title:
Phase dependent differential thermopower of SND junctions: Pair-breaking
  effects and Gaussian fluctuations

abstract:
  We start with revisiting our previous results on thermoelectric response of
SNS configuration in a C-shaped Bi(x)Pb(1-x)Sr(2)CaCu(2)O(y) sample in order to
include strong fluctuation effects. Then, by appropriate generalization of the
Ginzburg-Landau theory based on admixture of s-wave and d-wave superconductors,
we consider a differential thermoelectric power (TEP) of SND junction. In
addition to its strong dependence on the relative phase \theta =\phi_s-\phi_d
between the two superconductors, two major effects are shown to influence the
behavior of the predicted TEP. One, based on the chemical imbalance at SD
interface, results in a pronounced maximum of the TEP peak near \theta =\pi /2
(where the so-called s+id mixed pairing state is formed) for two identical
superconductors (with T_d=T_s\equiv T_c). Another effect, which should manifest
itself at SD interface comprising an s-wave low-T_c superconductor and a d-wave
high-T_c superconductor (with T_d\neq T_s), predicts S_p\propto T_d-T_s for the
TEP peak value. The experimental conditions under which the predicted behavior
of the induced differential TEP can be measured are discussed.


title: Delocalization of tightly bound excitons in disordered systems

abstract:
  The localization length of a low energy tightly bound electron-hole pair
(excitons) is calculated by exact diagonalization for small interacting
disordered systems. The exciton localization length (which corresponds to the
thermal electronic conductance) is strongly enhanced by electron-electron
interactions, while the localization length (pertaining to the charge
conductance) is only slightly enhanced. This shows that the two particle
delocalization mechanism widely discussed for the electron pair case is more
efficient close to the Fermi energy for an electron-hole pair. The relevance to
experiment is also discussed.


title:
On the solutions of the one dimensional Ginzburg-Landau equations for
  superconductivity

abstract:
  This paper gives a complete description of the solutions of the one
dimensional Ginzburg-Landau equations which model superconductivity phenomena
in infinite slabs. We investigate this problem over the entire range of
physically important parameters: $a$ the size of the slab, $\kappa$ the
Ginzburg-Landau parameter, and $h_0$, the exterior magnetic field. We do
extensive numerical computations using the software AUTO, and determine the
number, symmetry and stability of solutions for all values of the parameters.
In particular, our experiments reveal the existence of two key-points in
parameter space which play a central role in the formation of the complicated
patterns by means of bifurcation phenomena. Our global description also allows
us to separate the various physically important regimes, to classify previous
results in each regime according to the values of the parameters and to derive
new open problems. In addition, our investigation provides new insight into the
problem of differentiating between the types of superconductors in terms of the
parameters.


title: Neutron Scattering from Magnetic Excitations in Bi_2 Sr_2 Ca_2 O_8+delta

abstract:
  Many physical properties of the copper oxide high temperature superconductors
appear to defy the conventional (one-electron) theory of metals, and the
development of new theories incorporating strong electron correlations is
currently at the forefront of condensed matter physics. Inelastic neutron
scattering provides incisive information about collective magnetic excitations
that is required to guide this effort. Such measurements have thus far proven
possible for only two of the many families of high temperature superconductors,
La_{2-x} Sr_x CuO_4 and YBa_2 Cu_3 O_{6+x},because suitably large single
crystals of other copper oxide compounds could not be grown. While the magnetic
spectra of both materials bear certain similarities, there are also pronounced
differences that have hampered a unified description of the spin dynamics in
the copper oxides. In particular, a sharp resonant spin excitation dominates
the spectrum in the superconducting state of YBa_2 Cu_3 O_{6+x}, but is not
found in La_{2-x} Sr_x CuO_4. Here we report the discovery of a magnetic
resonance peak in the superconducting state of a different copper oxide system,
Bi_2 Sr_2 Ca Cu_2 O_{8+\delta}, made possible by the synthesis of a sizable
single crystal and modern neutron optics. This provides evidence of the
generality of this unusual phenomenon among the copper oxides and greatly
extends the empirical basis for its theoretical description.


title: Heat Capacity Measurements in Pulsed Magnetic Fields

abstract:
  The new NHMFL 60T quasi-continuous magnet produces a flat-top field for a
period of 100 ms at 60 Tesla, and for longer time at lower fields, e.g. 0.5 sec
at 35 Tesla. We have developed for the first time the capability to measure
heat capacity at very high magnetic fields in the NHMFL 60 T quasi-continuous
magnet at LANL, using a probe built out of various plastic materials. The field
plateau allows us to utilize a heat-pulse method to obtain heat capacity data.
Proof-of-principle heat capacity experiments were performed on a variety of
correlated electron systems. Both magnet performance characteristics and
physical properties of various materials studied hold out a promise of wide
application of this new tool.


title:
Quasiparticle Density of States of Clean and Dirty s-Wave
  Superconductors in the Vortex State

abstract:
  The quasiparticle density of states (DOS) in the vortex state has been probed
by specific heat measurements under magnetic fields (H) for clean and dirty
s-wave superconductors, Y(Ni1-xPtx)2B2C and Nb1-xTaxSe2. We find that the
quasiparticle DOS per vortex is appreciably H-dependent in the clean-limit
superconductors, while it is H-independent in the dirty superconductors as
expected from a conventional rigid normal electron core picture. We discuss
possible origins for our observations in terms of the shrinking of the vortex
core radius with increasing H.


title:
Quasiparticle States near the Surface and the Domain Wall in a p_x\pm i
  p_y-Wave Superconductor

abstract:
  The electronic states near a surface or a domain wall in the p-wave
superconductor are studied for the order parameter of the form p_x\pm i
p_y-wave, which is a unitary odd-parity state with broken time-reversal
symmetry. This state has been recently suggested as the superconducting state
of Sr_2 Ru O_4. The spatial variation of the order parameter and vector
potential is determined self-consistently within the quasi-classical
approximation. The local density of states at the surface is constant and does
not show any peak-like or gap-like structure within the superconducting energy
gap, in contrast to the case of the d-wave superconductors. The influence of an
external magnetic field is mainly observable in the energy range above the bulk
gap. On the other hand, there is a small energy gap in the local density of
states at the domain wall between domains of the two degenerate p_x+i p_y-wave
and p_x-i p_y-wave states.


title:
Orbital Degree of Freedom and Phase Separation in Ferromagnetic
  Manganites at Finite Temperatures

abstract:
  The spin and orbital phase diagram for perovskite manganites are investigated
as a function of temperature and hole concentration. The superexchange and
double exchange interactions dominate the ferromagnetic phases in the low and
high concentration regions of doped holes, respectively.The two interactions
favor different orbital states each other. Between the phases, two interactions
compete with each other and the phase separation appears in the wide range of
temperature and hole concentration. The anisotropy of the orbital space causes
discontinuous changes of the orbital state and promotes the phase separation.
The relation between the phase separation and the stripe- and sheet-type charge
segregation is discussed.


title:
Absence of hysteresis at the Mott-Hubbard metal-insulator transition in
  infinite dimensions

abstract:
  The nature of the Mott-Hubbard metal-insulator transition in the
infinite-dimensional Hubbard model is investigated by Quantum Monte Carlo
simulations down to temperature T=W/140 (W=bandwidth). Calculating with
significantly higher precision than in previous work, we show that the
hysteresis below T_{IPT}\simeq 0.022W, reported in earlier studies, disappears.
Hence the transition is found to be continuous rather than discontinuous down
to at least T=0.325T_{IPT}. We also study the changes in the density of states
across the transition, which illustrate that the Fermi liquid breaks down
before the gap opens.


title: Reply to "Comment on Evidence for the droplet picture of spin glasses"

abstract:
  Using Monte Carlo simulations (MCS) and the Migdal-Kadanoff approximation
(MKA), Marinari et al. study in their comment on our paper the link overlap
between two replicas of a three-dimensional Ising spin glass in the presence of
a coupling between the replicas. They claim that the results of the MCS
indicate replica symmetry breaking (RSB), while those of the MKA are trivial,
and that moderate size lattices display the true low temperature behavior. Here
we show that these claims are incorrect, and that the results of MCS and MKA
both can be explained within the droplet picture.


title: Ground State and Excitations of Spin Chain with Orbital Degeneracy

abstract:
  The one dimensional Heisenberg model in the presence of orbital degeneracy is
studied at the SU(4) symmetric viewpoint by means of Bethe ansatz. Following
Sutherland's previous work on an equivalent model, we discuss the ground state
and the low-lying excitations more extensively in connection to the spin
systems with orbital degeneracy. We show explicitly that the ground state is a
SU(4) singlet. We study the degeneracies of the elementary excitations and the
spectra of the generalized magnons consisting of these excitations. We also
discuss the complex 2-strings in the context of the Bethe ansatz solutions.


title:
Anisotropic Superexchange for nearest and next nearest coppers in chain,
  ladder and lamellar cuprates

abstract:
  We present a detailed calculation of the magnetic couplings between
nearest-neighbor and next-nearest-neighbor coppers in the edge-sharing
geometry, ubiquitous in many cuprates. In this geometry, the interaction
between nearest neighbor coppers is mediated via two oxygens, and the Cu-O-Cu
angle is close to 90 degrees. The derivation is based on a perturbation
expansion of a general Hubbard Hamiltonian, and produces numerical estimates
for the various magnetic energies. In particular we find the dependence of the
anisotropy energies on the angular deviation away from the 90 degrees geometry
of the Cu-O-Cu bonds. Our results are required for the correct analysis of the
magnetic structure of various chain, ladder and lamellar cuprates.


title:
c-Axis Twist Bi2Sr2CaCu2O(8+delta) Josephson Junctions: A New
  Phase-Sensitive Test of Order Parmaeter Symmetry

abstract:
  Li et al. found that the critical current density JcJ across atomically clean
c-axis twist junctions of Bi2Sr2CaCu2O(8+x) is the same as that of the
constituent single crystal, JcS, independent of the twist angle phi0, even at
Tc. We investigated theoretically if a dx2-y2-wave order parameter might twist
by mixing in dxy components, but find that such twisting cannot possibly
explain the data near to Tc. Hence, the order parameter contains an s-wave
component, but not any dx2-y2-wave component. In addition, the c-axis Josephson
tunneling is completely incoherent. We also propose a c-axis junction
tricrystal experiment which does not rely upon expensive substrates.


title:
Soliton Lattices in the Incommensurate Spin-Peierls Phase: Local
  Distortions and Magnetizations

abstract:
  It is shown that nonadiabatic fluctuations of the soliton lattice in the
spin-Peierls system CuGeO_3 lead to an important reduction of the NMR line
widths. These fluctuations are the zero-point motion of the massless phasonic
excitations. Furthermore, we show that the discrepancy of X-ray and NMR soliton
widths can be understood as the difference between a distortive and a magnetic
width. Their ratio is controlled by the frustration of the spin system. By this
work, theoretical and experimental results can be reconciled in two important
points.


title: From semiconductors to superconductors: a simple model for pseudogaps

abstract:
  We consider a two dimensional semiconductor with a local attraction among the
carriers. We study the ground state of this system as a function of the
semiconductor gap. We find a direct transition from a superconducting to an
insulating phase for no doping at a critical value, the single particle
excitations being always gapped. For finite doping we find a smooth crossover.
We calculate the critical temperature due to both the particle excitations and
the Berezinkii-Kosterlitz-Thouless transition.


title: Structure Optimization and Frozen Phonons in LiNbO3

abstract:
  The equilibrium ground-state structure of LiNbO3 in the paraelectric and
ferroelectric phases is fully optimized in a first-principles calculation using
the full-potential linearized augmented plane wave method. The equilibrium
volume, c/a ratio and all (four, in the ferroelectric phase) internal
parameters are found to be in good agreement with the experimental data. Frozen
phonon calculations are performed for TO-Gamma phonons corresponding to the A1
and A2 irreducible representations of the R3c space group in the ferroelectric
phase. The comparison with available experimental frequencies for the A1 modes
is satisfactory (including the 6Li isotope effect), and the displacement
patterns are unambiguously attributed. For the (Raman inactive) A2 modes,
phonon frequencies and eigenvectors are predicted.


title:
Quantum Spinodal Decomposition in Multicomponent Bose-Einstein
  Condensates

abstract:
  We investigate analytically the non-equilibrium spatial phase segregation
process of a mixture of alkali Bose-Einstein condensates. Two stages (I and II)
are found in analogy to the classical spinodal decomposition.
  The coupled non-linear Schr\"odinger equations enable us to give a
quantitative picture of the present dynamical process in a square well trap.
  Both time and length scales in the stage I are obtained.
  We further propose that the stage II is dominated by the Josephson effect
between different domains of same condensate different from scenarios in the
classical spinodal decomposition.
  Its time scale is estimated.


title:
Combined study of KNbO3 and KTaO3 by different techniques of
  photoelectron and X-ray emission spectroscopy

abstract:
  The new results are presented of the experimental study of KNbO3 and KTaO3 by
means of X-ray photoelectron spectroscopy, soft X-ray emission and X-ray
fluorescence spectroscopy. In particular, Nb M(4,5) spectra have been measured
over a range of near-threshold excitation energies 206.5 - 240.6 eV, and Ta
N(3) spectra over 399.4 - 420.4 eV at the Advance Light Source in Berkeley.
These spectra were found to be strongly dependent on the excitation energy.
Moreover, the O K(alpha) X-ray emission spectra in both compounds as well as
the valence-band photoelectron spectra are brought to the binding energy scale
and discussed in combination. The trends in the spectra are explained on the
basis of first-principles band-structure calculations, with the dipole
transition matrix elements taken into account.


title: Improving the Efficiency of FP-LAPW Calculations

abstract:
  The full-potential linearized augmented-plane wave (FP-LAPW) method is well
known to enable most accurate calculations of the electronic structure and
magnetic properties of crystals and surfaces. The implementation of atomic
forces has greatly increased it's applicability, but it is still generally
believed that FP-LAPW calculations require substantial higher computational
effort compared to the pseudopotential plane wave (PPW) based methods.
  In the present paper we analyse the FP-LAPW method from a computational point
of view. Starting from an existing implementation (WIEN95 code), we identified
the time consuming parts and show how some of them can be formulated more
efficiently. In this context also the hardware architecture plays a crucial
role. The remaining computational effort is mainly determined by the setup and
diagonalization of the Hamiltonian matrix. For the latter, two different
iterative schemes are compared. The speed-up gained by these optimizations is
compared to the runtime of the ``original'' version of the code, and the PPW
approach. We expect that the strategies described here, can also be used to
speed up other computer codes, where similar tasks must be performed.


title:
Josephson Frequency Singularity in the Noise of Normal
  Metal-Superconductor Junctions

abstract:
  A singularity at the Josephson frequency in the noise spectral density of a
disordered normal metal -- superconductor junction is predicted for bias
voltages below the superconducting gap. The non-stationary Aharonov-Bohm
effect, recently introduced for normal metals, is proposed as a tool for
detecting this singularity. In the presence of a harmonic external field, the
derivative of the noise with respect to the voltage bias reveals jumps when the
applied frequency is commensurate with the Josephson frequency associated with
this bias. The height of these jumps is non-monotonic in the amplitude of the
periodic field. The superconducting flux quantum enters this dependence.
Additional singularities in the frequency dependent noise are predicted above
gap.


title:
A Two-dimensional Infinte System Density Matrix Renormalization Group
  Algorithm

abstract:
  It has proved difficult to extend the density matrix renormalization group
technique to large two-dimensional systems. In this Communication I present a
novel approach where the calculation is done directly in two dimensions. This
makes it possible to use an infinite system method, and for the first time the
fixed point in two dimensions is studied. By analyzing several related blocking
schemes I find that there exists an algorithm for which the local energy
decreases monotonically as the system size increases, thereby showing the
potential feasibility of this method.


title:
Evaluating the partition function for systems with long range
  interactions

abstract:
  We express the partition function for an equilibrium system of interacting
particles in the canonical ensemble as a functional integration over the
particles' density field. We outline a method to evaluate the partition
function by expanding around a saddle point. The saddle point is shown to be
the solution of the equivalent mean-field theory. Leading corrections to the
mean-field theory takes the form of a Gaussian integral.


title: Spin flop in one-dimensional quantum antiferromagnets

abstract:
  The field-induced transition corresponding to the spin flop in the quantum
antiferromagnetic chains in the presence of the Ising-like single-ion
anisotropy D (<0) is studied by the finite-cluster analysis. It is found that
for $S\geq {3\over 2}$ a first-order metamagnetic transition occurs even in one
dimension for small negative D except for the Haldane phase, while there exist
two second-order transitions and an incommensurate phase appears between them
for intermediate D, as already found for S=1. We also discuss on some
experiments of CsNiCl$_3$ related with the present work.


title: Force Distribution in a Granular Medium

abstract:
  We report on systematic measurements of the distribution of normal forces
exerted by granular material under uniaxial compression onto the interior
surfaces of a confining vessel. Our experiments on three-dimensional, random
packings of monodisperse glass beads show that this distribution is nearly
uniform for forces below the mean force and decays exponentially for forces
greater than the mean. The shape of the distribution and the value of the
exponential decay constant are unaffected by changes in the system preparation
history or in the boundary conditions. An empirical functional form for the
distribution is proposed that provides an excellent fit over the whole force
range measured and is also consistent with recent computer simulation data.


title:
Universal and non-universal properties of cross-correlations in
  financial time series

abstract:
  We use methods of random matrix theory to analyze the cross-correlation
matrix C of price changes of the largest 1000 US stocks for the 2-year period
1994-95. We find that the statistics of most of the eigenvalues in the spectrum
of C agree with the predictions of random matrix theory, but there are
deviations for a few of the largest eigenvalues. We find that C has the
universal properties of the Gaussian orthogonal ensemble of random matrices.
Furthermore, we analyze the eigenvectors of C through their inverse
participation ratio and find eigenvectors with large inverse participation
ratios at both edges of the eigenvalue spectrum--a situation reminiscent of
results in localization theory.


title: Electronic Transport in La-Ca Manganites

abstract:
  We revisit the transport properties of La-Ca manganites in detail, since they
have been confirmed in a number of CMR-exhibiting materials. We also discuss
new data considered the hallmark of an unusually high electron-phonon coupling
responsible for charge localization and small polaron transport.


title: Canonical BCS Approximation for the Attractive Hubbard Model

abstract:
  We test the canonical BCS wave functions for fixed number of electrons for
the attractive Hubbard model. We present results in one dimension for various
chain lengths, electron densities, and coupling strengths. The ground-state
energy and energy gap to the first excited state are compared with the exact
solutions obtained by the Bethe ansatz as well as with the results from the
conventional grand-canonical BCS approximations. While the canonical and
grand-canonical BCS results are both in very good agreement with the exact
results for the ground state energies, improvements due to conserving the
electron number in finite systems are manifest in the energy gap. As the system
size is increased, the canonical results converge to the grand-canonical ones.
The ``parity'' effect that arises from the number parity (even or odd) of
electrons are studied with our canonical scheme.


title: A Model for the Optical Absorption in Pororus Silicon

abstract:
  In this paper, we report on the optical absorption in porous silicon. We
model the absorption process assuming that porous silicon is a pseudo 1D
material system having a distribution of band gaps. We show that in order to
explain the absorption we specifically need to invoke - (a) k is not conserved
in optical transitions, (b) the oscillator strength of these transitions
depends on the size of the nanostructure in which absorption takes place and
(c) the distribution of band gaps significantly influences the optical
absorption. We also show that it is not possible to extract the band gap of
porous silicon from a plot of $\sqrt{\alpha\hbar\omega}$ vs $\hbar\omega$.


title: Pairing via Index theorem

abstract:
  This work is motivated by a specific point of view: at short distances and
high energies the undoped and underdoped cuprates resemble the $\pi$-flux phase
of the t-J model. The purpose of this paper is to present a mechanism by which
pairing grows out of the doped $\pi$-flux phase. According to this mechanism
pairing symmetry is determined by a parameter controlling the quantum tunneling
of gauge flux quanta. For zero tunneling the symmetry is $d_{x^2-y^2}+id_{xy}$,
while for large tunneling it is $d_{x^2-y^2}$. A zero-temperature critical
point separates these two limits.


title:
Relation between crystal and magnetic structures of the layered
  manganites La2-2xSr1+2xMn2O7 (0.30 =< x =< 0.50)

abstract:
  Comprehensive neutron-powder diffraction and Rietveld analyses were carried
out to clarify the relation between the crystal and magnetic structures of
La2-2xSr1+2xMn2O7 (0.30 =< x =< 0.50). The Jahn-Teller (JT) distortion of Mn-O6
octahedra, i.e., the ratio of the averaged apical Mn-O bond length to the
equatorial Mn-O bond length, is Delta_JT=1.042(5) at x=0.30, where the magnetic
easy-axis at low temperature is parallel to the c axis. As the JT distortion
becomes suppressed with increasing x, a planar ferromagnetic structure appears
at x =< 0.32, which is followed by a canted antiferromagnetic (AFM) structure
at x =< 0.39. The canting angle between neighboring planes continuously
increases from 0 deg (planar ferromagnet: 0.32 =< x < 0.39) to 180 deg (A-type
AFM: x=0.48 where Delta_JT=1.013(5)). Dominance of the A-type AF structure with
decrease of JT distortion can be ascribed to the change in the eg orbital state
from d3z^2-r^2 to dx^2-y^2.


title:
Numerical study of the strongly screened vortex glass model in an
  external field

abstract:
  The vortex glass model for a disordered high-T_c superconductor in an
external magnetic field is studied in the strong screening limit. With exact
ground state (i.e. T=0) calculations we show that 1) the ground state of the
vortex configuration varies drastically with infinitesimal variations of the
strength of the external field, 2) the minimum energy of global excitation
loops of length scale L do not depend on the strength of the external field,
however 3) the excitation loops themself depend sensibly on the field. From 2)
we infer the absence of a true superconducting state at any finite temperature
independent of the external field.


title:
Zero temperature metal-insulator transition in the infinite-dimensional
  Hubbard model

abstract:
  The zero temperature transition from a paramagnetic metal to a paramagnetic
insulator is investigated in the Dynamical Mean Field Theory for the Hubbard
model. The self-energy of the effective impurity Anderson model (on which the
Hubbard model is mapped) is calculated using Wilson's Numerical Renormalization
Group method. Results for quasiparticle weight, spectral function and
self-energy are discussed for Bethe and hypercubic lattice. In both cases, the
metal-insulator transition is found to occur via the vanishing of a
quasiparticle resonance which appears to be isolated from the Hubbard bands.


title: Epitaxial Growth Kinetics with Interacting Coherent Islands

abstract:
  The Stranski-Krastanov growth kinetics of undislocated (coherent)
3-dimensional islands is studied with a self-consistent mean field rate theory
that takes account of elastic interactions between the islands. The latter are
presumed to facilitate the detachment of atoms from the islands with a
consequent decrease in their average size. Semi-quantitative agreement with
experiment is found for the time evolution of the total island density and the
mean island size. When combined with scaling ideas, these results provide a
natural way to understand the often-observed initial increase and subsequent
decrease in the width of the coherent island size distribution.


title: The Fractional Quantum Hall Effect

abstract:
  We give a brief introduction to the phenomenon of the Fractional Quantum Hall
effect, whose discovery was awarded the Nobel prize in 1998. We also explain
the composite fermion picture which describes the fractional quantum Hall
effect as the integer quantum Hall effect of composite fermions.


title:
Quantum optics of a Bose-Einstein condensate coupled to a quantized
  light field

abstract:
  We consider the interaction between a Bose-Einstein condensate and a
single-mode quantized light field in the presence of a strong far off-resonant
pump laser. The dynamics is characterized by an exponential instability, hence
the system acts as an atom-photon parametric amplifier. Triggered by a small
injected probe field, or simply by quantum noise, entangled atom-photon pairs
are created which exhibit non-classical correlations similar to those seen
between photons in the optical parametric amplifier. In addition, the quantum
statistics of the matter and light fields depend strongly on the initial state
which triggers the amplifier. Thus by preparing different initial states of the
light field, one can generate matter waves in a variety of quantum states,
demonstrating optical control over the quantum statistics of matter waves.


title:
Why the lowest Landau level approximation works in strongly type II
  superconductors

abstract:
  Higher than the lowest Landau level contributions to magnetization and
specific heat of superconductors are calculated using Ginzburg - Landau
equations approach. Corrections to the excitation spectrum around solution of
these equations (treated perturbatively) are found. Due to symmetries of the
problem leading to numerous cancellations the range of validity of the LLL
approximation in mean field is much wider then a naive range and extends all
the way down to $H = {H_{c2}(T)}/13$. Moreover the contribution of higher
Landau levels is significantly smaller compared to LLL than expected naively.
We show that like the LLL part the lattice excitation spectrum at small
quasimomenta is softer than that of usual acoustic phonons. This enhanses the
effect of fluctuations. The mean field calculation extends to third order,
while the fluctuation contribution due to HLL is to one loop. This complements
the earlier calculation of the LLL part to two loop order.


title:
Height representation, critical exponents, and ergodicity in the
  four-state triangular Potts antiferromagnet

abstract:
  We study the four-state antiferromagnetic Potts model on the triangular
lattice. We show that the model has six types of defects which diffuse and
annihilate according to certain conservation laws consistent with their having
a vector-valued topological charge. Using the properties of these defects, we
deduce a 2+2-dimensional height representation for the model and hence show
that the model is equivalent to the three-state Potts antiferromagnet on the
Kagome lattice and to bond-coloring models on the triangular and hexagonal
lattices. We also calculate critical exponents for the ground state ensemble of
the model. We find that the exponents governing the spin-spin correlation
function and spin fluctuations violate the Fisher scaling law because of
constraints on path length which increase the effective wavelength of the spin
operator on the height lattice. We confirm our predictions by extensive Monte
Carlo simulations of the model using the Wang-Swendsen-Kotecky cluster
algorithm. Although this algorithm is not ergodic on lattices with toroidal
boundary conditions, we prove that it is ergodic on lattices with free boundary
conditions, or more generally on lattices possessing no non-contractible loops
of infinite order. To guard against biases introduced by lack of ergodicity, we
therefore perform our simulations on both the torus and the projective plane.


title:
Commuting quantum transfer matrix approach to intrinsic Fermion system:
  Correlation length of a spinless Fermion model

abstract:
  The quantum transfer matrix (QTM) approach to integrable lattice Fermion
systems is presented. As a simple case we treat the spinless Fermion model with
repulsive interaction in critical regime. We derive a set of non-linear
integral equations which characterize the free energy and the correlation
length of $<c_j^{\dagger}c_i>$ for arbitrary particle density at any finite
temperatures. The correlation length is determined by solving the integral
equations numerically. Especially in low temperature limit this result agrees
with the prediction from conformal field theory (CFT) with high accuracy.

categories: cond-mat.stat-mech hep-th math-ph math.MP math.QA nlin.SI solv-int


title:
1D Quantum transport in the even-chain spin-ladder compound
  Sr2.5Ca11.5Cu24O41 and YBa2Cu4O8

abstract:
  The temperature dependence of the resistivity r(T) of the novel
Sr2.5Ca11.5Cu24O41 ladder compound under hydrostatic pressure of up to 8 GPa
has been explained by assuming that the relevant length scale for electrical
transport is given by the magnetic correlation length related to the opening of
a spin-gap in a 1D even-chain spin-ladder (1D-SL). The pressure dependence of
the gap was extracted by applying this model to r(T) data obtained at different
pressures. The r(T) dependence of the underdoped cuprate YBa2Cu4O8 demonstrates
a remarkable scaling with the r(T) of the 1D-SL compound Sr2.5Ca11.5Cu24O41.
This scaling implies that underdoped cuprates at Tc < T < T* are in the 1D
regime and their pseudo-gap below T* is the spin-gap in the even-chain 1D-SL
formed at T < T* in these materials.


title:
La substitution induced linear temperature dependence of electrical
  resistivity and Kondo behavior in the alloys, Ce_{2-x}La_{x}CoSi_{3}

abstract:
  The results of electrical resistivity, heat capacity and magnetic
susceptibility behavior of new class of alloys, Ce_{2-x}La_{x}CoSi_{3}, are
reported. The x= 0.0 alloy is mixed valent and La substitution for Ce (x= 0.25)
induces linear temperature dependence of resistivity at low temperatures, an
observation of relevance to the topic of non-Fermi liquid behavior. The
modifications of Kondo effect for all the alloys are also presented.


title:
Hall-effect in LuNi_2B_2C and YNi_2B_2C borocarbides: a comparative
  study

abstract:
  The Hall effect in LuNi_2B_2C and YNi_2B_2C borocarbides has been
investigated in normal and superconducting mixed states. The Hall resistivity
rho_{xy} for both compounds is negative in the normal as well as in the mixed
state and has no sign reversal below T_c typical for high-T_c superconductors.
In the mixed state the behavior of both systems is quite similar. The scaling
relation rho_{xy}\sim\rho_{xx}^\beta (\rho_{xx} is the longitudinal
resistivity) was found with \beta=2.0 and 2.1 for annealed Lu- and Y-based
compounds, respectively. The scaling exponent \beta decreases with increasing
degree of disorder and can be varied by annealing. This is attributed to a
variation of the strength of flux pinning. In the normal state weakly
temperature dependent Hall coefficients were observed for both compounds. A
distinct nonlinearity in the \rho_{xy} dependence on field H was found for
LuNi_2B_2C in the normal state below 40K, accompanied by a large
magnetoresistance (MR) reaching +90% for H=160kOe at T=20K. At the same time
for YNi_2B_2C only linear \rho_{xy}(H) dependences were observed in the normal
state with an approximately three times lower MR value. This difference in the
normal state behavior of the very similar Lu- and Y-based borocarbides seems to
be connected with the difference in the topology of the Fermi surface of these
compounds.


abstract:
  We investigate Monte Carlo energy and variance minimization techniques for
optimizing many-body wave functions. Several variants of the basic techniques
are studied, including limiting the variations in the weighting factors which
arise in correlated sampling estimations of the energy and its variance. We
investigate the numerical stability of the techniques and identify two reasons
why variance minimization exhibits superior numerical stability to energy
minimization. The characteristics of each method are studied using a
non-interacting 64-electron model of crystalline silicon. While our main
interest is in solid state systems, the issues investigated are relevant to
Monte Carlo studies of atoms, molecules and solids. We identify a robust and
efficient variance minimization scheme for optimizing wave functions for large
systems.


title: Quantum tunneling across spin domains in a Bose-Einstein condensate

abstract:
  Quantum tunneling was observed in the decay of metastable spin domains in
gaseous Bose-Einstein condensates. A mean-field description of the tunneling
was developed and compared with measurement. The tunneling rates are a
sensitive probe of the boundary between spin domains, and indicate a spin
structure in the boundary between spin domains which is prohibited in the bulk
fluid. These experiments were performed with optically trapped F=1 spinor
Bose-Einstein condensates of sodium.


title:
Evidence for vortex staircases in the whole angular range due to
  competing correlated pinning mechanisms

abstract:
  We analyze the angular dependence of the irreversible magnetization of
YBa$_2$Cu$_3$O$_7$ crystals with columnar defects inclined from the c-axis. At
high fields a sharp maximum centered at the tracks' direction is observed. At
low fields we identify a lock-in phase characterized by an angle-independent
pinning strength and observe an angular shift of the peak towards the c-axis
that originates in the material anisotropy. The interplay among columnar
defects, twins and ab-planes generates a variety of staircase structures. We
show that correlated pinning dominates for all field orientations.


title: Broken Symmetries in Scanning Tunneling Images of Carbon Nanotubes

abstract:
  Scanning tunneling images of carbon nanotubes frequently show electron
distributions which break the local sixfold symmetry of the graphene sheet. We
present a theory of these images which relates these anisotropies to the off
diagonal correlations in the single particle density matrix, and allows one to
extract these correlations from the observed images. The theory is applied to
images of the low energy states reflected at the end of a tube or by point
defects, and to states propagating on defect free semiconducting tubes. The
latter exhibit a novel switching of the anisotropy in the tunneling image with
the sign of the tunneling bias.


title: Reweighting in nonequilibrium simulations

abstract:
  A simple reweighting scheme is proposed for Monte Carlo simulations of
interacting particle systems, permitting one to study various parameter values
in a single study, and improving efficiency by an order of magnitude. Unlike
earlier reweighting schemes, the present approach does not require knowledge of
the stationary probability distribution, and so is applicable out of
equilibrium. The method is applied to the contact process in two and three
dimensions, yielding the critical parameter and spreading exponents to
unprecedented precision.


title: Mean-field theory of strongly disordered superconductors

abstract:
  Qualitative features of the mean-field theory of superconductivity in a
strongly disordered systems of fermions with short-range attraction are
discussed. In this limit the effective theory is entirely bosonic, and I
consider both the artificial infinite-range limit, and the more realistic case
of "nearest neighbor" hopping of bosons between localized states. In the
infinite range case the mean-field theory is exact, and the superconducting gap
is uniform in space. There is a smooth BCS-BEC crossover with decrease in
density, at weak enough disorder; at moderate densities, or larger disorder,
the mean-field ground state is the BCS-like localized superconductor. In the
latter case, the gap is highly non-uniform in space, but surprisingly stays
everywhere finite below the mean-field transition temperature.


title: Nonlinear voltage dependence of shot noise

abstract:
  The current noise in a multi-probe mesoscopic conductor can have a nonlinear
dependence on the strength of driving bias voltage. This paper presents a
theoretical formulation for the nonlinear noise spectra. We pay special
attention to maintain gauge invariance at the nonlinear level. At small but
finite voltages, explicit expressions for nonlinear noise spectra, expanded
order by order in the bias, have been derived. In the wideband limit, a closed
form solution of the noise spectra for finite voltages is obtained.


title: Nonlinear I-V Characteristics of a Mesoscopic Conductor

abstract:
  We present a general theoretical formulation, based on nonequilibrium Green's
functions, for nonlinear DC transport in multi-probe mesoscopic conductors. The
theory is gauge invariant and is useful for the predictions of current-voltage
characteristics and the nonequilibrium charge pile-ups inside the conductor. We
have provided a detailed comparison between the gauge invariant scattering
matrix theory and our theory. We have also given several examples where the I-V
curve can be obtained analytically. The effects of exchange and correlation
have been considered explicitly.


title: On the existence of a Bose Metal at T=0

abstract:
  This paper aims to justify, at a microscopic level, the existence of a
two-dimensional Bose metal, i.e. a metallic phase made out of Cooper pairs at
T=0. To this end, we consider the physics of quantum phase fluctuations in
(granular) superconductors in the absence of disorder and emphasise the role of
two order parameters in the problem, viz. phase order and charge order. We
focus on the 2-d Bose Hubbard model in the limit of very large fillings, i.e. a
2-d array of Josephson junctions. We find that the algebra of phase
fluctuations is that of the Euclidean group $E_{2}$ in this limit, and show
that the model is equivalent to two coupled XY models in (2+1)-d, one
corresponding to the phase degrees of freedom, and the other the charge degrees
of freedom. The Bose metal, then, is the phase in which both these degrees of
freedom are disordered(as a result of quantum frustration). We analyse the
model in terms of its topological excitations and suggest that there is a
strong indication that this state represents a surface of critical points, akin
to the gapless spin liquid states. We find a remarkable consistency of this
scenario with certain low-T_c thin film experiments.

categories: cond-mat.supr-con cond-mat.dis-nn cond-mat.mes-hall cond-mat.mtrl-sci cond-mat.stat-mech cond-mat.str-el


title: Nonlinear Quantum Capacitance

abstract:
  We analyze the nonlinear voltage dependence of elelctrochemical capacitance
for nano-scale conductors. This voltage dependence is due to finite density of
states of the conductors. We derive an exact expression for the electrochemical
capacitance-voltage curve for a parallel plate system. The result suggests a
quantum scanning capacitance microscopy at the nano-scale: by inverting the
capacitance-voltage expression one is able to deduce the local spectral
function of the nano-scale conductor.


title: The Role of the Carrier Mass in Semiconductor Quantum Dots

abstract:
  In the present work we undertake a re-examination of effective mass theory
(EMT) for a semiconductor quantum dot. We take into account the fact that the
effective mass ($m_i$) of the carrier inside the dot of radius R is distinct
from the mass ($m_o$) in the dielectric coating surrounding the dot. The
electronic structure of the quantum dot is determined in crucial ways by the
mass discontinuity factor $\beta \equiv m_i/m_o$. In this connection we propose
a novel quantum scale, $\sigma$, which is a dimensionless parameter
proportional to $\beta^2 V_0 R^2$, where $V_0$ represents the barrier due to
dielectric coating. The scale $\sigma$ represents a mass modified ``strength''
of the potential. We show both by numerical calculations and asymptotic
analysis that the charge density near the nanocrystallite surface, $\rho (r =
R)$, can be large and scales as $1/\sigma$. This fact suggests a significant
role for the surface in an EMT based model. We also show that the upshift in
the ground state energy is weaker than quadratic, unlike traditional EMT based
calculations, and chart its dependence on the proposed scale $\sigma$. Finally,
we demonstrate that calculations based on our model compare favorably with
valence band photoemission data and with more elaborate theoretical
calculations.


title:
Transition from Haldane Phase to Spin Liquid and Incommensurate
  Correlation in Spin-1/2 Heisenberg Chains

abstract:
  The bulk properties and impurity effect in the one-dimensional S=1/2
Heisenberg model with dimerization and next-nearest-neighbor exchange are
studied by the density matrix renormalization group (DMRG) and exact
diagonalization methods. This model widely covers the S=1 Heisenberg model,
two-leg ladders, bond-alternating chains and the S=1/2 Heisenberg model. Almost
the whole parameter space belongs to the Haldane phase. In the non-dimerizing
limit a transition to a kind of spin liquid takes place, characterized by the
delocalized spin polarization. This transition causes the distinct impurity
effects between a spin-Peierls compound CuGeO_{3} and the Haldane systems.
Experimental aspects of a bond-alternating compound CuNb_{2}O_{6} are also
discussed. Furthermore, the incommensurate correlation arising in this model is
extensively studied, and a phase diagram is constructed.


title: Statistical mechanics of image restoration and error-correcting codes

abstract:
  We develop a statistical-mechanical formulation for image restoration and
error-correcting codes. These problems are shown to be equivalent to the Ising
spin glass with ferromagnetic bias under random external fields. We prove that
the quality of restoration/decoding is maximized at a specific set of parameter
values determined by the source and channel properties. For image restoration
in mean-field system a line of optimal performance is shown to exist in the
parameter space. These results are illustrated by solving exactly the
infinite-range model. The solutions enable us to determine how precisely one
should estimate unknown parameters. Monte Carlo simulations are carried out to
see how far the conclusions from the infinite-range model are applicable to the
more realistic two-dimensional case in image restoration.


title:
Temperature suppression of STM-induced desorption of hydrogen on Si(100)
  surfaces

abstract:
  The temperature dependence of hydrogen (H) desorption from Si(100)
H-terminated surfaces by a scanning tunneling microscope (STM) is reported for
negative sample bias. It is found that the STM induced H desorption rate ($R$)
decreases several orders of magnitude when the substrate temperature is
increased from 300 K to 610 K. This is most noticeable at a bias voltage of -7
V where $R$ decreases by a factor of ~200 for a temperature change of 80 K,
whilst it only decreases by a factor of ~3 at -5 V upon the same temperature
change. The experimental data can be explained by desorption due to vibrational
heating by inelastic scattering via a hole resonance. This theory predicts a
weak suppression of desorption with increasing temperature due to a decreasing
vibrational lifetime, and a strong bias dependent suppression due to a
temperature dependent lifetime of the hole resonance.


title: Correlations of Eigenvectors for Non-Hermitian Random-Matrix Models

abstract:
  We establish a general relation between the diagonal correlator of
eigenvectors and the spectral Green's function for non-hermitian random-matrix
models in the large-N limit. We apply this result to a number of non-hermitian
random-matrix models and show that the outcome is in good agreement with
numerical results.

categories: cond-mat chao-dyn hep-ph nlin.CD nucl-th


title: Theory of suppressed shot-noise at $\nu=2/(2p+\chi)$

abstract:
  We study the edge states of fractional quantum Hall liquid at bulk filling
factor $\nu=2/(2p+\chi)$ with $p$ being an even integer and $\chi=\pm 1$. We
describe the transition from a conductance plateau $G=\nu G_0=\nu e^2/h$ to
another plateau $G=G_0/(p+\chi)$ in terms of chiral Tomonaga-Luttinger liquid
theory. It is found that the fractional charge $q$ which appears in the
classical shot-noise formula $S_{I}=2q <I_b>$ is $q=e/(2p+\chi)$ on the
conductance plateau at $G=\nu G_0$ whereas on the plateau at $G=G_0/(p+\chi)$
it is given by $q=e/(p+\chi)$. For $p=2$ and $\chi=-1$ an alternative hierarchy
constructions is also discussed to explain the suppressed shot-noise experiment
at bulk filling factor $\nu=2/3$.


title: Hydrodynamic theory of an electron gas

abstract:
  The generalised hydrodynamic theory of an electron gas, which does not rely
on an assumption of a local equilibrium, is derived as the long-wave limit of a
kinetic equation. Apart from the common hydrodynamics variables the theory
includes the tensor fields of the higher moments of the distribution function.
In contrast to the Bloch hydrodynamics, the theory leads to the correct plasmon
dispersion and in the low frequency limit recovers the Navies-Stocks
hydrodynamics. The linear approximation to the generalised hydrodynamics is
closely related to the theory of highly viscous fluids.


title:
Small polaron formation in many-particle states of the Hubbard-Holstein
  model: The one-dimensional case

abstract:
  We investigate polaron formation in a many-electron system in the presence of
a local repulsion sufficiently strong to prevent local-bipolaron formation.
Specifically, we consider a Hubbard-Holstein model of interacting electrons
coupled to dispersionless phonons of frequency $\omega_0$. Numerically solving
the model in a small one-dimensional cluster, we find that in the nearly
adiabatic case $\omega_0 < t$, the necessary and sufficient condition for the
polaronic regime to occur is that the energy gain in the atomic (i.e.,
extremely localized) regime ${\cal E}_{pol}$ overcomes the energy of the purely
electronic system $ {\cal E}_{el}$. In the antiadiabatic case, $\omega_0 > t$,
polaron formation is instead driven by the condition of a large ionic
displacement $g/\omega_0 >1$ ($g$ being the electron-phonon coupling).
Dynamical properties of the model in the weak and moderately strong coupling
regimes are also analyzed.


title:
Scaling of broadband dielectric data of glass-forming liquids and
  plastic crystals

abstract:
  The Nagel-scaling and the modified scaling procedure proposed recently by
Dendzik et al. have been applied to broadband dielectric data on two glass-
forming liquids (glycerol and propylene carbonate) and three plastic crystals
(ortho-carborane, meta-carborane, and 1-cyano-adamantane). Our data extend the
upper limit of the abscissa range to considerably higher values than in
previously published analyses. At the highest frequencies investigated,
deviations from a single master curve show up which are most pronounced in the
Dendzik-scaling plot. The loss curves of the plastic crystals do not scale in
the Nagel-plot, but they fall onto a separate master curve in the Dendzik-plot.
In addition, we address the question of a possible divergence of the static
susceptibility near the Vogel-Fulcher temperature. For this purpose, the
low-temperature evolution of the high-frequency wing of the dielectric loss
peaks is investigated in detail. No convincing proof for such a divergence can
be deduced from the present broadband data.


title:
Neutron Scattering Study of Elastic Magnetic Signals in Superconducting
  La1.94Sr0.06Cu4

abstract:
  Recent neutron-scattering experiments on La(2-x)Sr(x)CuO4 single crystals by
Wakimoto et al. have revealed that elastic magnetic peaks appear at low
temperatures in both insulating (x=0.02-0.05) and superconducting (x=0.06)
samples. We have carried out further investigations particularly on the elastic
incommensurate peaks for x=0.06, and found that the integrated intensity
drastically changes across the low temperature insulator- superconductor
boundary; the intensity of x=0.06 is 4 times smaller than that of x=0.05, while
the intensity in the insulating region stays constant.


title: Charge Relaxation and Dephasing in Coulomb Coupled Conductors

abstract:
  The dephasing time in coupled mesoscopic conductors is caused by the
fluctuations of the dipolar charge permitted by the long range Coulomb
interaction. We relate the phase breaking time to elementary transport
coefficients which describe the dynamics of this dipole: the capacitance, an
equilibrium charge relaxation resistance and in the presence of transport
through one of the conductors a non-equilibrium charge relaxation resistance.
The discussion is illustrated for a quantum point contact in a high magnetic
field in proximity to a quantum dot.


title: Critical quantum chaos and the one dimensional Harper model

abstract:
  We study the quasiperiodic Harper's model in order to give further support
for a possible universality of the critical spectral statistics. At the
mobility edge we numerically obtain a scale-invariant distribution of the bands
$S$, which is closely described by a semi-Poisson $P(S)=4S \exp(-2S)$ curve.
The $\exp (-2S)$ tail appears when the mobility edge is approached from the
metal while $P(S)$ is asymptotically log-normal for the insulator. The
multifractal critical density of states also leads to a sub-Poisson linear
number variance $\Sigma_{2}(E)\propto 0.041E$.


title:
Crystallization of a classical two-dimensional electron system:
  Positional and orientational orders

abstract:
  Crystallization of a classical two-dimensional one-component plasma
(electrons interacting with the Coulomb repulsion in a uniform neutralizing
positive background) is investigated with a molecular dynamics simulation. The
positional and the orientational correlation functions are calculated for the
first time. We have found an indication that the solid phase has a
quasi-long-range (power-law) positional order along with a long-range
orientational order. This indicates that, although the long-range Coulomb
interaction is outside the scope of Mermin's theorem, the absence of ordinary
crystalline order at finite temperatures applies to the electron system as
well. The `hexatic' phase, which is predicted between the liquid and the solid
phases by the Kosterlitz-Thouless-Halperin-Nelson-Young theory, is also
discussed.


title:
Critical Currents, Pinning Forces and Irreversibility Fields in
  (YxTml-x)Ba2Cu3O7 Single Crystals with Columnar Defects in Fields up to 50 T

abstract:
  We have studied the influence of columnar defects, created by heavy-ion (Kr)
irradiation with doses up to 6 10^11 Kr-ions/cm2, on the superconducting
critical parameters of single crystalline (YxTm1-x)Ba2Cu3O7. Magnetisation
measurements in pulsed fields up to 50 T in the temperature range 4.2 - 90 K
revealed that: (i) in fields up to T the critical current Jc(H,T) is
considerably enhanced and (ii) down to temperatures T ~ 40 K the
irreversibility field Hirr(T) is strongly increased. The field range and
magnitude of the Jc(H,T) and Hirr(T) enhancement increase with increasing
irradiation dose. To interpret these observations, an effective matching field
was defined. Moreover, introducing columnar defects also changes the pinning
force fp qualitatively. Due to stronger pinning of flux lines by the amorphous
defects, the superconducting critical parameters largely exceed those
associated with the defect structures in the unirradiated as-grown material:
Jc,irrad(77 K, 5 T) ^3 10* Jc,ref(77 K, 5 T).


title: Optical response of superfluid state in dilute atomic Fermi-Dirac gases

abstract:
  We theoretically study the propagation of light in a Fermi-Dirac gas in the
presence of a superfluid state. BCS pairing between atoms in different
hyperfine levels may significantly increase the optical linewidth and line
shift of a quantum degenerate Fermi-Dirac gas and introduce a local-field
correction that, under certain conditions, dramatically dominates over the
Lorentz-Lorenz shift. These optical properties could possibly unambiguously
sign the presence of the superfluid state and determine the value of the BCS
order parameter.


title:
Statistical Mechanics of Charged Polymers in Electrolyte Solutions: A
  Lattice Field Theory Approach

abstract:
  The lattice field theory approach to the statistical mechanics of a classical
Coulomb gas [R. Coalson and A. Duncan, J. Chem. Phys. 97,5653(1992)] is
generalized to include charged polymer chains. Saddle-point analysis is done on
the functional integral representing the partition function of the full system.
Mean-field level analysis requires extremization of a real-valued functional
with a single minimum, thus guaranteeing a unique solution. The full mean-field
equations for such a coupled system are derived, as well as the leading
(one-loop) fluctuation corrections. Two different numerical real-space lattice
procedures are developed to implement the generalized theory; these are applied
to the problem of a charged polymer confined to a spherical cavity in an
electrolyte solution. The results provide new insight into the physics of
confined polyelectrolytes.


title:
High temperature study of the Kosterlitz-Thouless phase transition in
  the XY model on the triangular lattice

abstract:
  High temperature series expansions of the spin-spin correlation function for
the XY (or plane rotator) model on the triangular lattice are extended by two
terms up to order beta^{14}. Tables of the expansion coefficients are reported
for the correlation function spherical moments of order l=0 and 2. Our analysis
of the series supports the Kosterlitz-Thouless predictions on the structure of
the critical singularities and leads to fairly accurate estimates of the
critical parameters.


title:
Remnant Fermi surface in the presence of an underlying instability in
  layered 1T-TaS_2

abstract:
  We report high resolution angle-scanned photoemission and Fermi surface (FS)
mapping experiments on the layered transition-metal dichalcogenide 1T-TaS_2 in
the quasi commensurate (QC) and the commensurate (C) charge-density-wave (CDW)
phase. Instead of a nesting induced partially removed FS in the CDW phase we
find a pseudogap over large portions of the FS. This remnant FS exhibits the
symmetry of the one-particle normal state FS even when passing from the
QC-phase to the C-phase. Possibly, this Mott localization induced transition
represents the underlying instability responsible for the pseudogapped FS.


title: Can the trace formula describe weak localisation?

abstract:
  We attempt to systematically derive perturbative quantum corrections to the
Berry diagonal approximation of the two-level correlation function (TLCF) for
chaotic systems. To this end, we develop a ``weak diagonal approximation''
based on a recent description of the first weak localisation correction to
conductance in terms of the Gutzwiller trace formula. This semiclassical method
is tested by using it to derive the weak localisation corrections to the TLCF
for a semiclassically disordered system. Unfortunately the method is unable to
correctly reproduce the ``Hikami boxes'' (the relatively small regions where
classical paths are glued together by quantum processes). This results in the
method failing to reproduce the well known weak localisation expansion. It so
happens that for the first order correction it merely produces the wrong
prefactor. However for the second order correction, it is unable to reproduce
certain contributions, and leads to a result which is of a different form to
the standard one.


title:
Ground State Spin Oscillations of a Two-Electron Quantum Dot in a
  Magnetic Field

abstract:
  Crossings between spin-singlet and spin-triplet lowest states are analyzed
within the model of a two-electron quantum dot in a perpendicular magnetic
field. The explicit expressions in terms of the magnetic field, the magnetic
quantum number $m$ of the state and the dimensionless dot size for these
crossings are found.


title: Mobility of Bloch Walls via the Collective Coordinate Method

abstract:
  We have studied the problem of the dissipative motion of Bloch walls
considering a totally anisotropic one dimensional spin chain in the presence of
a magnetic field. Using the so-called "collective coordinate method" we
construct an effective Hamiltonian for the Bloch wall coupled to the magnetic
excitations of the system. It allows us to analyze the Brownian motion of the
wall in terms of the reflection coefficient of the effective potential felt by
the excitations due to the existence of the wall. We find that for finite
values of the external field the wall mobility is also finite. The spectrum of
the potential at large fields is investigated and the dependence of the damping
constant on temperature is evaluated. As a result we find the temperature and
magnetic field dependence of the wall mobility.


title: Dynamical Scaling: the Two-Dimensional XY Model Following a Quench

abstract:
  To sensitively test scaling in the 2D XY model quenched from
high-temperatures into the ordered phase, we study the difference between
measured correlations and the (scaling) results of a Gaussian-closure
approximation. We also directly compare various length-scales. All of our
results are consistent with dynamical scaling and an asymptotic growth law $L
\sim (t/\ln[t/t_0])^{1/2}$, though with a time-scale $t_0$ that depends on the
length-scale in question. We then reconstruct correlations from the
minimal-energy configuration consistent with the vortex positions, and find
them significantly different from the ``natural'' correlations --- though both
scale with $L$. This indicates that both topological (vortex) and
non-topological (``spin-wave'') contributions to correlations are relevant
arbitrarily late after the quench. We also present a consistent definition of
dynamical scaling applicable more generally, and emphasize how to generalize
our approach to other quenched systems where dynamical scaling is in question.
Our approach directly applies to planar liquid-crystal systems.


title:
Nucleus-Electron Model for States Changing from a Liquid Metal to a
  Plasma and the Saha Equation

abstract:
  We extend the quantal hypernetted-chain (QHNC) method, which has been proved
to yield accurate results for liquid metals, to treat a partially ionized
plasma. In a plasma, the electrons change from a quantum to a classical fluid
gradually with increasing temperature; the QHNC method applied to the electron
gas is in fact able to provide the electron-electron correlation at arbitrary
temperature. As an illustrating example of this approach, we investigate how
liquid rubidium becomes a plasma by increasing the temperature from 0 to 30 eV
at a fixed normal ion-density $1.03 \times 10^{22}/cm^3$. The electron-ion
radial distribution function (RDF) in liquid Rb has distinct inner-core and
outer-core parts. Even at a temperature of 1 eV, this clear distinction remains
as a characteristic of a liquid metal. At a temperature of 3 eV, this
distinction disappears, and rubidium becomes a plasma with the ionization 1.21.
The temperature variations of bound levels in each ion and the average
ionization are calculated in Rb plasmas at the same time. Using the
density-functional theory, we also derive the Saha equation applicable even to
a high-density plasma at low temperatures. The QHNC method provides a procedure
to solve this Saha equation with ease by using a recursive formula; the charge
population of differently ionized species are obtained in Rb plasmas at several
temperatures. In this way, it is shown that, with the atomic number as the only
input, the QHNC method produces the average ionization, the electron-ion and
ion-ion RDF's, and the charge population which are consistent with the atomic
structure of each ion for a partially ionized plasma.


title: Microscopic theory of vortex dynamics in homogeneous superconductors

abstract:
  Vortex dynamics in fermionic superfluids is carefully considered from the
microscopic point of view. Finite temperatures, as well as impurities, are
explicitly incorporated. To enable readers understand the physical
implications, macroscopic demonstrations based on thermodynamics and
fluctuations- dissipation theorems are constructed. For the first time a clear
summary and a critical review of previous results are given.


title: Internal avalanches in a pile of superconducting vortices

abstract:
  Using an array of miniature Hall probes, we monitored the spatiotemporal
variation of the internal magnetic induction in a superconducting niobium
sample during a slow sweep of external magnetic field. We found that a sizable
fraction of the increase in the local vortex population occurs in abrupt jumps.
The size distribution of these avalanches presents a power-law collapse on a
limited range. In contrast, at low temperatures and low fields, huge avalanches
with a typical size occur and the system does not display a well-defined
macroscopic critical current.


title:
Distribution of time-constants for tunneling through a 1D Disordered
  Chain

abstract:
  The dynamics of electronic tunneling through a disordered 1D chain of finite
length is considered. We calculate distributions of the transmission
coefficient T, Wigner delay time and, $\tau_\phi$ and the transport time,
$\tau_t=T\tau_\phi$. The central bodies of these distributions have a power-law
form, what can be understood in terms of the resonant tunneling through
localised states.


title:
On the localization of random heteropolymers at the interface between
  two selective solvents

abstract:
  To study the localization of random heteropolymers at an interface separating
two selective solvents within the model of Garel, Huse, Leibler and Orland,
Europhys. Lett. {\bf 8} 9 (1989), we propose an approach based on a
disorder-dependent real space renormalization procedure. This approach allows
to recover that a chain with a symmetric distribution in
hydrophobic/hydrophilic components is localized at any temperature in the
thermodynamic limit, whereas a dissymmetric distribution in
hydrophobic/hydrophilic components leads to a delocalization phase transition.
It yields in addition explicit expressions for the thermodynamic quantities as
well as a very detailed description of the statistical properties of the
behaviors of the heteropolymers in the high temperature limit. For the case of
a small dissymmetry in hydrophobic/hydrophilic components, the renormalization
approach yields explicit predictions for the delocalization transition
temperature and for the critical behaviors of various quantities : in
particular, the free energy presents an essential singularity at the
transition, the typical length of blobs in the preferred solvent diverges with
an essential singularity, whereas the typical length of blobs in the other
solvent diverges algebraically. Finite-size properties are also characterized
in details for both cases. In particular, we give the probability distribution
of the delocalization temperature for the ensemble of chains of finite (large)
length $L$. Finally, we discuss the non-equilibrium dynamics at temperature $T$
starting from a zero-temperature initial condition.


title:
Hole concentration induced transformation of the magnetic and orbital
  structure in Nd{1-x}Sr{x}MnO{3}

abstract:
  In order to study the magnetic and crystal structures in the
Nd{1-x}Sr{x}MnO{3} system, we have peformed neutron diffraction measurements on
melt-grown polycrystalline samples with 0.49 < x < 0.75. As a function of hole
concentration x, the system shows systematic transformation of magnetic and
crystal structures, which is consistently explained by the change of the
character of Mn eg orbitals. With increasing x, the Nd{1-x}Sr{x}MnO{3} system
exhibits a metallic ferromagnetic state, a metallic A-type AFM state, and then
an insulating C-type AFM state. The CE-type charge-ordered AFM state was
observed only in the vicinity of x=1/2, and it coexists with the A-type AFM
state for x > 1/2, indicating that the energy difference between these two
states is extremely small. We also found that the MnO{6} octahedra are apically
compressed in the CE-type and A-type AFM states due to the d(3x2-r2)/d(3y2-r2)
or d(x2-y2) orbital orderings, respectively, whereas they are apically
elongated by the rod-type d(3z2-r2) orbital ordering in the C-type AFM state.
In addition, a selective broadening of Bragg peaks was observed in the C-type
AFM phase, and its x dependence strongly suggests the charge ordering for a
commsurate value of the hole concentration at either x=3/4 or x=4/5.


title: Testing a Variational Approach to Random Directed Polymers

abstract:
  The one dimensional direct polymer in random media model is investigated
using a variational approach in the replica space. We demonstrate numerically
that the stable point is a maximum and the corresponding statistical properties
for the delta correlated potential are in good agreements with the known
analytic solution. In the case of power-law correlated potential two regimes
are recovered: a Flory scaling dependent on the exponent of the correlations,
and a short range regime in analogy with the delta-correlated potential case.


title:
Reply to comment on ``Dynamic scaling in the spatial distribution of
  persistent sites''

abstract:
  We reply to the comment cond-mat/9902073 by Ben-Naim and Krapivsky on our
paper cond-mat/9901130. We show that their arguments are incorrect, and present
more numerical results to back our earlier conclusions.


title: Quantum Transport in Disorderd Mesoscopic Ferromagnetic Films

abstract:
  The effect of impurity and domain-wall scattering on the electrical
conductivity of disordered mesoscopic magnetic thin films is studied by use of
computer simulation. The results indicate a reduction of resistivity due to a
domain wall, which is consistent with the explanation in terms of the dephasing
caused by domain wall.


title: Predictive Information

abstract:
  Observations on the past provide some hints about what will happen in the
future, and this can be quantified using information theory. The ``predictive
information'' defined in this way has connections to measures of complexity
that have been proposed both in the study of dynamical systems and in
mathematical statistics. In particular, the predictive information diverges
when the observed data stream allows us to learn an increasingly precise model
for the dynamics that generate the data, and the structure of this divergence
measures the complexity of the model. We argue that divergent contributions to
the predictive information provide the only measure of complexity or richness
that is consistent with certain plausible requirements.


title:
Statistics of Coulomb Blockade Peak Spacings within the Hartree-Fock
  Approximation

abstract:
  We study the effect of electronic interactions on the addition spectra and on
the energy level distributions of two-dimensional quantum dots with weak
disorder using the self-consistent Hartree-Fock approximation for spinless
electrons. We show that the distribution of the conductance peak spacings is
Gaussian with large fluctuations that exceed, in agreement with experiments,
the mean level spacing of the non-interacting system. We analyze this
distribution on the basis of Koopmans' theorem. We show furthermore that the
occupied and unoccupied Hartree-Fock levels exhibit Wigner-Dyson statistics.


title: Practical Methods for Ab Initio Calculations on Thousands of Atoms

abstract:
  We describe recent progress in developing practical ab initio methods for
which the computer effort is proportional to the number of atoms: linear
scaling or O(N) methods. It is shown that the locality property of the density
matrix gives a general framework for constructing such methods. We then
describe our scheme, which operates within density functional theory. Efficient
methods for reaching the electronic ground state are summarised, both for
finding the density matrix, and in varying the localised orbitals.


title:
Inelastic quantum transport in superlattices: success and failure of the
  Boltzmann equation

abstract:
  Electrical transport in semiconductor superlattices is studied within a fully
self-consistent quantum transport model based on nonequilibrium Green
functions, including phonon and impurity scattering. We compute both the drift
velocity-field relation and the momentum distribution function covering the
whole field range from linear response to negative differential conductivity.
The quantum results are compared with the respective results obtained from a
Monte Carlo solution of the Boltzmann equation. Our analysis thus sets the
limits of validity for the semiclassical theory in a nonlinear transport
situation in the presence of inelastic scattering.


title:
Effective Interactions Between Rigid Polyelectrolytes and Like-charged
  Planar Surfaces

abstract:
  We study the effective interaction between a planar array of uniformly
negatively charged, stiff rods parallel to a negatively charged planar
substrate in the absence of salt in a continuous, isotropic dielectric medium.
Using Brownian dynamics simulations, we examine the general effects of
counterion valence, rod spacing, macroion charge densities, and the rod size on
the attractive rod-surface interaction force. At room temperature divalent as
well as monovalent counterions mediate an interaction that can be repulsive or
attractive upon adjusting either the macroion charge densities or the rod
radius. Finally, we examine the effects of discretizing the surface charge as
laterally mobile monovalent anions and of electrostatic images in the
substrate.


title: 3D Spinodal Decomposition in the Inertial Regime

abstract:
  We simulate late-stage coarsening of a 3D symmetric binary fluid using a
lattice Boltzmann method. With reduced lengths and times l and t respectively
(scales set by viscosity, density and surface tension) our data sets cover 1 <
l < 10^5, 10 < t < 10^8. We achieve Reynolds numbers approaching 350. At Re >
100 we find clear evidence of Furukawa's inertial scaling (l ~ t^{2/3}),
although the crossover from the viscous regime (l ~ t) is very broad. Though it
cannot be ruled out, we find no indication that Re is self-limiting (l ~
t^{1/2}) as proposed by M. Grant and K. R. Elder [Phys. Rev. Lett. 82, 14
(1999)].


title:
Theoretical and Experimental Adsorption Studies of Polyelectrolytes on
  an Oppositely Charged Surface

abstract:
  Using self-assembly techniques, x-ray reflectivity measurements, and computer
simulations, we study the effective interaction between charged polymer rods
and surfaces. Long-time Brownian dynamics simulations are used to measure the
effective adhesion force acting on the rods in a model consisting of a planar
array of uniformly positively charged, stiff rods and a negatively charged
planar substrate in the presence of explicit monovalent counterions and added
monovalent salt ions in a continuous, isotropic dielectric medium. This
electrostatic model predicts an attractive polymer-surface adhesion force that
is weakly dependent on the bulk salt concentration and that shows fair
agreement with a Debye-Huckel approximation for the macroion interaction at
salt concentrations near 0.1 M. Complementary x-ray reflectivity experiments on
poly(diallyldimethyl ammonium) chloride (PDDA) monolayer films on the native
oxide of silicon show that monolayer structure, electron density, and surface
roughness are likewise independent of the bulk ionic strength of the solution.


title: Cu-63 NQR Measurement of Stripe Order Parameter in La(2-x)Sr(x)CuO(4)

abstract:
  We demonstrate that one can measure the charge-stripe order parameter in the
hole-doped CuO(2) planes of La(1.875)Ba(0.125)CuO(4),
La(1.48)Nd(0.4)Sr(0.12)CuO(4) and La(1.68)Eu(0.2)Sr(0.12)CuO(4) utilizing the
wipeout effects of Cu-63 NQR. Application of the same approach to
La(2-x)Sr(x)CuO(4) reveals the presence of similar stripe order for the entire
underdoped superconducting regime 1/16 < x < 1/8.


title: Quantum decoherence phenomena in thermal assisted tunneling

abstract:
  We propose a novel approach to the problem of a transition from quantum to
classical behavior in mesoscopic spin systems. This paper is intended to
demonstrate that main cause of such transitions is quantum decoherence which
appear as a result of a thermal interaction between spin system and its
environment.


title:
Optical detection of a BCS phase transition in a trapped gas of
  fermionic atoms

abstract:
  Light scattering from a spin-polarized degenerate Fermi gas of trapped
ultracold Li-6 atoms is studied. We find that the scattered light contains
information which directly reflects the quantum pair correlation due to the
formation of atomic Cooper pairs resulting from a BCS phase transition to a
superfluid state. Evidence for pairing can be observed in both the space and
time domains.


title:
Theory of the Josephson effect in superconductor / one-dimensional
  electron gas / superconductor junction

abstract:
  We present a theory for the Josephson effect in an unconventional
superconductor / one-dimensional electron gas / unconventional superconductor
(s/o/s) junction, where the Josephson current is carried by components injected
perpendicular to the interface. When superconductors on both sides have triplet
symmetries, the Josephson current is enhanced at low temperature due to the
zero-energy states formed near the interface. Measuring Josephson current in
this s/o/s junction, we can identify parity of the superconductor.


title:
Critical behavior of two-dimensional random hopping fermions with
  \pi-flux

abstract:
  A two dimensional random hopping model with N-species and \pi-flux is
studied. The field theory at the band center is shown to be in the universality
class of GL(4m,R)/O(4m) nonlinear sigma model. Vanishing beta function suggests
delocalised states at the band center. Contrary to the similar universality
class with broken time reversal symmetry, the present class is expected to have
at least two fixed point. Large N-systems are shown to be in the weak-coupling
fixed point, which is characterized by divergent density of state, while small
N systems may be in the strong-coupling fixed point.


title: Metallic Xenon. Conductivity or Superconductivity?

abstract:
  It is demonstrated that the point of view that metallization of xenon as a
result of a band - gap closure has some discrepancies with experimental result.
A superconductivity transition as an alternative possibility is examined. At
such supposition critical temperature of superconductivity transition T is
about 5000 K. A mechanism of inert gas condensation by virtual excitations of
molecular type is discussed.


title: A two step algorithm for learning from unspecific reinforcement

abstract:
  We study a simple learning model based on the Hebb rule to cope with
"delayed", unspecific reinforcement. In spite of the unspecific nature of the
information-feedback, convergence to asymptotically perfect generalization is
observed, with a rate depending, however, in a non- universal way on learning
parameters. Asymptotic convergence can be as fast as that of Hebbian learning,
but may be slower. Moreover, for a certain range of parameter settings, it
depends on initial conditions whether the system can reach the regime of
asymptotically perfect generalization, or rather approaches a stationary state
of poor generalization.


title:
The Effect of Ni and Zn Doping in Bi2212 from Tunneling Measurements.
  The MCS model of the High-Tc Superconductivity in hole-doped cuprates

abstract:
  We use Ni and Zn impurities doped into Bi2212 to test the MS (Magnetic
polaron - Spinon) model proposed earlier. We present electron-tunneling
spectroscopy of pure, Ni- and Zn-doped Bi2212 single crystals below Tc using a
break-junction technique. We show that the magnetic (Ni) and nonmagnetic (Zn)
impurities doped into CuO2 planes affect both Tc and the density of states in
Bi2212 but do it differently. In order to explain the data, we had to modify
the MS model. Thus, we present a Magnetic Coupling of Stripes (MCS) model. In
the MCS model, there is only one superconductivity - a spinon superconductivity
along charged stripes. The coherent state of the spinon superconductivity is
established by magnons which are excited by motions of charged stripes. So, in
the MCS model, the superconductivity has two mechanisms: along charged stripes
and perpendicular to stripes.


title:
Crossover Scales at the Critical Points of Fluids with Electrostatic
  Interactions

abstract:
  Criticality in a fluid of dielectric constant D that exhibits Ising-type
behavior is studied as additional electrostatic (i.e., ionic) interactions are
turned on. An exploratory perturbative calculation is performed for small
ionicity as measured by the ratio of the electrostatic energy to the strength
of the short-range nonionic (i.e., van der Waals) interactions in the uncharged
fluid.
  With the aid of distinct transformations for the short-range and for the
Coulombic interactions, an effective Hamiltonian with coefficients depending on
the ionicity is derived at the Debye-Hueckel limiting-law level for a fully
symmetric model. The crossover between classical (mean-field) and Ising
behavior is then estimated using a Ginzburg criterion. This indicates that the
reduced crossover temperature depends only weakly on the ionicity (and on the
range of the nonionic potentials); however, the trends do correlate with the,
much stronger, dependence observed experimentally.


title: Multipole excitations in quantum dots

abstract:
  We have employed time-dependent local-spin density theory to analyze the
multipole spin and charge density excitations recently found in GaAs-AlGaAs
quatum dots [C. Sch\"uller et al, Phys. Rev. Lett {\bf 80}, 2673 (1998)]. The
overall agreement between theory and experiment is good, identifying the
angular momentum of the modes observed in the experiment. We have found that
high multipolarity spin density edge modes originate from interband transitions
instead that from intraband transitions, as it happens in the dipole case.


title:
Molecular-Dynamics Simulation of a Glassy Polymer Melt: Rouse Model and
  Cage Effect

abstract:
  We report results of molecular-dynamics simulations for a glassy polymer melt
consisting of short, linear bead-spring chains. It was shown in previous work
that this onset of the glassy slowing down is compatible with the predictions
of the mode coupling theory. The physical process of `caging' of a monomer by
its spatial neighbors leads to a distinct two step behavior in the particle
mean square displacements. In this work we analyze the effects of this caging
process on the Rouse description of the melt's dynamics. We show that the Rouse
theory is applicable for length and time scales above the typical scales for
the caging process. Futhermore, the monomer displacement is compared with
simulation results for a binary Lennard-Jones mixture to point out the
differences which are introduced by the connectivity of the particles.


title:
Magnetic Field Effect in Josephson tunneling between d-Wave
  Superconductors

abstract:
  The magnetic field effect in the Josephson tunneling between two d-wave
superconductors are investigated. When the crystal orientation of one (or each)
superconductor relative to the interface normal is such that midgap states
exist at the interface, there is a component of the tunneling current due to
the midgap states. For a junction with a flat {001}|{110} or {100}|{110}
interface, this component is the predominant contribution to the current. The
predicted current-field dependence differs entirely from the conventional
Fraunhofer pattern, in agreement with a published measurement. This is because,
apart from the Fraunhofer factor, the critical current depends on the magnetic
field B through the current density also which is a linear function of B for
weak B.


title:
Quasiparticle Band Structure and Density Functional Theory:
  Single-Particle Excitations and Band Gaps in Lattice Models

abstract:
  We compare the quasiparticle band structure for a model insulator obtained
from the fluctuation exchange approximation (FEA) with the eigenvalues of the
corresponding density functional theory (DFT) and local density approximation
(LDA). The discontinuity in the exchange-correlation potential for this model
is small and the FEA and DFT band structures are in good agreement. In contrast
to conventional wisdom, the LDA for this model overestimates the size of the
band gap. We argue that this is a consequence of an FEA self-energy that is
strongly frequency dependent, but essentially local.


title: Difference between insulating and conducting states

abstract:
  It is proposed to used, as a basic property specifying the difference between
an insulator and a conductor, a static phenomenon, namely the field effect
which absent in the former, but present in the latter. The absence or present
of the field effect is closely associated with the nature of the homogenious
linear response to a static electric field. For an insulator, it is finite; for
a conductor, it depends on the volume V and tends to infinity when V to
infinity. The fluctuation-dissipation theorem makes it possibile to relate the
nature of this response to the mean square fluctuation of the dipole moment of
the system, which is normal in an insulator, but anomalious in a conductor. A
number of examples are considered. A notable property of the BCS
supercondctivity state have remarked, namely: its conductivity property is a
consequence of non-zero electron density fluctuations in the ground state of
the system with ODLRO.


title:
Breakdown of Scaling in the Nonequilibrium Critical Dynamics of the
  Two-Dimensional XY Model

abstract:
  The approach to equilibrium, from a nonequilibrium initial state, in a system
at its critical point is usually described by a scaling theory with a single
growing length scale, $\xi(t) \sim t^{1/z}$, where z is the dynamic exponent
that governs the equilibrium dynamics. We show that, for the 2D XY model, the
rate of approach to equilibrium depends on the initial condition. In
particular, $\xi(t) \sim t^{1/2}$ if no free vortices are present in the
initial state, while $\xi(t) \sim (t/\ln t)^{1/2}$ if free vortices are
present.


title:
Determination of optimal effective interactions between amino acids in
  globular proteins

abstract:
  An optimization technique is used to determine the pairwise interactions
between amino acids in globular proteins. A numerical strategy is applied to a
set of proteins for maximizing the native fold stability with respect to
alternative structures obtained by gapless threading. The extracted parameters
are shown to be very reliable for identifying the native states of proteins
(unrelated to those in the training set) among thousands of conformations. The
only poor performers are proteins with heme groups and/or poor compactness
whose complexity cannot be captured by standard pairwise energy functionals.


title: Magnetoplasmons in quantum rings

abstract:
  We have studied the structure and dipole charge density response of nanorings
as a function of the magnetic field using local-spin density functional theory.
Two small rings consisting of 12 and 22 electrons confined by a positively
charged background are used to represent the cases of a narrow and a wide ring.
The results are qualitatively compared with experimental data existing on
microrings and on antidots. A smaller ring containing 5 electrons is also
analyzed to allow for a closer comparison with a recent experiment on a two
electron quantum ring.


title: Level Correlations in Disordered Metals: the Replica sigma-Model

abstract:
  We compute energy level correlations in weakly disordered metallic grains
using the fermionic replica method. We use the standard sigma-model approach
and show that non--trivial saddle points, which break replica symmetry, must be
included in the calculation to reproduce the oscillatory behavior of the
correlations. We calculate the correlation functions in all three classical
ensembles GOE, GUE and GSE including the finite-dimensional gradient
corrections. Our results coincides with those obtained by the supersymmetric
sigma-model and the semi-classical trace formula.


title:
Instability of Non-vortex State toward a Quantized Vortex in
  Bose-Einstein Condensate under External Rotation

abstract:
  The instability condition of the non-vortex state toward vortex formation is
exa mined within the Bogoliubov theory when a Bose-Einstein condensate is under
exte rnally forced rotation. The obtained critical angular velocity combined
with the previous stability cond itions for a votex yields a detailed phase
diagram in the critical velocity vs t he system parameter. This facilitates
vortex formation experiments for alkali atom gases confined in a harmonic
potential.


title:
Multi-Self-Overlap Ensemble for protein folding: ground state search and
  thermodynamics

abstract:
  Long chains of the HP lattice protein model are studied by the
Multi-Self-Overlap Ensemble(MSOE) Monte Carlo method, which was developed
recently by the authors. MSOE successfully finds the lowest energy states
reported before for sequences of the chain length $N=42\sim 100$ in two and
three dimensions. Moreover, MSOE realizes the lowest energy state that ever
found in a case of N=100. Finite-temperature properties of these sequences are
also investigated by MSOE. Two successive transitions are observed between the
native and random coil states. Thermodynamic analysis suggests that the ground
state degeneracy is relevant to the order of the transitions in the HP model.


title:
Chiral Optical Absorption by a Vortex in p_x \pm i p_y-Wave
  Superconductor

abstract:
  The chiral optical absorption by a single vortex in a p_x \pm i p_y-wave
superconductor is studied theoretically. The p_x \pm i p_y-wave state was
recently suggested as the symmetry of the order parameter of Sr_2 Ru O_4
superconductor. Due to the violation of time reversal symmetry, there are two
types of vortices whose winding orientation is the same or opposite to the
angular momentum of the Cooper pair. In a real material domains with p_x \pm i
p_y-wave states are expected. However, optical absorption of circular polarized
light depends only on the winding of the vortex and has a low energy absorption
peak which results in dichroism. Dichroism occurs if superconductivity is
realized on a single Fermi surface sheet. However, in the case of several Fermi
surface sheets dichroism may disappear, if the both types of carriers are
present, electron-like and hole-like. Therefore chiral optical absorption is a
possible experiment to detect the orbital dependent superconductivity which was
suggested as the superconducting state of Sr_2 Ru O_4.


title:
Charge Segregation, Cluster Spin-Glass and Superconductivity in
  La1.94Sr0.06CuO4

abstract:
  A 63Cu and 139La NMR/NQR study of superconducting (Tc=7 K) La1.94Sr0.06CuO4
single crystal is reported. Coexistence of spin-glass and superconducting
phases is found below ~5 K from 139La NMR relaxation. 63Cu and 139La NMR
spectra show that, upon cooling, CuO2 planes progressively separate into two
magnetic phases, one of them having enhanced antiferromagnetic correlations.
These results establish the AF-cluster nature of the spin-glass. We discuss how
this phase can be related to the microsegregation of mobile holes and to the
possible pinning of charge-stripes.


title: Cohesion and conductance of disordered metallic point contacts

abstract:
  The cohesion and conductance of a point contact in a two-dimensional metallic
nanowire are investigated in an independent-electron model with hard-wall
boundary conditions. All properties of the nanowire are related to the Green's
function of the electronic scattering problem, which is solved exactly via a
modified recursive Green's function algorithm. Our results confirm the validity
of a previous approach based on the WKB approximation for a long constriction,
but find an enhancement of cohesion for shorter constrictions. Surprisingly,
the cohesion persists even after the last conductance channel has been closed.
For disordered nanowires, a statistical analysis yields well-defined peaks in
the conductance histograms even when individual conductance traces do not show
well-defined plateaus. The shifts of the peaks below integer multiples of
$2e^2/h$, as well as the peak heights and widths, are found to be in excellent
agreement with predictions based on random matrix theory, and are similar to
those observed experimentally. Thus abrupt changes in the wire geometry are not
necessary for reproducing the observed conductance histograms. The effect of
disorder on cohesion is found to be quite strong and very sensitive to the
particular configuration of impurities at the center of the constriction.


title: A monoclinic ferroelectric phase in the Pb(Zr1-xTix)O3 solid solution

abstract:
  A previously unreported ferroelectric phase has been revealed on a highly
homogeneous sample of Pb(Zr0.52Ti0.48)O3 by high-resolution synchrotron x-ray
powder diffraction measurements. At ambient temperature the sample has
tetragonal symmetry (at= 4.037 A, ct= 4.138 A), and transforms below ~250 K
into a phase which, unexpectedly, has monoclinic symmetry (am= 5.717 A, bm=
5.703 A, cm= 4.143 A, beta= 90.53 deg., at 20K). The intensity data strongly
indicate that the polar axis lies in the monoclinic ac plane close to the
pseudo-cubic [111] direction, which would be an example of the species
m3m(12)A2Fm predicted on symmetry grounds by Shuvalov.


title: A note on density correlations in the half-filled Hubbard model

abstract:
  We consider density-density correlations in the one-dimensional Hubbard model
at half filling. On intuitive grounds one might expect them to exhibit an
exponential decay. However, as has been noted recently, this is not obvious
from the Bethe Ansatz/conformal field theory (BA/CFT) approach. We show that by
supplementing the BA/CFT analysis with simple symmetry arguments one can easily
prove that correlations of the lattice density operators decay exponentially.


title: Boundary effects in reaction-diffusion processes

abstract:
  The effects of a boundary on reaction systems are examined in the framework
of the general single-species reaction/coalescence process. The boundary
naturally represents the reactants' container, but is applicable to exciton
dynamics in a doped TMMC crystal. We show that a density excess, which extends
into the system diffusively from the boundary, is formed in two dimensions and
below. This implies a surprising result for the magnetisation near a fixed spin
in the coarsening of the one-dimensional critical Ising model. The universal,
dimensionally-dependent functional forms of this density excess are given by an
exact solution and the field-theoretic renormalisation group.


title: Aperiodic Tilings on the Computer

abstract:
  We briefly review the standard methods used to construct quasiperiodic
tilings, such as the projection, the inflation, and the grid method. A number
of sample Mathematica programs, implementing the different approaches for one-
and two-dimensional examples, are discussed. Apart from small examples, the
corresponding programs are not contained in the text, but will be made
available in electronic form.


title:
Ground-state dispersion and density of states from path-integral Monte
  Carlo. Application to the lattice polaron

abstract:
  A formula is derived that relates the ground-state dispersion of a many-body
system with the end-to-end distribution of paths with open boundary conditions
in imaginary time. The formula does not involve the energy estimator. It allows
direct measurement of the ground-state dispersion by quantum Monte Carlo
methods without analytical continuation or auxiliary fitting. The formula is
applied to the lattice polaron problem. The exact polaron spectrum and density
of states are calculated for several models in one, two, and three dimensions.
In the adiabatic regime of the Holstein model, the polaron density of states
deviates spectacularly from the free-particle shape.


title: Theory of Tunneling for Rough Junctions

abstract:
  A formally exact expression for the tunneling current, for its separation
into specular and diffuse components, and for its directionality, is given for
a thick tunnel junction with rough interfaces in terms of the properties of
appropriately defined scattering amplitudes. An approximate evaluation yields
the relative magnitudes of the specular and diffuse components, and the angular
dependence of the diffuse component, in terms of certain statistical properties
of the junction interfaces.


title: Formation of Ramsey Fringes in Double Bose-Einstein Condensates

abstract:
  Numerical simulations of Ramsey fringe formation in double Bose condensates
are carried out in two spatial dimensions. The effects of meanfield
nonlinearity and diffusion in the condensates give rise to new features in the
Ramsey fringes, namely spatial variation and an asymmetry between positive and
negative field detunings. We introduce the concept of an effective detuning,
which for moderate interpulse times provides a qualitative understanding of the
new features.


title:
Density Matrix Renormalization Group Study of the Haldane Phase in
  Random One-Dimensional Antiferromagnets

abstract:
  It is conjectured that the Haldane phase of the S=1 antiferromagnetic
Heisenberg chain and the $S=1/2$ ferromagnetic-antiferromagnetic alternating
Heisenberg chain is stable against any strength of randomness, because of
imposed breakdown of translational symmetry. This conjecture is confirmed by
the density matrix renormalization group calculation of the string order
parameter and the energy gap distribution.


title:
Electric field dependent structural and vibrational properties of the
  Si(100)-H(2 \times 1) surface and its implications for STM induced hydrogen
  desorption

abstract:
  We report a first principles study of the structure and the vibrational
properties of the Si(100)-H(2 \times 1) surface in an electric field. The
calculated vibrational parameters are used to model the vibrational modes in
the presence of the electric field corresponding to a realistic STM tip-surface
geometry. We find that local one-phonon excitations have short lifetimes (10 ps
at room temperature) due to incoherent lateral diffusion, while diffusion of
local multi-phonon excitations are suppressed due to anharmonic frequency
shifts and have much longer lifetimes (10 ns at room temperature). We calculate
the implications for current induced desorption of H using a recently developed
first principles model of electron inelastic scattering. The calculations show
that inelastic scattering events with energy transfer $n \hbar \omega$, where
n>1, play an important role in the desorption process.


title: Photon transport in thin disordered slabs

abstract:
  We examine using Monte Carlo simulations, photon transport in optically
`thin' slabs whose thickness L is only a few times the transport mean free path
$l^{*}$, with particles of different scattering anisotropies. The confined
geometry causes an auto-selection of only photons with looping paths to remain
within the slab. The results of the Monte Carlo simulations are borne out by
our analytical treatment which incorporates the directional persistence by the
use of the Ornstein-Uhlenbeck process, which interpolates between the short
time ballistic and long time diffusive regimes.