-Hubbard gap into account, correctly describes the
observed gap characteristics. Specifically, it accounts for the order of
magnitude difference between the antiferromagnetic gap modulation and the
superconducting gap and is also consistent with the gap dispersion.


title:
Partitioning of a polymer chain between two confining cavities: the role
  of electrostatic interactions

abstract:
  A recently developed lattice field theory approach to the statistical
mechanics of charged polymers in electrolyte solutions [S. Tsonchev, R. D.
Coalson, and A. Duncan, Phys. Rev. E {\bf{60}}, 4257, (1999)] is generalized to
the case where ground-state dominance in the polymer's Green's function does
not apply. The full mean-field equations for the system are derived and are
shown to possess a unique solution. The approach is applied to the problem of a
charged Gaussian polymer chain confined to move within the region defined by
two fused spheres. The failure of the notion of ground-state dominance under
certain conditions even in the limit of large number of monomers is
demonstrated.


title: Engineering Superconducting Phase Qubits

abstract:
  The superconducting phase qubit combines Josephson junctions into
superconducting loops and defines one of the promising solid state device
implementations for quantum computing. While conventional designs are based on
magnetically frustrated superconducting loops, here we discuss the advantages
offered by $\pi$-junctions in obtaining naturally degenerate two-level systems.
Starting from a basic five-junction loop, we show how to construct degenerate
two-level junctions and superconducting phase switches. These elements are then
effectively engineered into a superconducting phase qubit which operates
exclusively with switches, thus avoiding permanent contact with the environment
through external biasing. The resulting superconducting phase qubits can be
understood as the macroscopic analogue of the `quiet' s-wave-d-wave-s-wave
Josephson junction qubits introduced by Ioffe {\it et al.} [Nature {\bf 398},
679 (1999)].


title:
A Comment on ``Superconducting-Normal Phase Transition in (Ba1-xKx)BiO3,
  x = 0.40, 0.47'' by B. F. Woodfield, D. A. Wright, R. A. Fisher, N. E.
  Phillips and H. Y. Tang, Phys. Rev. Lett. 83, 4622 (1999)

abstract:
  This comment addresses criticisms of our PRL 82 (1999) p. 4532-4535
(cond-mat/9904288) raised by Woodfield et al. in their recent PRL. We find that
the critical fields in single crystals of Ba1-xKxBiO3 (x = 0.4) have anomalous
temperature dependecies which suggests that the superconducting phase
transition in this material is not of order II.


title: Dynamics of the Local Moment Induced by Nonmagnetic Defects in Cuprates

abstract:
  We present a study of the spin dynamics of magnetic defects induced by Li
substitution of the plane Cu in the normal state of YBa$_2$Cu$_3$O$_{6+x}$. The
fluctuations of the coupled Cu magnetic moments in the vicinity of Li are
probed by near-neighbour $^{89}$Y {\it and} $^7$Li NMR spin lattice relaxation.
The data indicates that the magnetic perturbation fluctuates as a single entity
with a correlation time $\tau$ which scales with the local static
susceptibility. This behaviour is reminiscent of the low $T$ Kondo state of
magnetic impurities in conventional metals. Surprisingly it extends well above
the ``Kondo'' temperature for the underdoped pseudogapped case.


title: Diffusion Monte Carlo study of circular quantum dots

abstract:
  We present ground and excited state energies obtained from Diffusion Monte
Carlo (DMC) calculations, using accurate multiconfiguration wave functions, for
$N$ electrons ($N\le13$) confined to a circular quantum dot. We analyze the
electron-electron pair correlation functions and compare the density and
correlation energies to the predictions of local spin density approximation
theory (LSDA). The DMC estimated change in electrochemical potential as
function of the number of electrons in the dot is compared to that from LSDA
and Hartree-Fock (HF) calculations.


title:
Temperature and field dependence of the phase separation, structure, and
  magnetic ordering in La$_{1-x}$Ca$_x$MnO$_3$, ($x=0.47$, 0.50, and 0.53)

abstract:
  Neutron powder diffraction measurements, combined with magnetization and
resistivity data, have been carried out in the doped perovskite
La$_{1-x}$Ca$_x$MnO$_3$ ($x=0.47$, 0.50, and 0.53) to elucidate the structural,
magnetic, and electronic properties of the system around the composition
corresponding to an equal number of Mn3+ and Mn4+. At room temperature all
three samples are paramagnetic and single phase, with crystallographic symmetry
Pnma. The samples then all become ferromagnetic (FM) at $T_C\approx 265$ K. At
$\sim 230$ K, however, a second distinct crystallographic phase (denoted A-II)
begins to form. Initially the intrinsic widths of the peaks are quite large,
but they narrow as the temperature decreases and the phase fraction increases,
indicating microscopic coexistence. The fraction of the sample that exhibits
the A-II phase increases with decreasing temperature and also increases with
increasing Ca doping, but the transition never goes to completion to the lowest
temperatures measured (5 K) and the two phases therefore coexist in this
temperature-composition regime. Phase A-II orders antiferromagnetically (AFM)
below a N\'{e}el temperature $T_N \approx 160$ K, with the CE-type magnetic
structure. Resistivity measurements show that this phase is a conductor, while
the CE phase is insulating. Application of magnetic fields up to 9 T
progressively inhibits the formation of the A-II phase, but this suppression is
path dependent, being much stronger for example if the sample is field-cooled
compared to zero-field cooling and then applying the field. The H-T phase
diagram obtained from the diffraction measurements is in good agreement with
the results of magnetization and resistivity.


title:
Interface effects on the shot noise in normal metal- d-wave
  superconductor Junctions

abstract:
  The current fluctuation in normal metal / d-wave superconductor junctions are
studied for various orientation of the crystal by taking account of the spatial
variation of the pair potentials. Not only the zero-energy Andreev bound states
(ZES) but also the non-zero energy Andreev bound states influence on the
properties of differential shot noise. At the tunneling limit, the noise power
to current ratio at zero voltage becomes 0, once the ZES are formed at the
interface. Under the presence of a subdominant s-wave component at the
interface which breaks time-reversal symmetry, the ratio becomes 4e


title:
Weak-localization corrections to the conductivity of double quantum
  wells

abstract:
  The weak-localization contribution \delta\sigma(B) to the conductivity of a
tunnel-coupled double-layer electron system is evaluated and its behavior in
weak magnetic fields B perpendicular or parallel to the layers is examined. In
a perpendicular field B, \delta \sigma(B) increases and remains dependent on
tunneling as long as the magnetic field is smaller than \hbar/e D \tau_t, where
D is the in-plane diffusion coefficient and \tau_t the interlayer tunneling
time. If \tau_t is smaller than the inelastic scattering time, a parallel
magnetic field also leads to a considerable increase of the concuctivity
starting with a B**2 law and saturating at fields higher than \hbar/e Z (D
\tau_t)**(1/2), where Z is the interlayer distance. In the limit of coherent
tunneling, when \tau_t is comparable to elastic scattering time, \delta
\sigma(B) differs from that of a single-layer system due to ensuing
modifications of the diffusion coefficient. A possibility to probe the
weak-localization effect in double-layer systems by the dependence of the
conductivity on the gate-controlled level splitting is discussed.


title: Proposal For A Quantum Hall Pump

abstract:
  A device is proposed that is similar in spirit to the electron turnstile
except that it operates within a quantum Hall fluid. In the integer quantum
Hall regime, this device pumps an integer number of electrons per cycle. In the
fractional regime, it pumps an integer number of fractionally charged
quasiparticles per cycle. It is proposed that such a device can make an
accurate measurement of the charge of the quantum Hall effect quasiparticles.


title:
Quantum kinetic theory for dense Coulomb systems in strong
  electromagnetic fields

abstract:
  A quantum kinetic theory for correlated charged-particle systems in strong
time-dependent electromagnetic fields is developed. Our approach is based on a
systematic gauge-invariant nonequilibrium Green's functions formulation. We
concentrate on the selfconsistent treatment of dynamical screening and
electromagnetic fields which is applicable to arbitrary nonequilibrium
situations. Numerical results for the nonlinear plasma heating by the laser
field and the electron-ion collision frequency including multi-photon
absorption (inverse bremsstrahlung) are presented.


title:
Probing the statistical properties of Bose-Einstein condensates with
  light

abstract:
  A scattering of short, weak, nonresonant laser pulses on a Bose-Einstein
condensate is proposed as a tool for studying its statistical properties. We
show in particular that the variance of the number of scattered photons may
distinguish between the Poisson and microcanonical statistics.


title: Full-Potential LMTO: Total Energy and Force Calculations

abstract:
  The essential features of a full potential electronic structure method using
Linear Muffin-Tin Orbitals (LMTOs) are presented. The electron density and
potential in the this method are represented with no inherent geometrical
approximation. This method allows the calculation of total energies and forces
with arbitrary accuracy while sacrificing much of the efficiency and physical
content of approximate methods such as the LMTO-ASA method.


title:
Excited States Calculated by Means of the Linear Muffin-Tin Orbital
  Method

abstract:
  The most popular electronic structure method, the linear muffin-tin orbital
method (LMTO), in its full-potential (FP) and relativistic forms has been
extended to calculate the spectroscopic properties of materials form first
principles, i.e, optical spectra, x-ray magnetic circular dichroism (XMCD) and
magneto-optical kerr effect (MOKE). The paper describes an overview of the
FP-LMTO basis set and the calculation of the momentum matrix elements. Some
applications concerning the computation of optical properties of semiconductors
and XMCD spectra of transition metal alloys are reviewed.


title:
Delocalization of states in two component superlattices with correlated
  disorder

abstract:
  Electron and phonon states in two different models of intentionally
disordered superlattices are studied analytically as well as numerically. The
localization length is calculated exactly and we found that it diverges for
particular energies or frequencies, suggesting the existence of delocalized
states for both electrons and phonons. Numerical calculations for the
transmission coefficient support the existence of these delocalized states.


title:
Energy spectra, wavefunctions and quantum diffusion for quasiperiodic
  systems

abstract:
  We study energy spectra, eigenstates and quantum diffusion for one- and
two-dimensional quasiperiodic tight-binding models. As our one-dimensional
model system we choose the silver mean or `octonacci' chain. The
two-dimensional labyrinth tiling, which is related to the octagonal tiling, is
derived from a product of two octonacci chains. This makes it possible to treat
rather large systems numerically. For the octonacci chain, one finds singular
continuous energy spectra and critical eigenstates which is the typical
behaviour for one-dimensional Schr"odinger operators based on substitution
sequences. The energy spectra for the labyrinth tiling can, depending on the
strength of the quasiperiodic modulation, be either band-like or fractal-like.
However, the eigenstates are multifractal. The temporal spreading of a
wavepacket is described in terms of the autocorrelation function C(t) and the
mean square displacement d(t). In all cases, we observe power laws for C(t) and
d(t) with exponents -delta and beta, respectively. For the octonacci chain,
0<delta<1, whereas for the labyrinth tiling a crossover is observed from
delta=1 to 0<delta<1 with increasing modulation strength. Corresponding to the
multifractal eigenstates, we obtain anomalous diffusion with 0<beta<1 for both
systems. Moreover, we find that the behaviour of C(t) and d(t) is independent
of the shape and the location of the initial wavepacket. We use our results to
check several relations between the diffusion exponent beta and the fractal
dimensions of energy spectra and eigenstates that were proposed in the
literature.


title: New Solutions of the T-Matrix Theory of the Attractive Hubbard Model

abstract:
  This short paper summarizes a calculational method for obtaining the
dynamical properties of many-body theories formulated in terms of
(unrenormalized) bare propagators (and more generally, in terms of meromorphic
functions, or convolutions over meromorphic functions) to a very high accuracy.
We demonstrate the method by applying it to a T-matrix theory of the attractive
Hubbard model in two dimensions. We expand the pair propagator using a partial
fraction decomposition, and then solve for the residues and pole locations of
such a decomposition using a computer algebra system to an arbitrarily high
accuracy (we used MapleV and obtained these quantities to a relative error of
10^(-80)). Thus, this method allows us to bypass all inaccuracies associated
with the traditional analytical continuation problem. Our results for the
density of states make clear the pronounced development of a pseudogap as the
temperature is lowered in this formulation of the attractive Hubbard model.


title:
Segregation and charge-density-wave order in the spinless
  Falicov-Kimball model

abstract:
  The spinless Falicov-Kimball model is solved exactly in the limit of
infinite-dimensions on both the hypercubic and Bethe lattices. The competition
between segregation, which is present for large U, and charge-density-wave
order, which is prevalent at moderate U, is examined in detail. We find a rich
phase diagram which displays both of these phases. The model also shows
nonanalytic behavior in the charge-density-wave transition temperature when U
is large enough to generate a correlation-induced gap in the single-particle
density of states.


title:
Aluminum Single Electron Transistors with Islands Isolated from a
  Substrate

abstract:
  The low-frequency noise figures of single-electron transistors
(electrometers) of traditional planar and new stacked geometry were compared.
We observed a correlation between the charge noise and the contact area of the
transistor island with a dielectric substrate in the set of Al transistors
located on the same chip and having almost similar electric parameters. We have
found that the smaller the contact area the lower the noise level of the
transistor. The lowest noise value 8*10E-6 e/sqrt(Hz) at f = 10 Hz. has been
measured in a stacked transistor with an island which was completely isolated
from a substrate. Our measurements have unambiguously indicated that the
dominant source of the background charge fluctuations is associated with a
dielectric substrate


title:
Why have no manifestations of the excitonic mechanism have been detected
  in Ginzburg sandwiches?

abstract:
  The Ginzburg sandwich is a superconducting film coated with a dielectric
layer containing Bose-type exitations, i.e. exitons. Using spatially
inhomogeneous Eliashberg equations in the local interaction limit, an exact
result for the superconducting transition temperature of the Ginzburg sandwich
has been obtained in the first order in a/L (where a is interatomic distance
and L is the film thickness). The result has been found to be independent of
the exiton frequency. The exitonic mechanism appears only in the second order
in a/L since both partners of the Cooper pair should enter a layer of thickness
\sim a in order to interact through exchange of exitons. Numerical estimates
indicate that manifestations of the exitonic mechanism are practically
undetectable in systems with L>>a. Calculations for a narrow-gap and wide-gap
dielectric have been performed and compared to experimental data.


title:
Viscous Flow and Jump Dynamics in Molecular Supercooled Liquids: I
  Translations

abstract:
  We study the transport and the relaxation properties of a molecular
supercooled liquid by molecular-dynamics numerical simulations. The focus is on
the translational motion. Jump motion is detected. At lower temperature the
Stokes-Einstein law breaks down.


title: Absence of Thermodynamic Phase Transition in a Model Glass Former

abstract:
  The glass transition can simply be viewed as the point at which the viscosity
of a structurally disordered liquid reaches 10^{13} Poise [1]. This definition
is operational but it sidesteps fundamental controversies about the glass: Is
the transition a purely dynamical phenomenon [2]? This would mean that
ergodicity gets broken, but that thermodynamic properties of the liquid remain
unchanged across the transition if determined as thermodynamic equilibrium
averages over the whole phase space. The opposite view [3-6] claims that an
underlying thermodynamic phase transition is responsible for the dramatic
slowdown at the liquid-glass boundary. Such a phase transition (which shows up
in proper equilibrium phase space averages) would trigger the dynamic
standstill, and then get masked by it. A recent Monte Carlo algorithm [7]
introduces non-local moves for hard-core systems in a way which preserves
micro-reversibility. Here we use this method to equilibrate a two-dimensional
hard disc system far within its glassy phase. We show that indications of a
thermodynamic transition are lacking up to very high densities, and that the
glass is indistinguishable from the liquid on purely thermodynamic grounds.


title:
Viscous Flow and Jump Dynamics in Molecular Supercooled Liquids: II
  Rotations

abstract:
  The rotational dynamics of a supercooled molecular liquid is investigated by
a molecular-dynamics numerical study. We detect rotational jumps with a
waiting-time distribution which is well fitted by a truncated power law. At
lower temperatures the rotational correlation times are decoupled from the
viscosity.


title:
The Role of Splayed Disorder and Channel Flow on the Dynamics of Driven
  3D Vortices

abstract:
  We present the results of three-dimensional molecular dynamics simulations of
vortices which indicate that, for B greater than the matching field, the
enhanced pinning effectiveness of splayed columnar defects relative to vertical
columnar defects can be explained in terms of the existence or absence of
channels through which the vortices can flow without encountering defects.


title:
Reversible Random Sequential Adsorption of Dimers on a Triangular
  Lattice

abstract:
  We report on simulations of reversible random sequential adsorption of dimers
on three different lattices: a one-dimensional lattice, a two-dimensional
triangular lattice, and a two-dimensional triangular lattice with the nearest
neighbors excluded. In addition to the adsorption of particles at a rate K+, we
allow particles to leave the surface at a rate K-. The results from the
one-dimensional lattice model agree with previous results for the continuous
parking lot model. In particular, the long-time behavior is dominated by
collective events involving two particles. We were able to directly confirm the
importance of two-particle events in the simple two-dimensional triangular
lattice. For the two-dimensional triangular lattice with the nearest neighbors
excluded, the observed dynamics are consistent with this picture. The
two-dimensional simulations were motivated by measurements of Ca++ binding to
Langmuir monolayers. The two cases were chosen to model the effects of changing
pH in the experimental system.


title: Simultaneous quantization of edge and bulk Hall conductivity

abstract:
  The edge Hall conductivity is shown to be an integer multiple of $e^2/h$
which is almost surely independent of the choice of the disordered
configuration. Its equality to the bulk Hall conductivity given by the
Kubo-Chern formula follows from K-theoretic arguments. This leads to
quantization of the Hall conductance for any redistribution of the current in
the sample. It is argued that in experiments at most a few percent of the total
current can be carried by edge states.


title: Mesoscopic Physics of Granular Flows

abstract:
  We present a description of granular dynamics based on the idea of
differentiation between fluid and solid components. First, we construct a model
of completely fluidized phase. Then we discuss a shear surface motion on the
boundary of the bulk solid phase, induced by a moving wall. Our results include
the thickness dependence of the velocity of a developed avalanche, density and
velocity profiles in granular Couette flow experiment.


title: Slow dynamics of stepped surfaces

abstract:
  Two kinds of configurations involving steps on surfaces are reviewed. The
first one results from an initially planar vicinal surface, i.e. slightly
deviating from a high-symmetry (001) or (111) orientation. In some cases, these
surfaces separate into domains of different orientations by a mechanism which
is very similar to phase separation in mixtures. The domain size initially
increases with time and goes to a finite limit, whose value is related to
elastic phenomena. The second kind of configurations results from making
grooves in a high-symmetry surface. The surface smoothes out and takes an
intermediate shape with facet-like hills and valleys, which are the source of a
controversy which we try to clarify as much as possible.


title:
First Principles Study of Carbon Monoxide Adsorption on
  Zirconia-Supported Copper

abstract:
  We have calculated the adsorption energy of carbon monoxide on a monolayer of
copper adsorbed on the (111) face of cubic zirconia. We investigate the
structural parameters of three phases of bulk zirconia (cubic, tetragonal, and
monoclinic) and find excellent agreement with experiment. We have also analyzed
the structural relaxation of both the stoichiometric and reduced (111) surfaces
of cubic zirconia ($c$-ZrO$_2$). For adsorption of copper on $c$-ZrO$_2$, we
find that the preferred binding site is atop the terminal oxygen atom, favored
by 0.3 eV over other high symmetry sites. We compare CO adsorption on
zirconia-supported copper to the results of carbon monoxide on copper (100) (S.
P. Lewis and A. M. Rappe, J. Chem. Phys. {\bf 110}, 4619,(1999).) and show that
adsorption on oxide-supported copper is over 0.2 eV more stable than adsorption
on the bare surface.


title:
Field-theory computation of charge-density oscillations in a
  Tomonaga-Luttinger model with impurities

abstract:
  We compute the charge-density oscillations in a Tomonaga-Luttinger model with
impurities for a short-range electron-electron potential.

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


title:
Low temperature acoustic properties of amorphous silica and the
  Tunneling Model

abstract:
  Internal friction and speed of sound of a-SiO(2) was measured above 6 mK
using a torsional oscillator at 90 kHz, controlling for thermal decoupling,
non-linear effects, and clamping losses. Strain amplitudes e(A) = 10^{-8} mark
the transition between the linear and non-linear regime. In the linear regime,
excellent agreement with the Tunneling Model was observed for both the internal
friction and speed of sound, with a cut-off energy of E(min) = 6.6 mK. In the
non-linear regime, two different behaviors were observed. Above 10 mK the
behavior was typical for non-linear harmonic oscillators, while below 10 mK a
different behavior was found. Its origin is not understood.


title: Spin diffusion in doped semiconductors

abstract:
  The behavior of spin diffusion in doped semiconductors is shown to be
qualitatively different than in undoped (intrinsic) ones. Whereas a spin packet
in an intrinsic semiconductor must be a multiple-band disturbance, involving
inhomogeneous distributions of both electrons and holes, in a doped
semiconductor a single-band disturbance is possible. For n-doped nonmagnetic
semiconductors the enhancement of diffusion due to a degenerate electron sea in
the conduction band is much larger for these single-band spin packets than for
charge packets, and can exceed an order of magnitude at low temperatures even
for equilibrium dopings as small as 10^16 cm^-3. In n-doped ferromagnetic and
semimagnetic semiconductors the motion of spin packets polarized antiparallel
to the equilibrium carrier spin polarization is predicted to be an order of
magnitude faster than for parallel polarized spin packets. These results are
reversed for p-doped semiconductors.


title:
Exact electronic Green functions in a Luttinger liquid with long-range
  interactions

abstract:
  We compute the 2-point (equal-time) electronic Green function in a
Tomonaga-Luttinger system with long-range electron-electron interactions. We
obtain an analytical expression for a "super long-range" potential of the form
$V(x)=\frac{e^2d^{-\epsilon}}{|x|^{1-\epsilon}}$. As a consistency check of our
computational technique we also consider the particular case of a Coulomb
potential. Our result confirms the $\exp-C(logx)^{3/2}$ long-distance behavior
first obtained by Schulz.


title:
High-Field Quasiparticle Tunneling in Bi_2Sr_2CaCu_2O_8+delta: Negative
  Magnetoresistance in the Superconducting State

abstract:
  We report on the c-axis resistivity rho_c(H) in Bi_2Sr_2CaCu_2O_{8+\delta}
that peaks in quasi-static magnetic fields up to 60 T. By suppressing the
Josephson part of the two-channel (Cooper pair/quasiparticle) conductivity
\sigma_c (H), we find that the negative slope of \rho_c(H) above the peak is
due to quasiparticle tunneling conductivity \sigma_q(H) across the CuO_2 layers
below H_{c2}. At high fields (a) \sigma_q(H) grows linearly with H, and (b)
\rho_c(T) tends to saturate (sigma_c \neq 0) as T->0, consistent with the
scattering at the nodes of the d-gap. A superlinear sigma_q(H) marks the normal
state above T_c.


title:
The local spectrum of a superconductor as a probe of interactions
  between magnetic impurities

abstract:
  Qualitative differences in the spectrum of a superconductor near magnetic
impurity pairs with moments aligned parallel and antiparallel are derived. A
proposal is made for a new, nonmagnetic scanning tunneling spectroscopy of
magnetic impurity interactions based on these differences. Near parallel
impurity pairs the mid-gap localized spin-polarized states associated with each
impurity hybridize and form bonding and anti-bonding molecular states with
different energies. For antiparallel impurity moments the states do not
hybridize; they are degenerate.


title:
Effective "Penetration Depth" in the Vortex State of a d-wave
  Superconductor

abstract:
  The temperature and field dependence of the effective magnetic penetration
depth in the vortex state of a d-wave superconductor, as measured by muon spin
rotation experiments, is calculated using a nonlocal London model. We show that
at temperatures below T^* \propto \sqrt{B}, the linear T-dependence of the
effective penetration depth crosses over to a T^3-dependence. This could
provide an explanation for the low temperature flattening of the effective
penetration depth curves observed in a recent muon spin rotation experiment.


title:
Re-examination of electronic transports through a quantum wire coupled
  to a quantum dot

abstract:
  In this paper we re-examine the problem of electronic transports through a
system consisting of a quantum dot which has well-defined discrete energy
levels connected to an infinite quantum wire, using the bosonization method and
phase shift representation, we show that all previously known results can be
obtained through our method in a very simple way. Furthermore, the evolution of
the system from ultraviolet to infrared critical fixed points appears naturally
our method.


title: Quantum Conductance of the Single Electron Transistor

abstract:
  The quantum conductance of the single-electron tunneling (SET) transistor is
investigated in this paper by the functional integral approach. The formalism
is valid for arbitrary tunnel resistance of the junctions forming the SET
transistor at any temperature. The path integrals are evaluated by the
semiclassical method to yield an explicit non-perturbation form of the quantum
conductance of the SET transistor. An anomaly of the quantum conductance is
found if the tunnel resistances are much smaller than the quantum resistance.
The dependence of the conductance on the gate voltage is also discussed.


title:
Metastability and nucleation in the dilute fluid phase of a simple model
  of globular proteins

abstract:
  The dilute fluid phase of model globular proteins is studied. The model
possesses a fluid-fluid transition buried within the fluid-crystal coexistence
region, as do some globular proteins. If this fluid-fluid transition is not
buried deep inside the fluid-crystal coexistence region the crystalline phase
does not nucleate within the dilute fluid. We link this lack of nucleation of
the crystal to the interactions in our model and speculate that similar
interactions between globular proteins are responsible for the difficulty found
in crystallising many globular proteins.


title: Low-energy behavior of the spin-tube and spin-orbital models

abstract:
  The low-energy effective Hamiltonian of three coupled spin chains with
periodic boundary conditions (spin tube) is expressed, in the limit of strong
interchain coupling, in terms of XXZ chains coupled by biquadratic exchange
interaction. A similar class of models was proposed to describe the coupling of
spins to orbital degrees of freedom in materials such as NaV2O5. We investigate
these models by means of bosonization and renormalization group techniques, and
find that the generic phase diagram comprises a gapless region and gapped
regions consisting of a spin liquid phase and various antiferromagnetic phases.
We discuss the properties of the spin liquid phase, in particular the nature of
the ground state and of the elementary excitations above it. We then study the
effect of a magnetic field, and conclude that a strong enough magnetic field
can suppress the dimerized phase leading to a two component Luttinger liquid.
The critical exponents at the transition gapful-gapless are calculated and
shown to be non-universal in the spin tube case as well as in the generic spin
orbital problem.


title: p>2 spin glasses with first order ferromagnetic transitions

abstract:
  We consider an infinite-range spherical p-spin glass model with an additional
r-spin ferromagnetic interaction, both statically using a replica analysis and
dynamically via a generating functional method. For r>2 we find that there are
first order transitions to ferromagnetic phases. For r<p there are two
ferromagnetic phases, one non-glassy replica symmetric and one exhibiting
glassy one-step replica symmetry breaking and aging, whereas for r>=p only the
replica symmetric phase exists.


title: Total energy density as an interpretative tool

abstract:
  We present an unambiguous formulation for the total energy density within
density-functional theory. We propose that it be used as a tool for the
interpretation of computed energy and electronic structure changes during
structural transformations and chemical reactions, augmenting the present use
of electron density changes and changes in the Kohn-Sham local density of
states and Kohn-Sham energy density.


title:
The Relation of Neutron Incommensurability to Electronic Structure in
  High Temperature Superconductors

abstract:
  The relation between the incommensurability observed in neutron scattering
experiments in bilayer cuprate superconductors and the electronic structure is
investigated. It is found that the observed incommesurability pattern, as well
as its dependence on energy, can be well reproduced by electronic dispersions
motivated by angle resolved photoemission data. The commensurate resonance and
its contribution to the superconducting condensation energy are discussed in
the context of these calculations.


title:
Exciton magnetotransport in two-dimensional systems: Weak-localization
  effects

abstract:
  We consider the effect of a magnetic field $B$ on the transport of neutral
composite particles, excitons, in weakly disordered 2D systems. In the case of
classical transport, when the interference of different paths is neglected, the
magnetic field suppresses exciton transport, and the static diffusion constant
$D(B)$ monotonically drops with $B$. When quantum-mechanical corrections due to
weak localization are taken into account, $D(B)$ becomes a nonmonotonic
function of $B$. In weak magnetic fields, where the magnetic length is much
larger than the exciton Bohr radius, $l_B >> a_B$, a positive magnetodiffusion
effect is predicted, i.e., the exciton mobility should increase with $B$.


title: Magnetization Plateaus in a Solvable 3-Leg Spin Ladder

abstract:
  We present a solvable ladder model which displays magnetization plateaus at
fractional values of the total magnetization. Plateau signatures are also shown
to exist along special lines. The model has isotropic Heisenberg interactions
with additional many-body terms. The phase diagram can be calculated exactly
for all values of the rung coupling and the magnetic field. We also derive the
anomalous behaviour of the susceptibility near the plateau boundaries. There is
good agreement with the phase diagram obtained recently for the pure Heisenberg
ladders by numerical and perturbative techniques.


title:
Spin Anisotropy and Quantum Hall Effect in the Kagome Lattice - Chiral
  Spin State based on a Ferromagnet-

abstract:
  A ferromagnet with spin anisotropies on the 2D Kagome lattice is
theoretically studied. This is a typical example of the flat-band ferromagnet.
The Berry phase induced by the tilting of the spins opens the band gap and
quantized Hall conductance \sigma_{xy}=\pm e^2/h is realized without external
magnetic field. This is the most realistic chiral spin state based on the
ferromagnetism. We also discuss the implication of our results to anomalous
Hall effect observed in the metallic pyrochlore ferromagnets R_2Mo_2O_7(R=Nd,
Sm, Gd).


title: Equilibrium and Aging Dynamics of Simple Models for Glasses

abstract:
  We analyze the properties of the energy landscape of {\it finite-size} fully
connected $p$-spin-like models. In the thermodynamic limit the high temperature
phase is described by the schematic Mode Coupling Theory of super-cooled
liquids. In this limit the barriers between different basins are infinite below
the critical dynamical temperature the ergodicity is broken on in infinite
times. We show that {\it finite-size} fully connected $p$-spin-like models,
where activated processes are possible, do exhibit properties typical of real
super-cooled liquid when both are near the critical glass transition. Our
results support the conclusion that fully-connected $p$-spin-like models are
the natural statistical mechanical models for studying the glass transition in
super-cooled liquids.


title: Formation of heavy quasiparticle state in two-band Hubbard model

abstract:
  A realization of heavy fermion state is investigated on the basis of two-band
Hubbard model. By means of the slave-boson mean-field approximation, it is
shown that for the intermediate electron density, n_e=1.5, the inter-band
Coulomb repulsion U strongly emphasizes initially small difference between
bands, and easily stabilizes integral valence in the lower band. As a result, a
strong renormalization takes place in the lower band and the mixing strength
between two bands. It gives rise to a sharp peak at the Fermi level in the
quasiparticle density of states, as that obtained in the periodic Anderson
model. In contrast to a simple insight that the Hund's-rule coupling J reduces
the characteristic energy, it turns out to be almost irrelevant to the
renormalization for J<U. The required conditions are suitable for LiV_2O_4, the
first observed heavy fermion compound in transition metal oxide.


title: Scaling and Fractal formation in Persistence

abstract:
  The spatial distribution of unvisited/persistent sites in $d=1$
$A+A\to\emptyset$ model is studied numerically. Over length scales smaller than
a cut-off $\xi(t)\sim t^{z}$, the set of unvisited sites is found to be a
fractal. The fractal dimension $d_{f}$, dynamical exponent $z$ and persistence
exponent $\theta$ are related through $z(1-d_{f})=\theta$. The observed values
of $d_{f}$ and $z$ are found to be sensitive to the initial density of
particles. We argue that this may be due to the existence of two competing
length scales, and discuss the possibility of a crossover at late times.


title:
Temperature Dependence of Spin and Bond Ordering in a Spin-Peierls
  System

abstract:
  We investigate thermodynamic properties of a one-dimensional S=1/2
antiferromagnetic Heisenberg model coupled to a lattice distortion by a quantum
Monte Carlo method. In particular we study how spin and lattice dimerize as a
function of the temperature, which gives a fundamental process of the
spin-Peierls transition in higher dimensions. The degree of freedom of the
lattice is taken into account adiabatically and the thermal distribution of the
lattice distortion is obtained by the thermal bath algorithm. We find that the
dimerization develops as the temperature decreases and it converges to the
value of the dimerization of the ground state at T=0. Furthermore we find that
the coupling constants of spins fluctuate quite largly at high temperature and
there thermodynamic properties deviate from those of the uniform chain. Doping
of non-magnetic impurities causes cut of the chain into short chains with open
boundary. We investigate thermodynamic properties of open chains taking
relaxation of the lattice into consideration. We find that strong bonds locate
at the edges and a defect of the bond alternation appears in the chain with odd
number of sites, which causes enhancement of the staggered magnetic order. We
find a spreaded staggered structure which indicates that the defect moves
diffusively in the chain even at very low temperature.


title:
Simulated nuclear spin-lattice relaxation in Heisenberg ferrimagnets:
  Indirect observation of quadratic dispersion relations

abstract:
  In response to recent proton spin relaxation-time measurements on
NiCu(pba)(H$_2$O)$_3$$\cdot$2H$_2$O with ${pba}=1,3{-propylenebis(oxamato)}$,
which is an excellent one-dimensional ferrimagnetic Heisenberg model system of
spin-$(1,{1/2})$, we study the Raman relaxation process in spin-$(S,s)$ quantum
ferrimagnets on the assumption of predominantly dipolar hyperfine interactions
between protons and magnetic ions. The relaxation time $T_1$ is formulated
within the spin-wave theory and is estimated as a function of temperature and
an applied field $H$ by a quantum Monte Carlo method. The low-temperature
behavior of the relaxation rate $T_1^{-1}$ qualitatively varies with $(S,s)$,
while $T_1^{-1}$ is almost proportional to $H^{-1/2}$ due to the characteristic
dispersion relations.


title:
Competing Ground States of the New Class of Halogen-Bridged Metal
  Complexes

abstract:
  Based on a symmetry argument, we study the ground-state properties of
halogen-bridged binuclear metal chain complexes. We systematically derive
commensurate density-wave solutions from a relevant two-band Peierls-Hubbard
model and numerically draw the the ground-state phase diagram as a function of
electron-electron correlations, electron-phonon interactions, and doping
concentration within the Hartree-Fock approximation. The competition between
two types of charge-density-wave states, which has recently been reported
experimentally, is indeed demonstrated.


title: Local fields in nonlinear quantum transport

abstract:
  We investigate the dynamical interplay between currents and electromagnetic
fields in frequency-dependent transport through a single-channel quantum wire
with an impurity potential in the presence of electron-electron interactions.
We introduce and discuss a formalism which allows a self-consistent treatment
of currents and electromagnetic fields.


title:
Quantum Impurities and the Neutron Resonance Peak in ${\bf YBa_2 Cu_3
  O_7}$: Ni versus Zn

abstract:
  The influence of magnetic (S=1) and nonmagnetic (S=0) impurities on the spin
dynamics of an optimally doped high temperature superconductor is compared in
two samples with almost identical superconducting transition temperatures:
YBa$_2$(Cu$_{0.97}$Ni$_{0.03}$)$_3$O$_7$ (T$_c$=80 K) and
YBa$_2$(Cu$_{0.99}$Zn$_{0.01}$)$_3$O$_7$ (T$_c$=78 K). In the Ni-substituted
system, the magnetic resonance peak (which is observed at E$_r \simeq$40 meV in
the pure system) shifts to lower energy with a preserved E$_r$/T$_c$ ratio
while the shift is much smaller upon Zn substitution. By contrast Zn, but not
Ni, restores significant spin fluctuations around 40 meV in the normal state.
These observations are discussed in the light of models proposed for the
magnetic resonance peak.


title:
The spin-orbit interaction as a source of new spectral and transport
  properties in quasi-one-dimensional systems

abstract:
  We present an exact theoretical study of the effect of the spin-orbit (SO)
interaction on the band structure and low temperature transport in long
quasi-one-dimensional electron systems patterned in two-dimensional electron
gases in zero and weak magnetic fields. We reveal the manifestations of the SO
interaction which cannot in principle be observed in higher dimensional
systems.


title:
Effect of Time Reversal Symmetry Breaking on the Density of States in
  Small Superconducting Grains

abstract:
  We show that in ultra-small superconducting grains any concentration of
magnetic impurities or infinitely small orbital effect of magnetic field leads
to destruction of the hard gap in the tunneling density of states. Instead,
though exponentially suppressed at low energies, the tunneling density of
states exhibits the ``soft gap'' behavior, vanishing linearly with excitation
energy, as the energy approaches zero.


title:
Time-Dependent Variational Analysis of Josephson Oscillations in a
  Two-component Bose-Einstein Condensate

abstract:
  The dynamics of Josephson-like oscillations between two coupled Bose-Einstein
condensates is studied using the time-dependent variational method. We suppose
that the quantum state of the condensates is a gaussian wave-packet which can
translate and perform breathing shape oscillations. Under this hypotheses we
study the influence of these degrees of freedom on the tunneling dynamics by
comparing the full-model with one where these degrees of freedom are ``frozen''
at its equilibrium values. The result of our calculation shows that when the
traps are not displaced the two models agree, whereas when they are, the models
differ considerably, the former being now closer to its linear approximation.


title:
Conformal field theory and edge excitations for the principal series of
  quantum Hall fluids

abstract:
  Motivated by recent experimental results, we reconsider the theory of the
edge excitations for the fractional Hall effect at filling factors
$\nu=p/(2np+1)$. We propose to modify the standard $u(1)\otimes su(p)$ edge
theory for this series by introducing twist fields which change the boundary
conditions of the bosonic fields and simulate the effect of fractions of flux
quanta $\phi_0/p$. This has the effect of removing the conserved charges
associated to the neutral modes while keeping the right statistics of the
particles. The Green function of the electron in presence of twists decays at
long distance with an exponent varying continuously with $\nu$.


title:
From Neel long-range order to spin-liquids in the multiple-spin exchange
  model

abstract:
  The phase diagram of the multiple-spin exchange model on the triangular
lattice is studied using exact diagonalizations. The two-spin (J_2) and
four-spin (J_4) exchanges have been taken into account for 12, 16, 19, 21, 24,
and 27 site samples in the parameter region J_4=0 - 0.25 (for a fixed J_2=1).
It is found that the three-sublattice N\'eel ordered state built up by the pure
two-spin exchange can be destroyed by the four-spin exchange, forming a
spin-liquid state. The different data suggest that the phase diagram in this
range of parameters exhibits two phases. The pure J_2 phase is a
three-sublattice Neel ordered phase, a small J_4 drives it into a spin-liquid
state with a spin gap filled of a large number of singlets. This spin-liquid
phase is not of the same generic kind as the phase studied by Misguich et al.
[Phys. Rev. B 60, 1064 (1999)]. It is observed on the finite-size samples that
the spin liquid phase, as the Neel ordered phase, exhibits a magnetization
plateau at m = 1/3, and for J_4 >0.15 a second plateau atm=1/2. These two
plateaus are associated respectively to the semi-classical orderings uud and
uuud.


title:
Comment on `Ising Pyrochlore Magnets: Low Temperature Properties, ``Ice
  Rules,'' and Beyond' by R. Siddharthan et al., Phys. Rev. Lett. 83, 1854
  (1999)

abstract:
  In this Comment we argue that Ho$_2$Ti$_2$O$_7$ does not exhibit a transition
to a partially ordered state unlike what is argued in PRL 83, 1854 (1999), that
it exhibits spin ice behavior, and that the experimental specific heat data by
Siddharthan et al. can be accounted for in terms of a "dipolar spin ice" model
by including an expected contibution from the nuclear Ho spins to the
appropriate long-range treatment of the dipole-dipole interactions.


title:
Reply to ``Comment on `Inverse exciton series in the optical decay of an
  excitonic molecule' "

abstract:
  As a reply to the Comment by I.S. Gorban {\it et al.} (Phys. Rev. B,
preceding paper) we summarize our criticism on their claim of the first
observation of the $M$ series in $\beta$-ZnP$_2$. We support our analysis by
reporting the first observation of inverse {\it polariton} series from the
excitonic molecules selectively generated at ${\bf K}_m \simeq {\bf 0}$ in a
CuCl single crystal. This observation and its explanation within the
bipolariton model complete our proof of the biexcitonic origin of the inverse
series.


title:
Numerical renormalization group of vortex aggregation in 2D decaying
  turbulence: the role of three-body interactions

abstract:
  In this paper, we introduce a numerical renormalization group procedure which
permits long-time simulations of vortex dynamics and coalescence in a 2D
turbulent decaying fluid. The number of vortices decreases as $N\sim t^{-\xi}$,
with $\xi\approx 1$ instead of the value $\xi=4/3$ predicted by a na\"{\i}ve
kinetic theory. For short time, we find an effective exponent $\xi\approx 0.7$
consistent with previous simulations and experiments. We show that the mean
square displacement of surviving vortices grows as $<x^2>\sim t^{1+\xi/2}$.
Introducing effective dynamics for two-body and three-body collisions, we
justify that only the latter become relevant at small vortex area coverage. A
kinetic theory consistent with this mechanism leads to $\xi=1$. We find that
the theoretical relations between kinetic parameters are all in good agreement
with experiments.


title:
Quantitative investigation of the mean-field scenario for the structural
  glass transition from a schematic mode-coupling analysis of experimental data

abstract:
  A quantitative application to real supercooled liquids of the mean-field
scenario for the glass transition ($T_g$) is proposed. This scenario, based on
an analogy with spin-glass models, suggests a unified picture of the
mode-coupling dynamical singularity ($T_c$) and of the entropy crisis at the
Kauzmann temperature ($T_K$), with $T_c>T_g>T_K$. Fitting a simple set of
mode-coupling equations to experimental light-scattering spectra of two fragile
liquids and deriving the equivalent spin-glass model, we can estimate not only
$T_c$, but also the static transition temperature $T_s$ corresponding
supposedly to $T_K$. For the models and systems considered here, $T_s$ is
always found above $T_g$, in the fluid phase. A comparison with recent
theoretical calculations shows that this overestimation of the ability of a
liquid to form a glass seems to be a generic feature of the mean-field
approach.


title:
Low temperature specific heat of the molecular cluster Fe$_{8}$:
  contribution of the local field

abstract:
  We present low temperature specific heat and ac-susceptibility measurements
on Fe$_{8}$ powdered sample. Below 1.3 K, superparamagnetic blocking effects as
well as an excess specific heat contribution are evident. The latter is
attributed to a splitting of the ground state doublet in an inhomogeneous local
field of hyperfine and dipolar origin. The local field contributions are
evident in the resonances observed in the field dependent ac-susceptibility and
specific heat below 0.5 K. The low temperature Schottky contribution allowed us
to check the crystal field parameters of effective spin Hamiltonians, recently
proposed to simulate EPR and inelastic neutron scattering experiments.


title:
Diffusive Growth of a Single Droplet with Three Different Boundary
  Conditions

abstract:
  We study a single, motionless three-dimensional droplet growing by adsorption
of diffusing monomers on a 2D substrate. The diffusing monomers are adsorbed at
the aggregate perimeter of the droplet with different boundary conditions.
Models with both an adsorption boundary condition and a radiation boundary
condition, as well as a phenomenological model, are considered and solved in a
quasistatic approximation. The latter two models allow particle detachment. In
the short time limit, the droplet radius grows as a power of the time with
exponents of 1/4, 1/2 and 3/4 for the models with adsorption, radiation and
phenomenological boundary conditions, respectively. In the long time limit a
universal growth rate as $[t/\ln(t)]^{1/3}$ is observed for the radius of the
droplet for all models independent of the boundary conditions. This asymptotic
behaviour was obtained by Krapivsky \cite{krapquasi} where a similarity
variable approach was used to treat the growth of a droplet with an adsorption
boundary condition based on a quasistatic approximation. Another boundary
condition with a constant flux of monomers at the aggregate perimeter is also
examined. The results exhibit a power law growth rate with an exponent of 1/3
for all times.


title: Search for effective models of stripes in the cuprates

abstract:
  We argue that effective 1D models of stripes in the cuprate superconductors
can be constructed by studying ground states and elementary excitations of
domain walls in 2D model antiferromagnets. This method, applied to the t-J
model with Ising anisotropy, yields two such limiting cases: an ordinary 1D
electron gas and a 1D gas of holons strongly coupled to transversal
fluctuations of the stripe.


title: New Type of Charge and Magnetic order in the Ferromagnetic Kondo Lattice

abstract:
  We study numerically the one dimensional ferromagnetic Kondo lattice, a model
widely used to describe nickel and manganese perovskites. By including a
nearest neighbor Coulomb interaction (V) and a superexchange interaction
between the localized moments (K), we obtain the phase diagram in parameter
space for several dopings at T=0. Due to the competition between double and
superexchange, we find a region where the formation of magnetic polarons
induces a charge ordered (CO) state which survives also for V=0. This mechanism
should be taken into account in theories of charge ordering involving spin
degrees of freedom.


title:
Spontaneous dimer order, excitation spectrum, and quantum phase
  transitions in the J1-J2 Heisenberg model

abstract:
  We overview some recent work and present new results on the ground state
properties and the spectrum of excitations of the two-dimensional frustrated
Heisenberg antiferromagnet. Spontaneous dimer order is present in the quantum
disordered phase of this model. We study the stability and analyze the
structure of the spectrum, including the two-particle singlet excitation branch
throughout the disordered phase, as well as in the vicinity of the Neel
critical point. The variation of the dimer order parameter is also given, and
it is argued that near the critical point it reflects the presence of the
low-energy singlet bound state.


title: On the Quantization of the Monoatomic Ideal Gas

abstract:
  An english translation of the original work of Enrico Fermi on the
quantization of the monoatomic ideal gas, is given in this paper. Fermi
introduced here for the first time the statistical law obeyed by most of the
particles in nature: Fermi-Dirac statistics. The formalism that he used is
based on the quantization of the monoatomic ideal gas in a harmonic trap. This
trappping configuration is similar to that used in current experiments on
trapped Fermi gases.


title: Hydrodynamics of the quantum Hall smectics

abstract:
  We propose a dynamical theory of the stripe phase arising in a
two-dimensional electron liquid near half-integral fillings of high Landau
levels. The system is modelled as a novel type of a smectic liquid crystal with
the Lorentz force dominated dynamics. We calculate the structure factor, the
dispersion relation of the collective modes (magnetophonons), and their
intrinsic attenuation rate. We find strong power-law renormalizations of the
elastic and dissipative coefficients by thermal fluctuations familiar from the
conventional smectics but with different dynamical scaling exponents.


title:
Resonant quantum coherence of magnetization at excited states in
  nanospin systems with different crystal symmetries

abstract:
  The quantum interference effects induced by the Wess-Zumino term, or Berry
phase are studied theoretically in resonant quantum coherence of magnetization
vector between degenerate excited states in nanometer-scale single-domain
ferromagnets in the absence of an external magnetic field. By applying the
periodic instanton method in the spin-coherent-state path integral, we evaluate
the low-lying tunnel splittings between degenerate excited states of
neighboring wells. And the low-lying energy level spectrum of m-th excited
states are obtained with the help of the Bloch theorem in one-dimensional
periodic potential.


title:
Relation between the superconducting gap energy and the two-magnon Raman
  peak energy in Bi2Sr2Ca{1-x}YxCu2O{8+\delta}

abstract:
  The relation between the electronic excitation and the magnetic excitation
for the superconductivity in Bi2Sr2Ca{1-x}YxCu2O{8+\delta} was investigated by
wide-energy Raman spectroscopy. In the underdoping region the B1g scattering
intensity is depleted below the two-magnon peak energy due to the "hot spots"
effects. The depleted region decreases according to the decrease of the
two-magnon peak energy, as the carrier concentration ncreases. This two-magnon
peak energy also determines the B1g superconducting gap energy as $2\Delta
\approx \alpha \hbar \omega_{\rm Two-Magnon} \approx J_{\rm effective}$
$(\alpha=0.34-0.41)$ from under to overdoping hole concentration.


title:
Incommensurate Spin Dynamics in High Temperature Superconductor of
  Optimally Doped YBa2Cu3O7

abstract:
  The spin dynamics of an optimally doped YBa2Cu3O7 (Tc = 93 K) crystal array
have been investigated in a wide range of momentum and energy (Q - E) space
using the time-of-flight neutron scattering method. Incommensurate spin
modulation in Q is a characteristic feature, as it is in the under-doped
YBa2Cu3O6.7 with a different incommensurability. A linear relationship between
the incommensurability and Tc is proposed. Along with the discovery of the same
incommensurability in under-doped La2-ySryCuO4, it may be a generic
characteristic of the high-Tc oxide superconductor.


title: Magnetization Plateau in the Frustrated Spin Ladder

abstract:
  The magnetization process of the S=1/2 antiferromagnetic spin ladder at T=0
is studied by the exact diagonalization of finite clusters and size scaling
analyses. It is found that a magnetization plateau appears at half the
saturation value (m=1/2) in the presence of a sufficiently large
next-nearest-neighbor exchange interaction to yield the frustration, when the
rung coupling is larger than the leg one. The phase diagram at m=1/2 is given
by the analysis based on the conformal invariance. The magnetization curves are
also presented in several cases.


title: Critical exponents in spin glasses : numerics and experiments

abstract:
  We give an overview of numerical and experimental estimates of critical
exponents in Spin Glasses. We find that the evidence for a breakdown of
universality of exponents in these systems is very strong.


title:
Frustrated Hubbard ladders and superconductivity in $\kappa$-BEDT-TTF
  organic compounds

abstract:
  Half-filled two-leg Hubbard ladders have spin-gapped short-range
antiferromagnetic correlations while three-leg ladders have power law
antoferromagnetic correlations, and both systems have d_{x^2-y^2}-power law
pairing correlations when they are doped. Thus these ladders exhibit some of
the phenomenology seen in the layered cuprates. Here we report results for
half-filled frustrated Hubbard ladders, based upon ladder segments taken from a
tight-binding model of kappa-BEDT-TTF. Although these ladders are half-filled,
varying the degree of frustration can drive them across an insulator-metal
transition. We suggest that the spin, charge and pairing correlations of these
frustrated ladders near the insulator-metal transition provide support for the
notion that kappa-BEDT-TTF is a strongly correlated superconductor.


title: Hysteresis in vibrated granular media

abstract:
  Some general dynamical properties of models for compaction of granular media
based on master equations are analyzed. In particular, a one-dimensional
lattice model with short-ranged dynamical constraints is considered. The
stationary state is consistent with Edward's theory of powders. The system is
submitted to processes in which the tapping strength is monotonically increased
and decreased. In such processes the behavior of the model resembles the
reversible-irreversible branches which have been recently obaserved in
experiments. This behavior is understood in terms of the general dynamical
properties of the model, and related to the hysteresis cycles exhibited by
structural glasses in thermal cycles. The existence of a "normal" solution,
i.e., a solution of the master equation which is monotonically approached by
all the other solutions, plays a fundamental role in the understanding of the
hysteresis effects.


title: Noise induced stability in fluctuating, bistable potentials

abstract:
  The over-damped motion of a Brownian particle in an asymmetric, bistable,
fluctuating potential shows noise induced stability: For intermediate
fluctuation rates the mean occupancy of minima with an energy above the
absolute minimum is enhanced. The model works as a detector for potential
fluctuations being not too fast and not too slow. This effect occurs due to the
different time scales in the problem. We present a detailed analysis of this
effect using the exact solution of the Fokker-Planck equation for a simple
model. Further we show that for not too fast fluctuations the system can be
well described by effective rate equations. The results of the rate equations
agree quantitatively with the exact results.


title: Surface defreezing of glasses

abstract:
  A glass surface may still flow below the bulk glass transition temperature,
where the underlying bulk is frozen. Assuming the existence at T=T* of a bulk
thermodynamical glass transition, we show that the glass-vapor interface is
generally wetted by a liquid layer of thickness ~ -ln(T*-T) when T--> T*.
Contrary to standard surface melting of crystals however, the integrated value
of the diffusivity across the interface remains finite for T-->T*. Difference
in shape induced by bulk and by surface flow is discussed as a possible means
of experimental detection of surface defreezing.


title: Metastable states of spin glasses on random thin graphs

abstract:
  In this paper we calculate the mean number of metastable states for spin
glasses on so called random thin graphs with couplings taken from a symmetric
binary distribution $\pm J$. Thin graphs are graphs where the local
connectivity of each site is fixed to some value $c$. As in totally connected
mean field models we find that the number of metastable states increases
exponentially with the system size. Furthermore we find that the average number
of metastable states decreases as $c$ in agreement with previous studies
showing that finite connectivity corrections of order $1/c$ increase the number
of metastable states with respect to the totally connected mean field limit. We
also prove that the average number of metastable states in the limit
$c\to\infty$ is finite and converges to the average number of metastable states
in the Sherrington-Kirkpatrick model. An annealed calculation for the number of
metastable states $N_{MS}(E)$ of energy $E$ is also carried out giving a lower
bound on the ground state energy of these spin glasses. For small $c$ one may
obtain analytic expressions for $<N_{MS}(E)>$.


title: Spinwave damping in the two-dimensional ferromagnetic XY model

abstract:
  The effect of damping of spinwaves in a two-dimensional classical
ferromagnetic XY model is considered. The damping rate $\Gamma_{q}$ is
calculated using the leading diagrams due to the quartic-order deviations from
the harmonic spin Hamiltonian. The resulting four-dimensional integrals are
evaluated by extending the techniques developed by Gilat and others for
spectral density types of integrals. $\Gamma_{q}$ is included into the memory
function formalism due to Reiter and Solander, and Menezes, to determine the
dynamic structure function $S(q,\omega)$. For the infinite sized system, the
memory function approach is found to give non-divergent spinwave peaks, and a
smooth nonzero background intensity (``plateau'' or distributed intensity) for
the whole range of frequencies below the spinwave peak. The background
amplitude relative to the spinwave peak rises with temperature, and eventually
becomes higher than the spinwave peak, where it appears as a central peak. For
finite-sized systems, there are multiple sequences of weak peaks on both sides
of the spinwave peaks whose number and positions depend on the system size and
wavevector in integer units of $2\pi/L$. These dynamical finite size effects
are explained in the memory function analysis as due to either spinwave
difference processes below the spinwave peak or sum processes above the
spinwave peak. These features are also found in classical Monte Carlo --
Spin-Dynamics simulations.


title:
From spatially indirect to momentum-space indirect exciton by in-plane
  magnetic field

abstract:
  In-plane magnetic field is found to change drastically the photoluminescence
spectra and kinetics of interwell excitons in GaAs/AlGaAs coupled quantum
wells. The effect is due to the in-plane magnetic field induced displacement of
the interwell exciton dispersion in a momentum space, which results in the
transition from the momentum-space direct exciton ground state to the
momentum-space indirect exciton ground state. In-plane magnetic field is,
therefore, an effective tool for the exciton dispersion engineering.


title:
Comment on "Quantum Monte Carlo study of the dipole moment of CO" [J.
  Chem. Phys. 110, 11700 (1999)]

abstract:
  Recently Schautz and Flad concluded that the Hellmann-Feynman theorem holds
within the fixed-node diffusion quantum Monte Carlo (DMC) method. We show that
the Hellmann-Feynman expression is not in general equal to the derivative of
the DMC energy with respect to some parameter $\lambda$ if the nodal surface
depends on $\lambda$.


title: Exact dynamical structure factor of the degenerate Haldane-Shastry model

abstract:
  The dynamical structure factor $S(q,\omega)$ of the K-component (K = 2,3,4)
spin chain with the 1/r^2 exchange is derived exactly at zero temperature for
arbitrary size of the system. The result is interpreted in terms of a free
quasi-particle picture which is generalization of the spinon picture in the
SU(2) case; the excited states consist of K quasi-particles each of which is
characterized by a set of K-1 quantum numbers. Divergent singularities of
$S(q,\omega)$ at the spectral edges are derived analytically. The analytic
result is checked numerically for finite systems.

categories: cond-mat.str-el cond-mat.stat-mech hep-th math.RT nlin.SI solv-int


title:
Structure, elastic moduli and thermodynamics of sodium and potassium at
  ultra-high pressures

abstract:
  The equations of state at room temperature as well as the energies of crystal
structures up to pressures exceeding 100 GPa are calculated for Na and K . It
is shown that the allowance for generalized gradient corrections (GGA) in the
density functional method provides a precision description of the equation of
state for Na, which can be used for the calibration of pressure scale. It is
established that the close-packed structures and BCC structure are not
energetically advantageous at high enough compressions. Sharply non-monotonous
pressure dependences of elastic moduli for Na and K are predicted and melting
temperatures at high pressures are estimated from various melting criteria. The
phase diagram of K is calculated and found to be in good agreement with
experiment.


title: Pressure and Maxwell Tensor in a Coulomb Fluid

abstract:
  The pressure in a classical Coulomb fluid at equilibrium is obtained from the
Maxwell tensor at some point inside the fluid, by a suitable statistical
average. For fluids in an Euclidean space, this is a fresh look on known
results. But, for fluids in a curved space, a case which is of some interest,
the unambiguous results from the Maxwell tensor approach have not been obtained
by other methods.


title:
Theory of Scanning Tunneling Spectroscopy of a Magnetic Adatom on a
  Metallic Surface

abstract:
  A comprehensive theory is presented for the voltage, temperature, and spatial
dependence of the tunneling current between a scanning tunneling microscope
(STM) tip and a metallic surface with an individual magnetic adatom. Modeling
the adatom by a nondegenerate Anderson impurity, a general expression is
derived for a weak tunneling current in terms of the dressed impurity Green
function, the impurity-free surface Green function, and the tunneling matrix
elements. This generalizes Fano's analysis to the interacting case. The
differential-conductance lineshapes seen in recent STM experiments with the tip
directly over the magnetic adatom are reproduced within our model, as is the
rapid decay, \sim 10\AA, of the low-bias structure as one moves the tip away
from the adatom. With our simple model for the electronic structure of the
surface, there is no dip in the differential conductance at approximately one
lattice spacing from the magnetic adatom, but rather we see a resonant
enhancement. The formalism for tunneling into small clusters of magnetic
adatoms is developed.


title: Disorder-induced critical behavior in driven diffusive systems

abstract:
  Using dynamic renormalization group we study the transport in driven
diffusive systems in the presence of quenched random drift velocity with
long-range correlations along the transport direction. In dimensions
$d\mathopen< 4$ we find fixed points representing novel universality classes of
disorder-dominated self-organized criticality, and a continuous phase
transition at a critical variance of disorder. Numerical values of the scaling
exponents characterizing the distributions of relaxation clusters are in good
agreement with the exponents measured in natural river networks.


title: Amorphous thin film growth: theory compared with experiment

abstract:
  Experimental results on amorphous ZrAlCu thin film growth and the dynamics of
the surface morphology as predicted from a minimal nonlinear stochastic
deposition equation are analysed and compared. Key points of this study are (i)
an estimation procedure for coefficients entering into the growth equation and
(ii) a detailed analysis and interpretation of the time evolution of the
correlation length and the surface roughness. The results corroborate the
usefulness of the deposition equation as a tool for studying amorphous growth
processes.


title: First-Principles Calculations of Positron Annihilation in Solids

abstract:
  We present first-principles approaches based on density functional theory for
calculating positron states and annihilation characteristics in condensed
matter. The treatment of the electron-positron correlation effects (the
enhancement of the electron density at the positron with respect to mean-field
density) is shown to play a crucial role when calculating the annihilation
rates. A generalized gradient approximation (GGA) takes the strong
inhomogeneities of the electron density in the ion core region into account and
reproduces well the experimental total annihilation rates (inverses of the
positron lifetimes) by suppressing the rates given by a local density
approximation (LDA). The GGA combined with an electron-state-dependent
enhancement scheme gives a good description for the momentum distributions of
the annihilating positron-electron pairs reproducing accurately the trends
observed in the angular correlation (ACAR) or Doppler broadening measurements
of the annihilation radiation. The combination of the present positron lifetime
and momentum density calculations with the corresponding measurements yields a
unique tool for defect identification. Especially, the investigation of various
vacancy-type defects in semiconductors able to trap positrons will be an
important field for these methods. We will show that the identification of
vacancy-impurity complexes in highly n-Type Si and the study of the SiO$_2$/Si
interface are particularly interesting applications.


title:
Neutron scattering study of the field-induced soliton lattice in
  CuGeO$_3$

abstract:
  CuGeO$_3$ undergoes a transition from a spin-Peierls phase to an
incommensurate phase at a critical field of $H_c\approx 12.5$ T. In the
high-field phase a lattice of solitons forms, with both structural and magnetic
components, and these have been studied using neutron scattering techniques.
Our results provide direct evidence for a long-ranged magnetic soliton
structure which has both staggered and uniform magnetizations, and with
amplitudes that are broadly in accord with theoretical estimates. The magnetic
soliton width, $\Gamma$, and the field dependence of the incommensurability,
$\delta k_{sp}$, are found to agree well with theoretical predictions.


title:
Phase resolution limit in macroscopic interference between Bose-Einstein
  condensates

abstract:
  We study the competition between phase definition and quantum phase
fluctuations in interference experiments between independently formed Bose
condensates. While phase-sensitive detection of atoms makes the phase
progressively better defined, interactions tend to randomize it faster as the
uncertainty in the relative particle number grows. A steady state is reached
when the two effects cancel each other. Then the phase resolution saturates to
a value that grows with the ratio between the interaction strength and the atom
detection rate, and the average phase and number begin to fluctuate
classically. We discuss how our study applies to both recently performed and
possible future experiments.


title: Angle-dependent magnetothermal conductivity in d-wave superconductors

abstract:
  We analyse the behavior of the thermal conductivity, $\kappa(H)$, in the
vortex state of a quasi-two-dimensional d-wave superconductor when both the
heat current and the applied magnetic field are in the basal plane. At low
temperature the effect of the field is accounted for in a semiclassical
approximation, via a Doppler shift in the spectrum of the nodal quasiparticles.
In that regime $\kappa(H)$ exhibits twofold oscillations as a function of the
angle between the direction of the field in the plane and the direction of the
heat current, in agreement with experiment.


title: Thermal conductivity in the vortex state of d-wave superconductors

abstract:
  We present the results of a microscopic calculation of the longitudinal
thermal conductivity of quasiparticles, $\kappa_{xx}$, in a 2D d-wave
superconductor in the vortex state. Our approach takes into account both
impurity scattering and a contribution to the thermal transport lifetime due to
the scattering of quasiparticles off of vortices. We compare the results with
the experimental measurements on high-T$_c$ cuprates and organic
superconductors.


title: Universal Fluctuations in Correlated Systems

abstract:
  The probability density function (PDF) of a global measure in a large class
of highly correlated systems has been suggested to be of the same functional
form. Here, we identify the analytical form of the PDF of one such measure, the
order parameter in the low temperature phase of the 2D-XY model. We demonstrate
that this function describes the fluctuations of global quantities in other
correlated, equilibrium and non-equilibrium systems. These include a coupled
rotor model, Ising and percolation models, models of forest fires, sand-piles,
avalanches and granular media in a self organized critical state. We discuss
the relationship with both Gaussian and extremal statistics.


abstract:
  The Josephson-plasma and vortex modes in layered superconductors have been
studied theoretically for low magnetic fields parallel and perpendicular to
layers. The two modes belong to the same lowest-frequency branch of
collective-mode spectrum localized near vortices. This is the Josephson-plasma
resonance if pancakes are strongly pinned and cannot move. Otherwise the
lowest-frequency mode is a vortex mode governed by pancake pinning and the
vortex mass. The latter is strongly enhanced by wandering of a vortex line
around its average direction. The recently observed jump of the
magnetoabsorption-resonance frequency at the vortex phase transition line is
interpreted as a transition from the Josephson-plasma to the vortex mode.


title: Kinetic glass transition

abstract:
  Kinetic lattice-gas models display fragile glass behavior, in spite of their
trivial Gibbs-Boltzmann measure. This suggests that the nature of glass
transition might be, at least in some cases, understood in purely kinetic or
dynamical terms.


title:
Molecular dynamics simulation of the fragile glass former
  ortho-terphenyl: a flexible molecule model

abstract:
  We present a realistic model of the fragile glass former orthoterphenyl and
the results of extensive molecular dynamics simulations in which we
investigated its basic static and dynamic properties. In this model the
internal molecular interactions between the three rigid phenyl rings are
described by a set of force constants, including harmonic and anharmonic terms;
the interactions among different molecules are described by Lennard-Jones
site-site potentials. Self-diffusion properties are discussed in detail
together with the temperature and momentum dependencies of the
self-intermediate scattering function. The simulation data are compared with
existing experimental results and with the main predictions of the Mode
Coupling Theory.


title:
Giant AC magnetoresistance and anisotropic AC magnetoresistance in
  granular magnetic alloys

abstract:
  (withdrawn)AC resistance of melt-spun granular magnetic Cu85Co15 ribbons was
measured as a function of temperature in the range 5-300 K, magnetic field Hdc
in the range -60 kOe to 60 kOe, and frequency in the range 1-1000 Hz. A sharp
peak of zero-field resistance, which scales with frequency, and an associated
isotropic giant AC magnetoresistance in small fields are observed around the
temperature of collective freezing of interacting magnetic moments. Anomalous
behavior of AC resistance in large fields (Hdc > 20 kOe) is observed in a much
broader temperature range. This effect is not only frequency- dependent, but
also highly sensitive to anisotropy. We call it anisotropic AC
magnetoresistance.


title: Kink in a periodically modulated disordered system

abstract:
  We consider a dc-driven damped sine-Gordon model with a small nonlinear
spatial-disorder term, onto which a sinusoidal modulation is superimposed. It
describes, e.g., a weakly disordered system with a regular grain structure. We
demonstrate that, at the second order of the perturbation theory (with respect
to the weak spatial disorder), the periodically modulated disorder gives rise
to an effective periodic potential. Dynamics of a kink moving in this potential
is studied in the overdamped limit, using the adiabatic approximation, the main
objective being to consider depinning of a trapped kink. The analytical results
are compared with direct dynamical simulations of the underlying model, as well
as with numerical results using the collective-coordinate approach but without
the mean-field approximation. It is found that a critical force for the
depinning of a kink trapped by the periodically modulated weak spatial disorder
is much larger than that predicted by the mean-field approximation.


title: SO(5) Superconductors in a Zeeman Magnetic Field

abstract:
  The generic symmetry of a system under a uniform Zeeman magnetic field is
U(1) x U(1). However, we show that SO(5) models in the presence of a finite
chemical potential and a finite Zeeman magnetic field can have a exact SU(2) x
U(1) symmetry. This principle can be used to test SO(5) symmetry at any doping
level.


title: Persistent Current in Normal Metals

abstract:
  We discuss the recent experiments on persistent current in metallic rings in
the backdrop of low temperature decoherence. The observed size of the
persistent current, typically on the order of the Thouless energy, $ e/\tau_D$,
is much larger than the theoretical results, obtained with or without electron
interaction. In considering the phenomenology of both decoherence and
persistent current, usually observed in similar systems, we argue towards a
dynamic role played by decoherence in the generation of a persistent current. A
field-induced phase shift from near-equilibrium high-frequency
fluctuations---which otherwise gives rise to decoherence---under certain
conditions of periodicity and asymmetry due to disorder, is argued to induce a
steady state diffusion current on the order of $e/\tau_D$, comparable to the
observed persistent current.


title: Notes on Decoherence at Absolute Zero

abstract:
  The problem of electron decoherence at low temperature is analyzed from the
perspective of recent experiments on decoherence rate measurement and on
related localization phenomena in low-dimensional systems. Importance of
decoherence at zero temperature, perhaps induced by quantum fluctuations, is
put in a broader context.


title:
Universal Distributions for Growth Processes in 1+1 Dimensions and
  Random Matrices

abstract:
  We develop a scaling theory for KPZ growth in one dimension by a detailed
study of the polynuclear growth (PNG) model. In particular, we identify three
universal distributions for shape fluctuations and their dependence on the
macroscopic shape. These distribution functions are computed using the
partition function of Gaussian random matrices in a cosine potential.


title:
Anderson localization as a parametric instability of the linear kicked
  oscillator

abstract:
  We rigorously analyse the correspondence between the one-dimensional standard
Anderson model and a related classical system, the `kicked oscillator' with
noisy frequency. We show that the Anderson localization corresponds to a
parametric instability of the oscillator, with the localization length
determined by an increment of the exponential growth of the energy. Analytical
expression for a weak disorder is obtained, which is valid both inside the
energy band and at the band edge.


title:
Hall cross size scaling and its application to measurements on
  nanometer-size iron particle arrays

abstract:
  Hall crosses were used to measure the magnetic properties of arrays of
ferromagnetic, nanometer-scale iron particles. The arrays typically consist of
several hundred particles of 9 -- 20 nm in diameter. It is shown that the
sensitivity of the measurements can be improved by matching the areas of the
Hall cross and the array grown onto it by at least an order of magnitude. We
predict that single particles of diameter as small as 10 nm can be measured if
grown onto a Hall cross of appropriate size.


title: Vortex Flow and Transverse Flux Screening at the Bose Glass Transition

abstract:
  We investigate the vortex phase diagram in untwinned YBaCuO single crystals
with columnar defects. These randomly distributed defects, produced by heavy
ion irradiation, are expected to induce a ``Bose Glass'' phase of localized
vortices characterized by a vanishing resistance and a Meissner effect for
magnetic fields transverse to the defect axis. We directly observe the
transverse Meissner effect using an array of Hall probe magnetometers. As
predicted, the Meissner state breaks down at temperatures Ts that decrease
linearly with increasing transverse magnetic field. However, Ts falls well
below the conventional melting temperature Tm determined by a vanishing
resistivity, suggesting an intermediate regime where flux lines are effectively
localized even when rotated off the columnar defects.


title:
Vortex Creation in Bose-Einstein Condensates by Diffraction on a Helical
  Light Grating

abstract:
  It is shown that diffraction of Bose-Einstein condensates on a helical light
grating results in vortices in the condensate. Helical light gratings can be
produced by light interference of a Gaussian laser beam with a helical one.
Diffraction orders of the Bose-Einstein condensate contain vortices of
corresponding topological charge. The phenomena is illustrated by numerical
integration of the Gross-Pitaevskii equation in two dimensions.


title:
Spin and Charge Excitations in the Two-Dimensional t-J Model: Comparison
  with Fermi and Bose Systems

abstract:
  Using high temperature series we calculate temperature derivatives of the
spin-spin and density-density correlation functions to investigate the low
energy spin and charge excitations of the two-dimensional t-J model. We find
that the temperature derivatives indicate different momentum dependences for
the low energy spin and charge excitations. By comparing short distance
density-density correlation functions with those of spinless fermions and hard
core bosons, we find that the t-J model results are intermediate between the
two cases, being closer to those of hard core bosons. The implications of these
results for superconductivity are discussed.


title:
Confinement of Slave-Particles in U(1) Gauge Theories of
  Strongly-Interacting Electrons

abstract:
  We show that slave particles are always confined in U(1) gauge theories of
interacting electron systems. Consequently, the low-lying degrees of freedom
are different from the slave particles. This is done by constructing a dual
formulation of the slave-particle representation in which the no-double
occupany constraint becomes linear and, hence, soluble. Spin-charge separation,
if it occurs, is due to the existence of solitons with fractional quantum
numbers.


title: An Analytic Description of Light Emission in Sonoluminescence

abstract:
  Light emission in sonoluminescence is shown to be a lasing process with a
wide gain bandwidth. Population inversion of the gas molecules inside the
bubble is achieved by hydrodynamical pumping. Analytic expressions are derived
for the sonoluminescence pulse shape, pulse width, and their codependence on
the spectrum and intensity in physically relevant regimes. A detailed
comparison with experiments(R. Hiller et al., Phys. Rev. Lett. 80, 1090 (1998);
M.J. Moran et al., Phys. Rev. Lett. 80}, 4987 (1998); R. Pecha et al., Phys.
Rev. Lett. 81, 717 (1998)) suggests excellent agreement.


title: Exact Dynamics of the SU(K) Haldane-Shastry Model

abstract:
  The dynamical structure factor $S(q,\omega)$ of the SU(K) (K=2,3,4)
Haldane-Shastry model is derived exactly at zero temperature for arbitrary size
of the system. The result is interpreted in terms of free quasi-particles which
are generalization of spinons in the SU(2) case; the excited states relevant to
$S(q,\omega)$ consist of K quasi-particles each of which is characterized by a
set of K-1 quantum numbers. Near the boundaries of the region where
$S(q,\omega)$ is nonzero, $S(q,\omega)$ shows the power-law singularity. It is
found that the divergent singularity occurs only in the lowest edges starting
from $(q,\omega) = (0,0)$ toward positive and negative q. The analytic result
is checked numerically for finite systems via exact diagonalization and
recursion methods.

categories: cond-mat.str-el hep-th math.RT nlin.SI solv-int


title: Spin-1 chain doped with mobile S=1/2 fermions

abstract:
  We investigate doping of a two-orbital chain with mobile $S=1/2$ fermions as
a valid model for $\rm Y_{2-x}Ca_xBaNiO_5$. The S=1 spins are stabilized by
strong, ferromagnetic (fm) Hund's rule couplings. We calculate correlation
functions and thermodynamic quantities by DMRG methods and find a new hierarchy
of energy scales in the spin sector upon doping. Gapless spin-excitations are
generated at a lower energy scale by interactions among itinerant polarons
created by each hole and coexist with the larger scale of the gapful
spin-liquid background of the S=1 chain accompanied by a finite string-order
parameter.


title:
Vortex Creation in Bose-Einstein Condensates by Laser Beam Vortex
  Guiding

abstract:
  A technique for vortex creation in trapped Bose-Einstein condensates is
suggested: Vortices can be excited at the edge of a condensate and guided to
the center by a laser beam moving along a spiral trajectory. Numerical
simulations demonstrate the suggested technique. Parameter ranges for the
method are given. Computer animations illustrate the dynamics of the guided
vortices.


title: Two-dimensional random tilings of large codimension: new progress

abstract:
  Two-dimensional random tilings of rhombi can be seen as projections of
two-dimensional membranes embedded in hypercubic lattices of higher dimensional
spaces. Here, we consider tilings projected from a $D$-dimensional space. We
study the limiting case, when the quantity $D$, and therefore the number of
different species of tiles, become large. We had previously demonstrated [ICQ6]
that, in this limit, the thermodynamic properties of the tiling become
independent of the boundary conditions. The exact value of the limiting entropy
and finite $D$ corrections remain open questions. Here, we develop a mean-field
theory, which uses an iterative description of the tilings based on an analogy
with avoiding oriented walks on a random tiling. We compare the quantities
so-obtained with numerical calculations. We also discuss the role of spatial
correlations.