92 research outputs found
Elementary electronic excitation from a two-dimensional hole gas in the presence of spin-orbit interaction
We present a theoretical study of the elementary electronic excitation
associated with plasmon modes in a two-dimensional hole gas (2DHG) in the
presence of spin-orbit (SO) interaction induced by the Rashba effect. The
calculation is carried out using a standard random-phase-approximation
approach. It is found that in such a spintronic system, plasmon excitation can
be achieved via intra- and inter-SO electronic transitions around the Fermi
level. As a result, the intra- and inter-SO plasmon modes can be observed. More
importantly, the plasmon modes induced by inter-SO transition are optic-like
and these modes can be directly applied to identify the Rashba spin splitting
in 2DHG systems through optical measurements. The interesting features of the
plasmon excitation in a spin split 2DHG are analyzed and discussed in details.
Moreover, the results obtained for a 2DHG are compared with those obtained for
a spin-splitting 2DEG reported very recently.Comment: 17 pages and 6 figure
Plasmons in coupled bilayer structures
We calculate the collective charge density excitation dispersion and spectral
weight in bilayer semiconductor structures {\it including effects of interlayer
tunneling}. The out-of-phase plasmon mode (the ``acoustic'' plasmon) develops a
long wavelength gap in the presence of tunneling with the gap being
proportional to the square root (linear power) of the tunneling amplitude in
the weak (strong) tunneling limit. The in-phase plasmon mode is qualitatively
unaffected by tunneling. The predicted plasmon gap should be a useful tool for
studying many-body effects.Comment: 10 pages, 6 figures. to appear in Phys. Rev. Let
Pressure Dependence of Born Effective Charges, Dielectric Constant and Lattice Dynamics in SiC
The pressure dependence of the Born effective charge, dielectric constant and
zone-center LO and TO phonons have been determined for -SiC by a linear
response method based on the linearized augmented plane wave calculations
within the local density approximation. The Born effective charges are found to
increase nearly linearly with decreasing volume down to the smallest volume
studied, , corresponding to a pressure of about 0.8 Mbar. This
seems to be in contradiction with the conclusion of the turnover behavior
recently reported by Liu and Vohra [Phys.\ Rev.\ Lett.\ {\bf 72}, 4105 (1994)]
for -SiC. Reanalyzing their procedure to extract the pressure dependence of
the Born effective charges, we suggest that the turnover behavior they obtained
is due to approximations in the assumed pressure dependence of the dielectric
constant , the use of a singular set of experimental data
for the equation of state, and the uncertainty in measured phonon frequencies,
especially at high pressure.Comment: 25 pages, revtex, 5 postscript figures appended, to be published in
Phys. Rev.
Dynamical-charge neutrality at a crystal surface
For both molecules and periodic solids, the ionic dynamical charge tensors
which govern the infrared activity are known to obey a dynamical neutrality
condition. This condition enforces their sum to vanish (over the whole finite
system, or over the crystal cell, respectively). We extend this sum rule to the
non trivial case of the surface of a semiinfinite solid and show that, in the
case of a polar surface of an insulator, the surface ions cannot have the same
dynamical charges as in the bulk. The sum rule is demonstrated through
calculations for the Si-terminated SiC(001) surface.Comment: 4 pages, latex file, 1 postscript figure automatically include
Dielectric Properties of the Quasi-Two-Dimensional Electron Liquid in Heterojunctions
A quasi-two-dimensional (Q2D) electron liquid (EL) is formed at the interface
of a semiconductor heterojunction. For an accurate characterization of the Q2D
EL, many-body effects need to be taken into account beyond the random phase
approximation. In this theoretical work, the self-consistent static local-field
correction known as STLS is applied for the analysis of the Q2D EL. The
penetration of the charge distribution to the barrier-acting material is taken
into consideration through a variational approach. The Coulomb from factor that
describes the effective 2D interaction is rigorously treated. The longitudinal
dielectric function and the plasmon dispersion of the Q2D EL are presented for
a wide range of electron and ionized acceptor densities choosing GaAs/AlGaAs as
the physical system. Analytical expressions fitted to our results are also
supplied to enable a widespread use of these results.Comment: 39 pages (in LaTeX), including 8 PostScript figure
Surface plasmons in metallic structures
Since the concept of a surface collective excitation was first introduced by
Ritchie, surface plasmons have played a significant role in a variety of areas
of fundamental and applied research, from surface dynamics to surface-plasmon
microscopy, surface-plasmon resonance technology, and a wide range of photonic
applications. Here we review the basic concepts underlying the existence of
surface plasmons in metallic structures, and introduce a new low-energy surface
collective excitation that has been recently predicted to exist.Comment: 14 pages, 14 figures, to appear in J. Opt. A: Pure Appl. Op
Many-body correlations probed by plasmon-enhanced drag measurements in double quantum well structures
Electron drag measurements of electron-electron scattering rates performed
close to the Fermi temperature are reported. While evidence of an enhancement
due to plasmons, as was recently predicted [K. Flensberg and B. Y.-K. Hu, Phys.
Rev. Lett. 73, 3572 (1994)], is found, important differences with the
random-phase approximation based calculations are observed. Although static
correlation effects likely account for part of this difference, it is argued
that correlation-induced multiparticle excitations must be included to account
for the magnitude of the rates and observed density dependences.Comment: 4 pages, 3 figures, revtex Accepted in Phys. Rev.
Carrier relaxation due to electron-electron interaction in coupled double quantum well structures
We calculate the electron-electron interaction induced energy-dependent
inelastic carrier relaxation rate in doped semiconductor coupled double quantum
well nanostructures within the two subband approximation at zero temperature.
In particular, we calculate, using many-body theory, the imaginary part of the
full self-energy matrix by expanding in the dynamically RPA screened Coulomb
interaction, obtaining the intrasubband and intersubband electron relaxation
rates in the ground and excited subbands as a function of electron energy. We
separate out the single particle and the collective excitation contributions,
and comment on the effects of structural asymmetry in the quantum well on the
relaxation rate. Effects of dynamical screening and Fermi statistics are
automatically included in our many body formalism rather than being
incorporated in an ad-hoc manner as one must do in the Boltzman theory.Comment: 26 pages, 5 figure
A convenient band-gap interpolation technique and an improved band line-up model for InGaAlAs on InP
The band-gap energy and the band line-up of InGaAlAs quaternary compound material on InP are essential information for the theoretical study of physical properties and the design of optoelectronics devices operating in the long-wavelength communication window. The band-gap interpolation of In1-x-y Ga (x) Al (y) As on InP is known to be a challenging task due to the observed discrepancy of experimental results arising from the bowing effect. Besides, the band line-up results of In1-x-y Ga (x) Al (y) As on InP based on previously reported models have limited success by far. In this work, we propose an interpolation solution using the single-variable surface bowing estimation interpolation method for the fitting of experimentally measured In1-x-y Ga (x) Al (y) As band-gap data with various degree of bowing using the same set of input parameters. The suggested solution provides an easier and more physically interpretable way to determine not only lattice matched, but also strained band-gap energy of In1-x-y Ga (x) Al (y) As on InP based on the experimental results. Interpolated results from this convenient method show a more favourable match to multiple independent experiment data sets measured under different temperature conditions as compared to those obtained from the commonly used weighted-sum approach. On top of that, extended framework of the model-solid theory for the band line-up of In1-x-y Ga (x) Al (y) As/InP heterostructure is proposed. Our model-solid theory band line-up result using the proposed extended framework has shown an improved accuracy over those without the extension. In contrast to some previously reported works, it is worth noting that the band line-up result based on our proposed extended model-solid theory has also shown to be more accurate than those given by Harrison's mode
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