pinecone/core-2020-05-10-deduplication huggingface dataset:
Exact Solutions of Two-Band Models of Graded-Gap Superlattices

We have theoretically investigated two-band models of graded-gap
superlattices within the envelope-function approximation. Assuming that the gap
varies linearly with spatial coordinate, we are able to find exact solutions of
the corresponding Dirac-like equation describing the conduction- and
valence-band envelope-functions. The dispersion relation inside allowed
miniband of the superlattice may be expressed in terms of confluent
hypergeometric functions in a closed form.Comment: 7 pages in REVTeX 3.0. 1 Figure on request to F. D-A
  (fimat02@emducms1.sis.ucm.es). FM-UCM-3
Electron Structure Near Abrupt Edges in 2DEG under Strong Magnetic Field

Energies and wave functions of edge states in twodimensional electron gas are
evaluated for a finite step potential barrier model. The spectrum, instead of
smooth bending of Landau branches in the vicinity of the barrier acquires a
steplike form; unexpected edge plateaus and significant energy gap reduction
take place between the neighbouring Landau branches above the barrier tops. The
origin of these phenomena is traced. Stability with respect to modifications is
established. Manifestation of the qualitatively new features of electron
densities of states in abrupt confinements through magnetooptical and nuclear
magnetic spin relaxation effects is proposed.Comment: 24 pages in LATEX, 7 figures available on request, to appear in
  physica status solidi(b
High pressure magnetophotoluminescence in diluted magnetic semiconductors Cd1-xMnxSe and Cd1-xCoxSe

This paper reviews experimental studies on the magnetophotoluminescence in diluted magnetic semiconductors Cd1-xMnxSe with x = 0.01, 0.05, 0.10, and 0.25 and Cd1-xCoxSe with x = 0.012 at 1.4 and 4.2 K under hydrostatic pressures up to 2 GPa. The studies focus attention to the pressure dependence of the magnetic dichroism of the 1 s exciton state under magnetic fields of 0 to 27 T. Pressure strengthens the exciton-Mn(Co) and Mn(Co)-Mn(Co) exchange interactions. An analysis of these results in terms of the kinetic exchange theory shows that the on-site Coulomb energy U and the charge transfer energy ⊿ are reduced markedly by pressure
Electron transport in the Anderson model

Based on a selfconsistent theory of localization we study the electron
transport properties of a disordered system in the framework of the Anderson
model on a Bethe lattice. In the calculation of the dc conductivity we
separately discuss the two contributions to the current-current correlation
function dominating its behaviour for small and large disorder. The resulting
conductivity abruptly vanishes at a critical disorder strength marking the
localization transition.Comment: 7 pages, 3 figures; Proceedings of the 10th Conference on Hopping and
  Related Phenomena (Triest 2003
Coulomb gap and variable range hopping in a pinned Wigner crystal

It is shown that pinning of an electron Wigner crystal by a small
concentration of charged impurities creates the finite density of charged
localized states near the Fermi level. In the case of residual impurities in
the spacer this density of states is related to nonlinear screening of a close
acceptor by a Wigner crystal vacancy. On the other hand, intentional doping by
a remote layer of donors is a source of a long range potential, which generates
dislocations in Wigner crystal. Dislocations in turn create charged localized
states near the Fermi level. In both cases Coulomb interaction of localized
states leads to the soft Coulomb gap and ES variable range hopping at low
enough temperatures.Comment: To be published in proceedings of 10th conference on hopping and
  related phenomena in Physica Status Solid
Electronic and optical properties of InAs(110)

The electronic and optical properties of the cleavage InAs(110) surface are
studied using a semi-empirical tight-binding method which employs an extended
atomic-like basis set. We describe and discuss the electronic character of the
surface electronic states and we compare with other theoretical approaches, and
with experimental observations. We calculate the surface electronic band
structure and the Reflectance Anisotropy Spectrum, which are described and
discussed in terms of the surface electronic states and the atomic structure.Comment: 15 pages + 4 figures, submitted to PR
Exciton–biexciton quantum coherence and polaritonic stop-band transparency in CuCl.

A coherently driven exciton-biexciton transition in CuCl enables one to propagate a probe light beam within the exciton-polariton stop-band where radiation is otherwise completely reflected. The stop-band transparency window can be controlled via the pump beam frequency and intensity. The phenomenon is reminiscent of quantum coherence effects occurring in three-level atomic systems, except that it here involves delocalized electronic excitations in a crystal via a frequency and wave-vector selective polaritonic mechanism. Both a free standing slab and a microcavity configuration are theoretically studied
Quantum theory of photonic crystal polaritons

We formulate a full quantum mechanical theory of the interaction between
electromagnetic modes in photonic crystal slabs and quantum well excitons
embedded in the photonic structure. We apply the formalism to a high index
dielectric layer with a periodic patterning suspended in air. The strong
coupling between electromagnetic modes lying above the cladding light line and
exciton center of mass eigenfunctions manifests itself with the typical
anticrossing behavior. The resulting band dispersion corresponds to the
quasi-particles coming from the mixing of electromagnetic and material
excitations, which we call photonic crystal polaritons. We compare the results
obtained by using the quantum theory to variable angle reflectance spectra
coming from a scattering matrix approach, and we find very good quantitative
agreement.Comment: Proceedings of the "8th Conference on Optics of Excitons in Confined
  Systems" (OECS-8), 15-17 September 2003, Lecce (Italy
Excitonic Mott transition in double quantum wells

We consider an electron-hole system in double quantum wells theoretically. We
demonstrate that there is a temperature interval over which an abrupt jump in
the value of the ionization degree occurs with an increase of the carrier
density or temperature. The opposite effect - the collapse of the ionized
electron-hole plasma into an insulating exciton system - should occur at lower
densities. In addition, we predict that under certain conditions there will be
a sharp decrease of the ionization degree with increasing temperature - the
anomalous Mott transition. We discuss how these effects could be observed
experimentally.Comment: 6 pages, 4 figure
Direct measurement of the electron-phonon relaxation rate in thin copper
  films

We have used normal metal-insulator-superconductor (NIS) tunnel junction
pairs, known as SINIS structures, for ultrasensitive thermometry at sub-Kelvin
temperatures. With the help of these thermometers, we have developed an
ac-technique to measure the electron-phonon (e-p) scattering rate directly,
without any other material or geometry dependent parameters, based on
overheating the electron gas. The technique is based on Joule heating the
electrons in the frequency range DC-10 MHz, and measuring the electron
temperature in DC. Because of the nonlinearity of the electron-phonon coupling
with respect to temperature, even the DC response will be affected, when the
heating frequency reaches the natural cut-off determined by the e-p scattering
rate. Results on thin Cu films show a $T^{4}$ behavior for the scattering rate,
in agreement with indirect measurement of similar samples and numerical
modeling of the non-linear response.Comment: to appear in Phys. Stat. Solidi (2005
Electron-phonon interaction in thin copper and gold films

We have studied the electron-phonon (e-p) interaction in thin Cu and Au films
at sub-Kelvin temperatures with the help of the hot electron effect, using
symmetric normal metal-insulator-superconductor tunnel junction pairs as
thermometers. By Joule heating the electron gas and measuring the electron and
the lattice temperatures simultaneously, we show that the electron-phonon
scattering rate follows a $T^{4}$ temperature dependence in both metals. The
result is in accordance with the theory of e-p scattering in disordered films
with vibrating boudaries and impurities, in contrast to the $T^{3}$-law
expected for pure samples, and $T^{2}$-law for static disorder.Comment: to appear in Phys. Stat. Solidi (2005
The connection between elastic scattering cross sections and acoustic
  vibrations of an embedded nanoparticle

Arbitrary waves incident on a solid embedded nanoparticle are studied. The
acoustic vibrational frequencies are shown to correspond to the poles of the
scattering cross section in the complex frequency plane. The location of the
poles is unchanged even if the incident wave is nonplanar. A second approach
approximating the infinite matrix as a very large shell surrounding the
nanoparticle provides an alternate way of predicting the mode frequencies. The
wave function of the vibration is also provided.Comment: Accepted for publication in physica status solidi (c) (C) (2003)
  WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Proceedings of Phonons200
Electron-phonon interaction in correlated electronic systems: polarons
  and the formation of orbital ordering

The properties of a dilute electron gas, coupled to the lattice degrees of
freedom, are studied and compared with the properties of an electron gas at
half-filling, where spinless fermions with two orbitals per lattice site are
considered. The simplest model which includes both the local electron-lattice
interaction of the Jahn-Teller type and the electronic correlations is the
$E\otimes\beta$-Jahn-Teller-Hubbard model. We analyze the formation and
stability of Jahn-Teller polarons and bipolarons, respectively. Our approach is
based on a hopping expansion in the strong-coupling regime. The results are
compared with recently published findings for the Hubbard-Holstein model [1,2].
The special case of the Jahn-Teller-Hubbard model at half-filling is mapped on
a spin-1/2 Heisenberg model with phonon-dependent coupling constants. This has
been derived within a projection formalism that provides a continued-fraction
representation of the Green's function. We study the exact solution for two and
three particles and compare it with the effective theory on the infinite
lattice with one particle per site.Comment: 4 pages, 0 figures, submitted to Phonons2004, to appear in physica
  status solid
Atomic vibrations in disordered systems: Comparison of disordered
  diamond lattices and a realistic amorphous silicon model

Force-constant and positional disorder have been introduced into diamond
lattice models in an attempt to mimic the vibrational properties of a realistic
amorphous silicon model. Neither type of disorder is sufficient on its own to
mimic the realistic model. By comparing the spectral densities of these models,
it is shown that a combination of both disorders is a better representation,
but still not completely satisfactory. Topological disorder in these models was
investigated by renumbering the atoms and examining the dynamical matrix
graphically. The dynamical matrix of the realistic model is similar to that of
a positionally-disordered lattice model, implying that the short-range order in
both systems is similar.Comment: 4 pages; 3 figures; based on poster presentation for "Phonons 2004"
  conferenc
Reorientation in Antiferromagnetic Multilayers: Spin-Flop Transition and
  Surface Effects

Nanoscale superlattices with uniaxial ferromagnetic layers
antiferromagnetically coupled through non-magnetic spacers are recently used as
components of magnetoresistive and recording devices. In the last years
intensive experimental investigations of these artificial antiferromagnets have
revealed a large variety of surface induced reorientational effects and other
remarkable phenomena unknown in other magnetic materials. In this paper we
review and generalize theoretical results, which enable a consistent
description of the complex magnetization processes in antiferromagnetic
multilayers, and we explain the responsible physical mechanism. The general
structure of phase diagrams for magnetic states in these systems is discussed.
In particular, our results resolve the long standing problem of a ``surface
spin-flop'' in antiferromagnetic layers. This explains the different appearance
of field-driven reorientation transitions in systems like Fe/Cr (001) and (211)
superlattices, and in [CoPt]/Ru multilayers with strong perpendicular
anisotropy.Comment: Companion paper for talk at Second Seeheim Conference on Magnetism,
  June 27- July 1, 2004; 8 pages included 7 figure
Influence of surface anisotropy on the magnetization reversal of
  nanoparticles

The influence of surface anisotropy on the magnetization processes of
maghemite nanoparticles with ellipsoidal shape is studied by means of Monte
Carlo simulations. Radial surface anisotropy is found to favor the formation of
hedgehog-like spin structures that become more stable as the surface anisotropy
constant at the surface $k_S$ is increased form the value at the core. We have
studied the change in the low temperature hysteresis loops with the particle
aspect ratio and with $k_S$, finding a change in the magnetization reversal
mode as $k_S$ or the particle elongation is increased.Comment: Contribution to SCM2004 (2nd Seeheim Conference on Magnetism), to be
  published in Physica Status Solidi A. 4 pages, 2 figure
Systematic UHV-AFM experiments on Na nano-particles and nano-structures in NaCl

Results of systematic AFM (atomic force microscopy) experiments on heavily and moderatly irradiated NaCl samples are presented. The sodium nanoparticles and structures of nanoparticles are poduced in sodium chloride during irradiation. The AFM images of the nanoparticles have been obtained in ultra high vacuum (UHV) in the non-contact mode with an Omicron UHV AFM/STM system. The sizes and arrangements of the observed particles depend on the irradiation conditions. The melting behaviour of the sodium nanoclusters has been studied for these samples by differential scanning calorimetry (DSC). A phenomenological model has been proposed which explains the observed behaviour by the existence of two different structural states in the population of sodium colloids. AFM measurements of heavily irradiated natural rock salt samples have revealed ring- and chain-like clusters (or agglomerates) of Na colloid particles.
Melting properties of radiation-induced Na and Cl2 precipitates in ultra-heavily irradiated NaCl

Exposure of NaCl to high doses of ionizing radiation leads to the formation of nano-particles of metallic Na, very small chlorine precipitates, vacancy voids, and dislocations. A useful way to monitor the stage of the damage formation process is measuring the latent heat of melting of the Na-particles (~100°C) and chlorine precipitates (-101°C). In this paper we will present data, showing that for doses in the range of TRad (1010 Gy) the concentration of radiolytic Na may become very large. Even in pure samples, we have converted more than 20% of all NaCl molecules into metallic Na and chlorine, but often higher percentages can be achieved. In this paper we will present new data obtained for ultra-high irradiation doses and a first attempt will be made to understand the results.
Nucleation and growth of sodium colloids in NaCl under irradiation: theory and experiment

A mechanism of radiation-induced emission of Schottky defects from extended defects proposed originally for metals has recently been applied to ionic crystals, where it is based on interactions of excitons with extended defects such as dislocations and colloids. Exciton trapping and decay at colloids may result in the emission of F centers and consequent shrinkage of the colloid. In the present paper, the radiation-induced emission of F centers is taken into account in the modeling of nucleation and growth of sodium colloids and chlorine bubbles in NaCl exposed to electron or gamma irradiation. The evolution of colloid and bubble number densities and volume fractions with increasing irradiation dose is modeled in the framework of a modified rate theory and compared with experimental data. Experimental values of the colloid volume fractions and number densities have been estimated on the basis of latent heat of melting of metallic Na obtained with combined differential scanning calorimetry experiments and atomic force microscopy investigations of metallic clusters.
A many-body approach to crystal field theory

A self-consistent many-body approach is proposed to build a first-principles
crystal field theory, where crystal field parameters are calculated ab initio.
Many-body theory is used to write the energy of the interacting system as a
function of the density matrix of the noninteracting system. A variation of the
energy with respect to the density matrix gives an effective Hamiltonian that
is diagonalized to determine the density matrix providing the lowest energy.
The equations are written in terms of the Hopf algebra of functional
derivatives with respect to external fermionic sources. This approach contains
the many-body theory of Green functions as a special case, and the usual
crystal field theory as a first approximation. Therefore, it is expected to
provide good results for strongly-interacting electron systems.Comment: Equation (8) and references are correcte
Compressibility in the Integer Quantum Hall Effect within Hartree-Fock
  Approximation

Electron-electron interactions seem to play a surprisingly small role in the
description of the integer quantum Hall effect, considering that for just
slightly different filling factors the interactions are of utmost importance
causing the interaction-mediated fractional quantum Hall effect. However,
recent imaging experiments by Cobden et al. and Ilani et al. constitute strong
evidence for the importance of electron-electron interactions even in the
integer effect. The experiments report on measurements of the conductance and
electronic compressibility of mesoscopic MOSFET devices that show disagreement
with predictions from the single particle model. By diagonalising a random
distribution of Gaussian scatterers and treating the interactions in
Hartree-Fock approximation we investigate the role of electron-electron
interactions for the integer quantum Hall effect and find good agreement with
the experimental results.Comment: 4 pages, 4 figures, Proceedings of "Transport in Interacting and
  Disordered Systems (TIDS11)", submitted for publication in phys. stat. sol.
  (c), including pss style file
Scaling at the Energy-driven Metal-Insulator Transition and the
  Thermoelectric Power

The electronic properties of disordered systems at the Anderson
metal-insulator transition (MIT) have been the subject of intense study for
several decades. Thermoelectric properties at the MIT, such as thermopower and
thermal conductivity, however, have been relatively neglected. Using the
recursive Green's function method and the Chester-Thellung-Kubo-Greenwood
formalism, we calculate numerically the low temperature behaviour of all
kinetic coefficients. From these we can deduce for example the electrical
conductivity and the thermopower at finite temperatures. Here we present
results for the case of completely coherent transport in cubic 3D systems.Comment: 4 pages, 4 figures, Proceedings of "Transport in Interacting and
  Disordered Systems (TIDS11)", submitted for publication in phys. stat. sol.
  (c), including pss style file
Magneto-optical Faraday effect in II–VI based semimagnetic semiconductor nanocrystals

Different physical and chemical methods were used to prepare II–VI based semimagnetic semiconductor
nanocrystals. A study of magneto-optical Faraday effect in the nanocrystals revealed its enhancement as
compared with bulk crystals. It is explained in framework of increase in the oscillator strength of exciton
transitions and to the difference between these strengths in an external magnetic field. It was observed almost
linear dependence of the Faraday rotation as function of magnetic field strength for nanocrystals at
liquid helium temperature in contrast to the dependence with saturation in bulk case and changes in process
of a transition of the semimagnetic nanocrystals from the paramagnetic state to a spin glass state
Quantum kinetic theory of phonon-assisted carrier transitions in
  nitride-based quantum-dot systems

A microscopic theory for the interaction of carriers with LO phonons is used
to study the ultrafast carrier dynamics in nitride-based semiconductor quantum
dots. It is shown that the efficiency of scattering processes is directly
linked to quasi-particle renormalizations. The electronic states of the
interacting system are strongly modified by the combined influence of quantum
confinement and polar coupling. Inherent electrostatic fields, typical for
InGaN/GaN quantum dots, do not limit the fast scattering channels.Comment: 4 pages, 3 figures, accepted for publication in EPJ
A semiconducting nanotube quantumdot: effect of the form of the confinement potential

This is the author's final draft of the paper published as Physica Status Solidi C: Conferences, 2006, 3 (11), pp. 3959 - 3962.  The definitive version is available at www3.interscience.wiley.com.  Doi: 10.1002/pssc.200671595The states of a few (2-6) interacting electrons in a semiconducting carbon nanotube quantum dot are investigated for two extremes of the quantum dot confinement potential: harmonic and hard wall. The interacting electron states are calculated by exact diagonalisation of a single band, effective mass Hamiltonian, then the quantum dot addition energies and few particle densities are compared for the two types of confinement. By changing the harmonic confinement strength the system can be driven between the strongly and weakly correlated regimes, whereas for hard wall confinement the electrons are almost always strongly correlated. With hard wall or weak harmonic confinement the electrons localise and form Wigner crystal-like states
Transitions between electron-molecule states in electrostatic quantum
  dots

Intermediate spin states that occur in electrostatic dots in the magnetic
field regime just beyond the maximum density droplet are investigated. The
5-electron system is studied with exact diagonalization and group theory. The
results indicate that the intermediate spin states are mixed symmetry states
with a superposition of 5- and 4-fold electron-molecule configurations. A
superposition of 5- and 4-fold correlation functions is found to reproduce the
exact mixed symmetry pair correlation function to around 2%.Comment: 4 pages, 3 figure
Local level statistics for optical and transport properties of
  disordered systems at finite temperature

It is argued that the (traditional) global level statistics which determines
localization and coherent transport properties of disordered systems at zero
temperature (e.g. the Anderson model) becomes inappropriate when it comes to
incoherent transport. We define local level statistics which proves to be
relevant for finite temperature incoherent transport and optics of
one-dimensional systems (e.g. molecular aggregates, conjugated polymers, etc.).Comment: 4 pages, 2 figures, reported at EXCON'2006, to appear in the physica
  status solidi (c