pinecone/core-2020-05-10-deduplication huggingface dataset:
Many-body Green's function theory for thin ferromagnetic films: exact
  treatment of the single-ion anisotropy

A theory for the magnetization of ferromagnetic films is formulated within
the framework of many-body Green's funtion theory which considers all
components of the magnetization. The model Hamiltonian includes a Heisenberg
term, an external field, a second- and fourth-order uniaxial single-ion
anisotropy, and the magnetic dipole-dipole coupling. The single-ion anisotropy
terms can be treated exactly by introducing higher-order Green's functions and
subsequently taking advantage of relations between products of spin operators
which leads to an automatic closure of the hierarchy of the equations of motion
for the Green's functions with respect to the anisotropy terms. This is an
improvement on the method of our previous work, which treated the corresponding
terms only approximately by decoupling them at the level of the lowest-order
Green's functions. RPA-like approximations are used to decouple the exchange
terms in both the low-order and higher-order Green's functions. As a first
numerical example we apply the theory to a monolayer for spin S=1 in order to
demonstrate the superiority of the present treatment of the anisotropy terms
over the previous approximate decouplings.Comment: 23 pages, 5 figure
Ring current effects on the dielectric function of cylindrical
  nano-organic materials

We review recent results on the behaviour of the dielectric function of
cylindrical nano-organic materials at very low frequencies in a magnetic field.
For cylindrical structures - such as carbon nanotubes - the polarisability is
shown to be a discontinuous function of a longitudinal magnetic field where
plateau-like regions are separated by sudden jumps or peaks. A relation is
pointed out between each discontinuity in the polarisability and the cross-over
between ground and first excited states induced by the magnetic field. This one
to one correspondence suggests to use measurements of the dielectric function
in an applied magnetic field in order to obtain informations about the
electronic structures of cylindrical nanostructures. In addition, it is shown,
by studying finite graphene layers, that the measurement of the polarisability
in a magnetic field could be a powerful way for detecting possible edge-states
in amorphous carbon materials such as activated carbon fibres. Finally, the
importance of the electron-electron interaction is emphasised by discussing
examples of strongly interacting electrons on rings or cylinders, in the limit
of infinite interaction.Comment: 36 pages, 12 figure
Neutrino masses and particle physics beyond the standard model

The evidence for non-vanishing neutrino masses from solar and atmospheric
neutrinos provides the first solid hint towards physics beyond the standard
model. A full reconstruction of the neutrino spectrum may well provide a key to
the theoretical structures underlying the standard model such as supersymmetry,
grand unification or extra space dimensions. In this article we discuss the
impact of absolute neutrinos masses on physics beyond the standard model. We
review the information obtained from neutrino oscillation data and discuss the
prospects of the crucial determination of the absolute neutrino mass scale, as
well as the intriguing connection with the Z-burst model for extreme-energy
cosmic rays.Comment: 25 pages, 15 figures. Invited review for non-specialists, references
  adde
Screw dislocations in the field theory of elastoplasticity

A (microscopic) static elastoplastic field theory of dislocations with moment
and force stresses is considered. The relationship between the moment stress
and the Nye tensor is used for the dislocation Lagrangian. We discuss the
stress field of an infinitely long screw dislocation in a cylinder, a dipole of
screw dislocations and a coaxial screw dislocation in a finite cylinder. The
stress fields have no singularities in the dislocation core and they are
modified in the core due to the presence of localized moment stress.
Additionally, we calculated the elastoplastic energies for the screw
dislocation in a cylinder and the coaxial screw dislocation. For the coaxial
screw dislocation we find a modified formula for the so-called Eshelby twist
which depends on a specific intrinsic material length.Comment: 19 pages, LaTeX, 2 figures, Extended version of a contribution to the
  symposium on "Structured Media'' dedicated to the memory of Professor
  Ekkehart Kr\"oner, 16-21 September 2001, Pozna\'n, Poland. to appear in
  Annalen der Physik 11 (2002
Quantum spin chains with various defects

Using the density matrix renormalization group (DMRG) method, we study the
quantum coherence in one-dimensional disordered Fermi systems. We consider in
detail spinless fermions on a ring, and compare the influence of several kinds
of impurities in a gapless and a dimerized, gapped system. In the
translation-invariant system a so-called site-impurity, which can be realized
by a local potential or a change of one link, increases for repulsive
interaction and decreases for attractive interaction. The weakening of two
neighboring bonds, which is a realization of a so-called bond-impurity, on the
other hand, is healed for repulsive interaction, but enhanced for intermediate
attractive interactions. This leads to strong suppression of the quantum
coherence measured by the phase sensitivity, but not to localization. Adding a
local distortion to a dimerized system we find that even the presence of a
single site-impurity increases the metallic region found in the dimerized
model. For a strong dimerization and a high barrier, an additional sharp
maximum, even seen for systems with about 100 sites, occurs in the phase
sensitivity. A bond-impurity in the dimerized system also opens a small
metallic window in the otherwise isolating regime.Comment: 15 pages, 8 figures, replaced by final version, Journal-ref. adde
Microphase Separation within a Comb Copolymer with Attractive Side Chains: A Computer Simulation Study

Computer simulation modelling of a flexible comb copolymer with attractive interactions between the monomer units of the side chains is performed. The conditions for the coil-globule transition, induced by the increase of attractive interaction, ε, between side chain monomer units, are analysed for different values of the number of monomer units in the backbone, N, in the side chains, n, and between successive grafting points, m. It is shown that the coil-globule transition of such a copolymer corresponds to a first-order phase transition. The energy of attraction (ε) required for the realisation of the coil-globule transition decreases with increasing n and decreasing m. The coil-globule transition is accompanied by significant aggregation of side chain units. The resulting globule has a complex structure. In the case of a relatively short backbone (small value of N), the globule consists of a spherical core formed by side chains and an enveloping shell formed by the monomer units of the backbone. In the case of long copolymers (large value of N), the side chains form several spherical micelles while the backbone is wrapped on the surfaces of these micelles and between them.
The effect of the amido substituent on polymer molecular weight in propene homopolymerisation by titanium cyclopentadienyl-amide catalysts

In the homopolymerisation of propene by the cyclopentadienyl-amide titanium catalyst systems [η5,η1-C5H4(CH2)2NR]TiCl2/MAO and [η5,η1-C5H4(CH2)2NR]Ti(CH2Ph)2/B(C6F5)3 (R = tBu, iPr, Me), the catalyst with the smallest substituent (Me) on the amido moiety consistently gives the highest polymer molecular weight. This differs from the trend usually observed in related catalysts with tetramethylcyclopentadienyl-amide ancillary ligands, where larger amide substituents result in higher molecular weights. Based on the present information a hypothesis is formulated in which an increased cation-anion interaction for the less sterically hindered catalyst is responsible for disfavouring chain transfer relative to chain growth.
Determination of the reactivity ratios for the oxidative copolymerizations of indene with methyl, ethyl and butyl acrylates

Full Paper: The copolyperoxides of various compositions of indene with methyl acrylate, ethyl acrylate and butyl acrylate have been synthesized by the free-radical-initiated oxidative copolymerization. The compositions of copolyperoxide obtained from H-1 and C-13 NMR spectra have been used to determine the reactivity ratios of the monomers. The copolyperoxides contain a greater proportion of the indene units in random placement. The NMR studies have shown irregularities in the copolyperoxide chain due to the cleavage reactions of the propagating peroxide radical. The thermal analysis by differential scanning calorimetry suggests alternating peroxide units in the copolyperoxide chain. From the activation energy for the thermal degradation, it was inferred that degradation occurs via the dissociation of the peroxide (O-O) bonds of the copolyperoxide chain. The flexibility of the polyperoxides in terms of glass transition temperature (T-g) has also been examined
Pressure dependence of the low-frequency dielectric constant of KNbO_3

The effect of pressure on the low-frequency dielectric constant,
$\epsilon_0$, of single crystals of KNbO_3 is investigated by means of
capacitance measurements. The dielectric constant increases with pressure up to
22.5 kbar, where it exhibits a large value ($\epsilon_0$ = 5000), and then
decreases. This change in its behaviour is related to a phase transition
induced by pressure. On decompression, the samples do not revert back to the
ambient pressure phase.Comment: 4 pages latex, 1 postscript file include
One-step model of photoemission for non-local potentials

The one-step model of valence-band photoemission and inverse photoemission
from single-crystal surfaces is reformulated for generalized (non-local,
complex and energy-dependent) potentials. Thereby, it becomes possible to
account for self-energy corrections taken from many-body electronic-structure
calculations. The original formulation due to Pendry and co-workers employs the
KKR multiple-scattering theory for the calculation of the initial state. This
prevents a straightforward generalization of the one-step model to non-local
potentials. We therefore consider the Dyson equation which is set up within a
muffin-tin-orbitals representation as an alternative to obtain the
initial-state Green function. This approach requires a revision of the
transition-matrix elements which is carried out in detail. The final state is
considered as a time-reversed LEED state as usual. The proposed generalization
of the one-step model allows to distinguish between the bare photocurrent
reflecting the (quasi-particle) band structure and the secondary effects due to
the (dipole) selection rules and due to the wave-vector and energy dependence
of the transition-matrix elements.Comment: Revtex, 20 pages, no figures, phys. stat. sol. (b) 203 (in press
Study of Balance Equations for Hot-Electron Transport in an Arbitrary
  Energy Band (III)

By choosing an electron gas resting instead of drifting in the laboratory
coordinate system as the initial state, the first order perturbation
calculation of the previous paper (Phys. Stat. Sol. (b) 198, 785(1996)) is
revised and extended to include the high order field corrections in the
expression for the frictional forces and the energy transfer rates. The final
expressions are formally the same as those in first order in the electric
field, but the distribution functions of electrons appearing in them are
defined by different expressions. The problems relative to the distribution
function are discussed in detail and a new closed expression for the
distribution function is obtained. The nonlinear impurity-limited resistance of
a strong degenerate electron gas is computed numerically. The result calculated
by using the new expression for the distribution function is quite different
from that using the displaced Fermi function when the electric field is
sufficiently high.Comment: 15 pages with 3 PS figures, RevTeX, to be published in Physica Status
  Solidi (b
Thermodynamics of pseudospin-electron model in mean field approximation

The mean field type approach based on the self-consistent consideration of an
effective field created by electron transfer is developed for a description of
thermodynamics of the Hubbard type models with an infinitely large on-site
repulsion. This procedure, formulated by Izyumov et al, is an extension of the
recently proposed generalized random phase approximation(GRPA).
  Within this approach, the thermodynamic properties of the two-sublattice
pseudospin-electron model (the Hubbard model with local anharmonicity) are
studied. Such a model can be used for a description of dielectric properties of
YBaCuO-type superconductors along c-axis; pseudospins represent anharmonic
motions of apical oxygens O4. It is shown that there are either phase
transitions in the model with jumps of the mean values of a pseudospin and of
electron concentration (in the $\mu=const$ regime) or the phase separation (in
the $n=const$ regime). The phase transitions or phase separation are caused by
pseudospin-pseudospin interaction as well as by electron transfer (the latter
results in appearing of effective interaction between pseudospins). The
possibility of the ferroelectric type ordering of pseudospins is investigated.Comment: 17 pages, 7 figure
Electron states in a one-dimensional random binary alloy

We present a model for alloys of compound semiconductors by introducing a
one-dimensional binary random system where impurities are placed in one
sublattice while host atoms lie on the other sublattice. The source of disorder
is the stochastic fluctuation of the impurity energy from site to site.
Although the system is one-dimensional and random, we demonstrate analytical
and numerically the existence of extended states in the neighborhood of a given
resonant energy, which match that of the host atoms.Comment: 11 pages, REVTeX, 3 PostScript figure
Magnons in the ferromagnetic Kondo-lattice model

The magnetic properties of the ferromagnetic Kondo-lattice model (FKLM) are
investigated. Starting from an analysis of the magnon spectrum in the spin-wave
regime, we examine the ferromagnetic stability as a function of the occupation
of the conduction band $n$ and the strength $J$ of the coupling between the
localised moments and the conduction electrons. From the properties of the
spin-wave stiffness $D$ the ferromagnetic phase at zero temperature is derived.
Using an approximate formula the critical temperature $T_c$ is calculated as a
function of $J$ and $n$.Comment: 15 pages, 6 figures, to appear in phys. stat. sol.
FIR absorption in CdSe quantum dot ensembles

Absorption of far-infrared (FIR) radiation in very small CdSe crystallites (quantum dots, QDs) via excitation of confined dipolar vibrational modes was studied, both theoretically and experimentally.
Spatial quantisation of optical phonons was analysed in the framework of a continuum model, which couples the phonon amplitude to the electrostatic potential via the Fro¨ hlich interaction. The frequencies and oscillator strengths of the dipole-active optical vibration modes are presented calculated for a spherical QD, and for the first time for II–VI QDs these quantised modes were observed experimentally. Another effect studied in this work is the influence of the QD concentration
on the FIR absorption of their ensemble. It is shown that the dipole–dipole interaction becomes very important in dense QD ensembles and leads to smearing of the structure in the CdSe phonon band as the QD concentration increases.Fundação para a Ciência e a Tecnologia (FCT
Many Body Diffusion and Interacting Electrons in a Harmonic Confinement

We present numerically exact energy estimates for two-dimensional electrons
in a parabolic confinement. By application of an extension of the recently
introduced many-body diffusion algorithm, the ground-state energies are
simulated very efficiently. The new algorithm relies on partial
antisymmetrization under permutation of particle coordinates. A comparison is
made with earlier theoretical results for that system.Comment: Revised version, submitted to Phys. Rev. B E-mail adresses:
  Brosens@uia.ua.ac.be; Devreese@uia.ua.ac.be; Lcnlmmns@ruca.ua.ac.b
Resonant versus anti-resonant tunneling at carbon nanotube A-B-A
  heterostructures

Narrow antiresonances going to zero transmission are found to occur for
general (2n,0)(n,n)(2n,0) carbon nanotube heterostructures, whereas the
complementary configuration, (n,n)(2n,0)(n,n), displays simple resonant
tunneling behaviour. We compute examples for different cases, and give a simple
explanation for the appearance of antiresonances in one case but not in the
other. Conditions and ranges for the occurence of these different behaviors are
stated. The phenomenon of anti-resonant tunneling, which has passed unnoticed
in previous studies of nanotube heterostructures, adds up to the rich set of
behaviors available to nanotube based quantum effect devices.Comment: Published in phys. stat. sol. (b); 6 pages, 4 figure
Photoluminescence of the incompressible Laughlin liquid: Excitons,
  charged excitons, and fractionally charged excitons

The photoluminescence (PL) of a two-dimensional electron gas (2DEG) in a high
magnetic field is studied as a function of the filling factor and the
separation d between the electron layer and the valence hole. Depending on the
magnitude of d relative to the magnetic length lambda, two distinct regimes in
the response of the 2DEG to the valence hole occur, with different elementary
emission processes contributing to the PL spectrum. At d<lambda ("strong
coupling" regime), the hole binds one or two electrons to form an exciton (X)
or one of three possible charged exciton (X-) states, a spin-singlet or one of
two spin-triplets. At d>lambda ("weak coupling" regime), the hole decouples or
binds one or two Laughlin quasielectrons to form fractionally charged excitons
(FCX's). The binding energies as well as the emission energies and intensities
of all X- and FCX states are calculated.Comment: 9 pages, 6 figures, sumbitted to physica status solidi (b
A Model to Describe Transport Properties in
  $Bi_2Sr_2(Ca_zPr_{1-z})Cu_2O_{8+y}$

A pseudo-spin model is proposed, as a means to describe some transport
properties (resistivity and Hall mobility) in
$Bi_2Sr_2(Ca_zPr_{1-z})Cu_2O_{8+y}$. Our model is based in a double-well
potential where tunneling in a given site and interaction between different
lattice sites are allowed only through the excited states. Doping of the pure
system by the addition of $Pr$ increases the ratio between the activation
energy and the tunneling constant. The model Hamiltonian displays some features
which are present in the hydrogen-bonded ferroelectrics. Its dynamics is
treated in the random phase approximation and the characteristic frequency
(time) is used in a Drude formula in order to obtain some transport properties
of the system, namely the electric resistivity and the Hall mobility. The
quantities calculated in this work are compared with the experimental data of
B. Beschoten, S. Sadewasser, G. G\"{u}ntherodt and C. Quitmann [Phys. Rev.
Lett.77, 1837(1996)].Comment: 14 pages, 4 figure
Van Hove Singularity and Superconductivity in Disordered Hubbard Model

We apply the Coherent Potential Approximation (CPA) to a simple extended
Hubbard model with a nearest and next nearest neighbour hopping for disordered
superconductors with s-, d- and p-wave pairing. We show how the Van Hove
singularities in the electron density of states enhance the transition
temperature Tc for exotic superconductors in a clean and weakly disordered
system. The Anderson theorem and pair-breaking effects in presence of Van Hove
singularity caused by non-magnetic disorder are also discussed.Comment: REVTEX 40 pages, 8 figures, (accepted by Physica Status Solidi b
Thermodynamical Cross-Relations for Superconductors at the Critical
  Point

We investigate superconducting systems with the use of the phenomenological
Landau's theory of second order phase transitions, including into the
considerations the critical behaviour of the chemical potential. We derive in
this way a variety of new thermodynamical relations at the critical point.
Twelve basic relations connect critical jumps of different thermodynamical
quantites (specific heat, chemical potential derivatives with respect to
temperature, pressure (volume) and number of particles, volume (pressure)
derivatives with respect to temperature and pressure (volume)) with the
critical temperature or its derivatives with respect to the number of particles
or pressure (volume). These relations allow to find plenty of cross-relations
between different quantities at the critical point. The derived formulae can
practically be used in many cases to find such thermodynamical quantities at
the critical point which are extremely difficult to measure under the
assumption that the other ones are already known. We additionally perform a
test of the two derived relations by using two-band microscopic model,
describing superconducting systems. We calculate the specific heat, order
parameter and chemical potential as functions of temperature to show that the
tested relations are very well fulfilled.Comment: phys.stat.sol. (b) 231, No. 2, 299-312 (2002
Influence of Growth Parameters on the Surface and Interface Quality of Laser Deposited InSb/CdTe Heterostructures

The pulsed laser deposition technique has been employed for the growth of single crystalline oriented films of indium antimonide on bulk cadmium telluride substrates. The films grown during this study were tested for surface quality and interface features, generally prevalent due to film-substrate reactions. The composition of the grown film was found to deviate from that of the target owing to loss of antimony during evaporation, leading to the formation of an interfacial compound. The antimony deficiency in the films was compensated by correcting the target composition. Growth parameters and their effects on these manifestations have been studied. The optimization of these parameters has led to growth of layers with good surface morphology and abrupt interfaces. Efforts have been made to detect the origin of the diffuse interface and to identify the compound resulting at the interface through photoluminescence spectroscopy. Using PL and thermoenergetic calculations for the plausible reactions at the interface, we have ascertained that the interfacial compound is more likely to be In2Te3.\ud
\u
Excitonic Effects in Quantum Wires

We review the effects of Coulomb correlation on the linear and non-linear
optical properties of semiconductor quantum wires, with emphasis on recent
results for the bound excitonic states. Our theoretical approach is based on
generalized semiconductor Bloch equations, and allows full three-dimensional
multisubband description of electron-hole correlation for arbitrary confinement
profiles. In particular, we consider V- and T-shaped structures for which
significant experimental advances were obtained recently. Above band gap, a
very general result obtained by this approach is that electron-hole Coulomb
correlation removes the inverse-square-root single-particle singularity in the
optical spectra at band edge, in agreement with previous reports from purely
one-dimensional models. Strong correlation effects on transitions in the
continuum are found to persist also at high densities of photoexcited carriers.
  Below bandgap, we find that the same potential- (Coulomb) to kinetic-energy
ratio holds for quite different wire cross sections and compositions. As a
consequence, we identify a shape- and barrier-independent parameter that
governs a universal scaling law for exciton binding energy with size. Previous
indications that the shape of the wire cross-section may have important effects
on exciton binding are discussed in the light of the present results.Comment: Proc. OECS-5 Conference, G\"ottingen, 1997 (To appear in Phys. Stat.
  Sol. (b)