730 research outputs found
Ab initio many-body calculation of excitons in solid Ne and Ar
Absorption spectra, exciton energy levels and wave functions for solid Ne and
Ar have been calculated from first principles using many-body techniques.
Electronic band structures of Ne and Ar were calculated using the GW
approximation. Exciton states were calculated by diagonalizing an exciton
Hamiltonian derived from the particle-hole Green function, whose equation of
motion is the Bethe-Salpeter equation. Singlet and triplet exciton series up to
n=5 for Ne and n=3 for Ar were obtained. Binding energies and
longitudinal-transverse splittings of n=1 excitons are in excellent agreement
with experiment. Plots of correlated electron-hole wave functions show that the
electron-hole complex is delocalised over roughly 7 a.u. in solid Ar.Comment: 6 page
Experimental Separation of Rashba and Dresselhaus Spin-Splittings in Semiconductor Quantum Wells
The relative strengths of Rashba and Dresselhaus terms describing the
spin-orbit coupling in semiconductor quantum well (QW) structures are extracted
from photocurrent measurements on n-type InAs QWs containing a two-dimensional
electron gas (2DEG). This novel technique makes use of the angular distribution
of the spin-galvanic effect at certain directions of spin orientation in the
plane of a QW. The ratio of the relevant Rashba and Dresselhaus coefficients
can be deduced directly from experiment and does not relay on theoretically
obtained quantities. Thus our experiments open a new way to determine the
different contributions to spin-orbit coupling
Electron and Hole Spin Splitting and Photogalvanic Effect in Quantum Wells
A theory of the circular photogalvanic effect caused by spin splitting in
quantum wells is developed. Direct interband transitions between the hole and
electron size-quantized subbands are considered. It is shown that the
photocurrent value and direction depend strongly on the form of the spin-orbit
interaction. The currents induced by structure-, bulk-, and interface-inversion
asymmetry are investigated. The photocurrent excitation spectra caused by spin
splittings in both conduction and valence bands are calculated.Comment: 7 pages, 3 figure
Generation of Intrinsic Vibrational Gap Modes in Three-Dimensional Ionic Crystals
The existence of anharmonic localization of lattice vibrations in a perfect
3-D diatomic ionic crystal is established for the rigid-ion model by molecular
dynamics simulations. For a realistic set of NaI potential parameters, an
intrinsic localized gap mode vibrating in the [111] direction is observed for
fcc and zinc blende lattices. An axial elastic distortion is an integral
feature of this mode which forms more readily for the zinc blende than for the
fcc structure. Molecular dynamics simulations verify that in each structure
this localized mode may be stable for at least 200 cycles.Comment: 5 pages, 4 figures, RevTeX, using epsf.sty. To be published in Phys.
Rev. B. Also available at http://www.msc.cornell.edu/~kiselev
Optical creation of vibrational intrinsic localized modes in anharmonic lattices with realistic interatomic potentials
Using an efficient optimal control scheme to determine the exciting fields,
we theoretically demonstrate the optical creation of vibrational intrinsic
localized modes (ILMs) in anharmonic perfect lattices with realistic
interatomic potentials. For systems with finite size, we show that ILMs can be
excited directly by applying a sequence of femtosecond visible laser pulses at
THz repetition rates. For periodic lattices, ILMs can be created indirectly via
decay of an unstable extended lattice mode which is excited optically either by
a sequence of pulses as described above or by a single picosecond far-infrared
laser pulse with linearly chirped frequency. In light of recent advances in
experimental laser pulse shaping capabilities, the approach is experimentally
promising.Comment: 20 pages, 7 eps figures. Accepted, Phys. Rev.
Transport Properties of Clean Quantum Point Contacts
Quantum point contacts are fundamental building blocks for mesoscopic
transport experiments and play an important role in recent interference- and
fractional quantum Hall experiments. However, it is not clear how
electron-electron interactions and the random disorder potential influence the
confinement potential and give rise to phenomena like the mysterious 0.7
anomaly. Novel growth techniques of GaAs/AlGaAs heterostructures for
high-mobility two-dimensional electron gases enable us to investigate quantum
point contacts with a strongly suppressed disorder potential. These clean
quantum point contacts indeed show transport features that are obscured by
disorder in standard samples. From this transport data, we are able to extract
the parameters of the confinement potential which describe its shape in
longitudinal and transverse direction. Knowing the shape (and hence the slope)
of the confinement potential might be crucial to predict which
interaction-induced states can form in quantum point contacts
Chaos and Synchronized Chaos in an Earthquake Model
We show that chaos is present in the symmetric two-block Burridge-Knopoff
model for earthquakes. This is in contrast with previous numerical studies, but
in agreement with experimental results. In this system, we have found a rich
dynamical behavior with an unusual route to chaos. In the three-block system,
we see the appearance of synchronized chaos, showing that this concept can have
potential applications in the field of seismology.Comment: To appear in Physical Review Letters (13 pages, 6 figures
Temperature dependence of D'yakonov-Perel' spin relaxation in zinc blende semiconductor quantum structures
The D'yakonov-Perel' mechanism, intimately related to the spin splitting of
the electronic states, usually dominates the spin relaxation in zinc blende
semiconductor quantum structures. Previously it has been formulated for the two
limiting cases of low and high temperatures. Here we extend the theory to give
an accurate description of the intermediate regime which is often relevant for
room temperature experiments. Employing the self-consistent multiband envelope
function approach, we determine the spin splitting of electron subbands in
n-(001) zinc blende semiconductor quantum structures. Using these results we
calculate spin relaxation rates as a function of temperature and obtain
excellent agreement with experimental data.Comment: 9 pages, 4 figure
Spin Orientation of Holes in Quantum Wells
This paper reviews the spin orientation of spin-3/2 holes in quantum wells.
We discuss the Zeeman and Rashba spin splitting in hole systems that are
qualitatively different from their counterparts in electron systems. We show
how a systematic understanding of the unusual spin-dependent phenomena in hole
systems can be gained using a multipole expansion of the spin density matrix.
As an example we discuss spin precession in hole systems that can give rise to
an alternating spin polarization. Finally, we discuss the qualitatively
different regimes of hole spin polarization decay in clean and dirty samples.Comment: 14 pages, 8 figure
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