pinecone/core-2020-05-10-deduplication huggingface dataset:
Electronic and spin properties of hole point contacts

We have studied theoretically the effect of a tuneable lateral confinement on
two-dimensional hole systems realised in III-V semiconductor heterostructures.
Based on the 4x4 Luttinger description of the valence band, we have calculated
quasi-onedimensional (quasi-1D) hole subband energies and anisotropic Lande
g-factors. Confinement-induced band mixing results in the possibility to
manipulate electronic and spin properties of quasi-1D hole states over a much
wider range than is typically possible for confined conduction-band electrons.
Our results are relevant for recent experiments where source-drain-bias
spectroscopy was used to measure Zeeman splitting of holes in p-type quantum
point contacts.Comment: 4 pages, 3 figures, LaTex Wiley-VCH style (class files included),
  accepted for publication in proceedings of PASPS-I
Interlayer exchange coupling in (Ga,Mn)As based multilayers

Exhibiting antiferromagnetic interlayer coupling in dilute magnetic
semiconductor multilayers is essential for the realisation of
magnetoresistances analogous to giant magnetoresistance in metallic multilayer
structures. In this work we use a mean-field theory of carrier induced
ferromagnetism to explore possible (Ga,Mn)As based multilayer structures that
might yield antiferromagnetic coupling.Comment: 4 pages, 2 figures. To be published in physica status solidi c as the
  proceedings of the PASPS IV conferenc
Zeeman ratchets for ballistic spin currents

We investigate the possiblity of creating directed spin-polarized currents in
a two-dimensional electron gas (2DEG) subject to an asymmetric magnetic field
and an external adiabatic driving. We thereby generalize concepts of quantum
charge ratchets to the case with spin. Due to the Zeeman term in the
Hamiltonian, spin-up and -down electrons experience different effective
potentials, which can be tailored to achieve net spin currents without
corresponding charge currents. We consider ballistic, coherent transport in
waveguides defined in a 2DEG, where the magnetic field modulation is induced by
ferromagnetic stripes on top of the 2DEG.Comment: 4 pages, 4 figures, accepted for publication in physica status solidi
  (c) (2006
Spin densities in parabolic quantum wires with Rashba spin-orbit
  interaction

Using canonical transformations we diagonalize approximately the Hamiltonian
of a gaussian wire with Rashba spin-orbit interaction. This proceedure allows
us to obtain the energy dispersion relations and the wavefunctions with good
accuracy, even in systems with relatively strong Rashba coupling. With these
eigenstates one can calculate the non-equilibrium spin densities induced by
applying bias voltages across the sample. We focus on the $z$-component of the
spin density, which is related to the spin Hall effect.Comment: 4 pages, 4 figure
Ringlike structures in the density--magnetic-field $\rho_{xx}$ diagram
  of two-subband quantum Hall systems

Motivated by recent experiments [Zhang \textit{et al.}, Phys. Rev. Lett.
\textbf{95}, 216801 (2005) and Ellenberger \textit{et al.}, cond-mat/0602271]
reporting novel ringlike structures in the density--magnetic-field
($n_{2D}$\emph{--B}) diagrams of the longitudinal resistivity $\rho_{xx}$ of
quantum wells with two subbands, we investigate theoretically here the
magneto-transport properties of these quantum-Hall systems. We determine
$\rho_{xx}$ via both the Hartree and the Kohn-Sham self-consistent schemes plus
the Kubo formula. While the Hartree calculation yields diamond-shaped
structures in the $n_{2D}$\emph{--B} diagram, the calculation including
exchange and correlation effects (Kohn-Sham) more closely reproduces the
ringlike structures in the experiments.Comment: 4 pages, 1 figure (conference paper -- PASPS IV); v2: minor typos
  correcte
Strong spin relaxation length dependence on electric field gradients

We discuss the influence of electrical effects on spin transport, and in
particular the propagation and relaxation of spin polarized electrons in the
presence of inhomogeneous electric fields. We show that the spin relaxation
length strongly depends on electric field gradients, and that significant
suppression of electron spin polarization can occur as a result thereof. A
discussion in terms of a drift-diffusion picture, and self-consistent numerical
calculations based on a Boltzmann-Poisson approach shows that the spin
relaxation length in fact can be of the order of the charge screening length.Comment: 4 pages, 3 figures, to be presented at PASPSI
Peculiar Band Gap Structure of Graphene Nanoribbons

Graphene nanoribbons are quasi-one-dimensional meterials with finite width.
Characterizing a wide class of nanoribbons by edge shape and width, we make a
systematic analysis of their electronic properties. The band gap structure of
nanoribbons is shown to exhibit a valley structure with stream-like sequences
of metallic or almost metallic nanoribbons. Among them, all zigzag nanoribbons
are metallic, and armchair nanoribbons are metallic by period of 3. We find
that these stream-like sequences correspond to equi-width curves, and that the
band gap of chiral and armchair nanoribbons oscillate as a function of the
width. Furthermore a possible application of nanoribbons to nanoelectronics is
discussed.Comment: 8 pages, 7 figures: Presented at 14th International Conference on
  Superlattices, Nano-Structures and Nano-Devices, Istanbul, July 30-August 4
  (2006); Cover picture of the proceedin
Spin polarized and degenerate tunneling spectra in intrinsic Josephson junctions of Bi2212

International Conference on Superlattices, Nano-structures and Nano-devices, ICSNN-2006; Istanbul; Turkey; 30 July 2006 through 4 August 2006Tunneling characteristics of HgBr2 intercalated superconducting Bi2212 single crystals have been obtained by using 10×10 μm2 intrinsic Josephson junction stacks, so called mesa structures. The spin degenerate current is driven along the c-axis with Au layer using point contact tunneling assembly at 4,2 K. The spin polarized current is also driven along the c-axis of crystals with Au/Co/Au multilayer. In order to understand the role of ferromagnetic layer (Co), quasiparticle branches are examined with and without magnetic field. The magnetic field evolution of switching currents are obtained for gaining further insight about the spin injection through the stackTÜBİTAK TBAG-203
Microwave induced negative resistance states in 2D electron gas with
  periodic modulation

We study the microwave-induced photoconductivity of a two-dimensional
electron system (2DES) in the presence of a magnetic field and a
two-dimensional modulation. The microwave and Landau contributions are exactly
taken into account, while the periodic potential is treated perturbatively. The
longitudinal resistivity exhibits oscillations, periodic in $\omega /
\omega_c$. Negative resistance states (NRS) develop for sufficiently high
electron mobility and microwave power. This phenomenon appears in a narrow
window region of values of the lattice parameter ($a$), around $a \sim l_B$,
where $l_B$ is the magnetic length. It is proposed that these phenomena may be
observed in artificially fabricated arrays of periodic scatterers at the
interface of ultraclean heterostructures. {73.20.At,05.60.-k, 72.15.Rn}Comment: 3 pages, 1 figur
Thermoluminescence and optically stimulated luminescence of gamma-irradiated mineral zircon

Thermoluminescence (TL) manifested by gamma-irradiated mineral zircon has shown a strong TL peak at about 165 °C which is due to recombination of electrons and Dy3+ related shallow hole traps. After they have been removed by a short preheat we have observed two TL peaks at 300-320 °C and ≈420 °C, which are mainly due to recombination of electrons and Tb3+ related hole traps centres yielding its characteristic luminescence. The experimental results indicate that optically stimulated luminescence (OSL) is due to luminescent emission of Tb3+ ions and [SiO4]4– groups. The deep traps related to the 420 °C TL peak contribute to the Tb3+ related OSL. The deep traps related to the 300-320 °C TL peak contribute to OSL associated with the luminescent emission of [SiO4]4– groups.
Chemical vapour infiltration of nano-structured carbon in porous silicon

For the first time the results of the chemical vapor infiltration (CVI) of nanostructured sp(2) carbon in mesoporous silicon layers under process conditions normally used to grow diamond films by Hot Filament Chemical Vapour Deposition (HFCVD) are presented. The combined use of micro-Raman spectroscopy and Field Emission Gun Scanning Electron Microscopy (FEG-SEM) clearly demonstrated that disordered graphitic carbon was infiltrated in the PS pores, thus permeating completely the PS layer. Such a nanostructured carbon infiltration provided new properties to the PS material, which are potentially of great relevance for opto-electronics and sensors applications
New World of Gossamer Superconductivity

Since the discovery of the high-T$_{c}$ cuprate superconductor
La$_{2-x}$BaCuO$_{4}$ in 1986 by Bednorz and M\"{u}ller, controversy regarding
the nature or origin of this remarkable superconductivity has continued.
However, d-wave superconductivity in the hole-doped cuprates, arising due to
the anti-paramagnon exchange, was established around 1994. More recently we
have shown that the mean field theory, like the BCS theory of superconductivity
and Landau's Fermi liquid theory are adequate to describe the cuprates. The
keys for this development are the facts that a)the pseudogap phase is d-wave
density wave (dDW) and that the high-T$_{c}$ cuprate superconductivity is
gossamer (i.e. it exists in the presence of dDW).Comment: 6 pages, 4 figure
Electronic structure of zinc-blende MnTe within the GW approximation

Using the local spin-density approximation (LSDA) and the (non
self-consistent) GW approach, the (quasi-particle) band structure is calculated
for MnTe in zinc-blende geometry. Different parameters characterizing the
electronic structure are computed for an antiferromagnetic and the
ferromagnetic phase and compared with the experiment. The strong Hubbard-type
repulsion on the Mn-3d orbitals and the p-d hybridization are seen to be
responsible for substantial defects found in the LSDA picture. It is discussed
to which extent these can be improved upon by means of the GW approach.Comment: 9 pages, accepted for publication in pssc (special issue on II-VI
  semiconductors
Construction and purpose of effective field theories for frustrated
  magnetic order

This article reviews recent years' progress in the low temperature analysis
of standard models of spin glass order such as the Sherrington-Kirkpatrick (SK)
model. Applications to CdTe/CdMnTe layered systems and explanation of glassy
antiferromagnetic order at lowest temperatures stimulated us to study in detail
the beautifully complex physical effects of replica symmetry breaking (RSB).We
discuss analytical ideas based on highly precise numerical data which lead to
the construction of relatively simple effective field theories for the SK model
and help to understand the mysterious features of its exact solution. The goal
is to find construction principles for the theory of interplay between
frustrated magnetic order and various relevant physical degrees of freedom. The
emphasis in this article is on the role of Parisi's RSB, which surprisingly
creates critical phenomena in the low temperature limit despite the absence of
a standard phase transition.Comment: Published online in Physica Status Solidi C (June 4 2007
Interplay of the Rashba and Dresselhaus spin-orbit coupling in the
  optical spin susceptibility of 2D electron systems

We present calculations of the frequency-dependent spin susceptibility tensor
of a two-dimensional electron gas with competing Rashba and Dresselhaus
spin-orbit interaction. It is shown that the interplay between both types of
spin-orbit coupling gives rise to an anisotropic spectral behavior of the spin
density response function which is significantly different from that of
vanishing Rashba or Dresselhaus case. Strong resonances are developed in the
spin susceptibility as a consequence of the angular anisotropy of the energy
spin-splitting. This characteristic optical modulable response may be useful to
experimentally probe spin accumulation and spin density currents in such
systems
Coherence and Spatial Resolution of Transport in Quantum Cascade Lasers

The method of nonequilibrium Greens functions allows for a spatial and
energetical resolution of the electron current in Quantum Cascade Lasers. While
scattering does not change the spatial position of carriers, the entire spatial
evolution of charge can be attributed to coherent transport by complex wave
functions. We discuss the hierarchy of transport models and derive the density
matrix equations as well as the hopping model starting from the nonequilibrium
Greens functions approach.Comment: 6 pages, figures included, submitted to Proceedings of HCIS-15,
  physica status solidi (c
Evidence of the virtual Anderson transition in a narrow impurity band of
  p-GaAs/AlGaAs quantum wells: $\epsilon_4$ conductivity and electric breakdown
  at low temperatures

In highly doped uncompensated p-type layers within the central part of
GaAs/AlGaAs quantum wells at low temperatures we observed an activated behavior
of the conductivity with low activation energies (1-3) meV which can not be
ascribed to standard mechanisms. We attribute this behavior to the
delocalization of hole states near the maximum of the narrow impurity band in
the sense of the Anderson transition. Low temperature conduction $\epsilon_4$
is supported by an activation of minority carriers - electrons (resulting from
a weak compensation by back-ground defects) - from the Fermi level to the band
of delocalized states mentioned above. The corresponding behavior can be
specified as virtual Anderson transition. Low temperature transport ($<4$ K)
exhibits also strong nonlinearity of a breakdown type characterized in
particular by S-shaped I-V curve. The nonlinearity is observed in unexpectedly
low fields ($<10$ V/cm). Such a behavior can be explained by a simple model
implying an impact ionization of the localized states of the minority carriers
mentioned above to the band of Anderson-delocalized states.Comment: 9 pages, 6 fi
Electron-electron Relaxation in Disordered Interacting Systems

We study the relaxation of a non-equilibrium carrier distribution under the
influence of the electron-electron interaction in the presence of disorder.
Based on the Anderson model, our Hamiltonian is composed from a single particle
part including the disorder and a two-particle part accounting for the Coulomb
interaction. We apply the equation-of-motion approach for the density matrix,
which provides a fully microscopic description of the relaxation. Our results
show that the nonequlibrium distribution in this closed and internally
interacting system relaxes exponentially fast during the initial dynamics. This
fast relaxation can be described by a phenomenological damping rate. The total
single particle energy decreases in the redistribution process, keeping the
total energy of the system fixed. It turns out that the relaxation rate
decreases with increasing disorder.Comment: 4 pages, 3 figures, presented on "Transport in Interacting Disordered
  Systems 12" (TIDS 12) conferenc
Hopping transport of interacting carriers in disordered organic
  materials

Computer simulation of the hopping charge transport in disordered organic
materials has been carried out explicitly taking into account charge-charge
interactions. This approach provides a possibility to take into account dynamic
correlations that are neglected by more traditional approaches like mean field
theory. It was found that the effect of interaction is no less significant than
the usually considered effect of filling of deep states by non-interacting
carriers. It was found too that carrier mobility generally increases with the
increase of carrier density, but the effect of interaction is opposite for two
models of disordered organic materials: for the non-correlated random
distribution of energies with Gaussian DOS mobility decreases with the increase
of the interaction strength, while for the model with long range correlated
disorder mobility increases with the increase of interaction strength.Comment: 6 pages, 5 figures, extended version from the conference TIDS1
Effect of matrix parameters on mesoporous matrix based quantum
  computation

We present a solid state implementation of quantum computation, which
improves previously proposed optically driven schemes. Our proposal is based on
vertical arrays of quantum dots embedded in a mesoporous material which can be
fabricated with present technology. We study the feasibility of performing
quantum computation with different mesoporous matrices. We analyse which matrix
materials ensure that each individual stack of quantum dots can be considered
isolated from the rest of the ensemble-a key requirement of our scheme. This
requirement is satisfied for all matrix materials for feasible structure
parameters and GaN/AlN based quantum dots. We also show that one dimensional
ensembles substantially improve performances, even of CdSe/CdS based quantum
dots
Optical absorption in ZrO2–x-C nanocomposite films on polymer substrates: application of an effective medium theory

International audienceRF sputtering from separate zirconia and graphite targets enables room-temperature co-deposition of ZrO2–x and carbon onto polycarbonate substrates. Films consist of amorphous carbon dispersed in tetragonal nanocrystalline zirconia; their optical properties have been determined by reflectance measurements at normal incidence and over the visible range. The optical constants of each component of the composite have been extracted; the experimental reflectance spectra have been fitted to Maxwell-Garnett effective medium theory, leading to the effective dielectric constants of the film. Absorption is characterized by the band gap, the energy and lifetime of the optical transition of the absorbing carbon phase. These parameters are deduced from the imaginary part of the dielectric function using Tauc-Lorentz model (TL) and from the extinction coefficient using Forouhi-Bloomer model (FB) in which an energy dependence of the matrix element of the transition has been introduced. Furthermore, the energies of the peak transition and the maximum of the extinction coefficient are so similar that they prove the self-consistency of the modified-FB model applied to the amorphous carbon phase of the composite films
Enhanced co-solubilities of Ca and Si in YAG (Y3Al5O12)

General garnet structure (Ia3-d) is a forgiving host and can accommodate cations of varying sizes and valence states. Studies on highly yttrium doped alumina ceramics with Ca and Si contamination indicated that YAG precipitates in the ceramic had a propensity to allow simultaneous incorporation of small amounts of Ca and Si impurities in their structure. In this study, using chemical synthesis techniques it was shown that YAG can accommodate up to approximately 8 cation % Ca+2 and Si+4 (i.e. Ca+2/Y+3 and Si+4/Y+3) if they are incorporated together. Equilibrium conditions are established by calcining samples at 900 C for 2 hours and cooling the samples to room temperature in the furnace. Disappearing-phase method and energy dispersive X-ray spectroscopy (EDS) were used to determine solubility and co-solubility limits. Beyond the solubility limit phase separation occurred and three crystalline yttrium aluminate phases (YAG, YAP (yttrium aluminate perovskite, YAlO3), YAM (yttrium aluminate monoclinic, Y4Al2O9)) were observed. It is believed that the excess Ca and Si above co-solubility limit precipitate out in the form of an x-ray amorphous anorthite-like glass in the system
Temperature-dependent High-Frequency Performance of Deep Submicron Ion-Implanted AlGaN/GaN HEMTs

A study of the low temperature DC and RF performance of deep submicron AlGaN/GaN high electron mobility transistors (HEMTs) is reported. From 300 K to 100 K both extrinsic transconductance and drain current increase by  30%, mainly due to the lowering of the optical phonon scattering that allows higher electron mobility. Source and drain resistances improve too, which contributes to the 15-20% increase of ft and fmax. The low temperature small signal model has also been extracted accurately at every 50 K. Inductances and capacitances remain constant in the range of temperatures measured. The intrinsic transconductance can be also considered temperature independent, but the output conductance decreases from 300 K to 100 K indicating a better confinement of the 2DEG. The HEMT performance obtained at 100 K can be reached at room temperature by reducing the parasitic resistances and improving the GaN buffer isolation
Rapid energy transfer and its temperature dependence in π-conjugated dendrimers

We investigate a rapid energy transfer (ET) process and its temperature dependence in a star-shaped stilbenoid phthalocyanine
(SSS1Pc) dendrimer having π-conjugated light-harvesting (LH) antennas. In SSS1Pc, intense corephotoluminescence
is observed under selective excitation on the LH-antenna as a result of the highly efficient ET
from the LH-antenna. Pump-probe experiments show that ET occurs rapidly with a rising time constant (∼ 250 fs).
To understand such rapid ET, we employ a simplified ET model through a π-conjugated network between the LHantenna
and the core that takes into account the steric hindrance between the LH-antenna subunits. Our model reveals
that the highly efficient ET at room temperature in SSS1Pc takes place through the π-conjugated network mediated by
a thermally activated torsional vibration of the aromatic ring subgroup in the LH-antenna
Engineering molecular aggregate spectra

We show that optical properties of linear molecular aggregates undergo
drastic changes when aggregates are deposited on a metal surface. The
dipole-dipole interactions of monomers with their images can result in strong
{re-structuring of both the exciton band and the absorption spectrum, depending
on the arrangement of the monomer transition dipoles with respect to the
surface.Comment: 4 two-column pages, Proceedings of the 8th International Conference
  on Excitonic Processes in Condensed Matter, June 22-27, Kyoto, Japa
Synthesis, characterization, and its PL dynamics of colloidal type II CdTe/CdSe nanocrystals

We describe our improved synthesis and optical properties of high quality type II CdTe/CdSe nanocrystals (NCs). Specifically, clear shell-thickness dependences have been observed in the absorption and photoluminescence (PL) spectra and PL decay profiles as well. The magnitude of the lowest absorption band decreases drastically with large redshift as the shell thickness increases. The origin will be discussed on the bases of the model where the spatial configuration of the lowest electron-hole pair in the NCs changes from that of type I to type II as the shell thickness increases. As for the PL lifetime of the lowest electron-hole excitations, substantial increase is observed with increasing shell thickness. This can also be understood by considering the spatial configuration; spatial overlap between electron and hole wavefunctions decreases with increasing shell thickness, thus the lifetime increases. As for the NCs with extremely thin shell (∼1 ML; 1 ML = 0.35 nm), the PL lifetime seems much longer than expected. This suggests that the thin shells seem imperfect and work rather a kind of trap sites than layers