2,872 research outputs found
Kinetics of spin coherence of electrons in -type InAs quantum wells under intense terahertz laser fields
Spin kinetics in -type InAs quantum wells under intense terahertz laser
fields is investigated by developing fully microscopic kinetic spin Bloch
equations via the Floquet-Markov theory and the nonequilibrium Green's function
approach, with all the relevant scattering, such as the electron-impurity,
electron-phonon, and electron-electron Coulomb scattering explicitly included.
We find that a {\em finite} steady-state terahertz spin polarization induced by
the terahertz laser field, first predicted by Cheng and Wu [Appl. Phys. Lett.
{\bf 86}, 032107 (2005)] in the absence of dissipation, exists even in the
presence of all the scattering. We further discuss the effects of the terahertz
laser fields on the spin relaxation and the steady-state spin polarization. It
is found that the terahertz laser fields can {\em strongly} affect the spin
relaxation via hot-electron effect and the terahertz-field-induced effective
magnetic field in the presence of spin-orbit coupling. The two effects compete
with each other, giving rise to {\em non-monotonic} dependence of the spin
relaxation time as well as the amplitude of the steady state spin polarization
on the terahertz field strength and frequency. The terahertz field dependences
of these quantities are investigated for various impurity densities, lattice
temperatures, and strengths of the spin-orbit coupling. Finally, the importance
of the electron-electron Coulomb scattering on spin kinetics is also addressed.Comment: 17 pages, 16 figures, Phys. Rev. B 78, 2008, in pres
Spin relaxation due to random Rashba spin-orbit coupling in GaAs (110) quantum wells
We investigate the spin relaxation due to the random Rashba spin-orbit
coupling in symmetric GaAs (110) quantum wells from the fully microscopic
kinetic spin Bloch equation approach. All relevant scatterings, such as the
electron-impurity, electron--longitudinal-optical-phonon,
electron--acoustic-phonon, as well as electron-electron Coulomb scatterings are
explicitly included. It is shown that our calculation reproduces the
experimental data by M\"uller {\em et al.} [Phys. Rev. Lett. {\bf 101}, 206601
(2008)] for a reasonable choice of parameter values. We also predict that the
temperature dependence of spin relaxation time presents a peak in the case with
low impurity density, which originates from the electron-electron Coulomb
scattering.Comment: 5 pages, 2 figures, EPL in pres
Fine structure of exciton excited levels in a quantum dot with a magnetic ion
The fine structure of excited excitonic states in a quantum dot with an
embedded magnetic ion is studied theoretically and experimentally. The
developed theory takes into account the Coulomb interaction between charged
carriers, the anisotropic long-range electron-hole exchange interaction in the
zero-dimensional exciton, and the exchange interaction of the electron and the
hole with the -electrons of a Mn ion inserted inside the dot. Depending on
the relation between the quantum dot anisotropy and the exciton-Mn coupling the
photoluminescence excitation spectrum has a qualitatively different behavior.
It provides a deep insight into the spin structure of the excited excitonic
states.Comment: 6 pages, 6 figure
Effect of electron-electron scattering on spin dephasing in a high-mobility low-density twodimensional electron gas
Utilizing time-resolved Kerr rotation techniques, we have investigated the
spin dynamics of a high mobility, low density two dimensional electron gas in a
GaAs/Al0:35Ga0:65As heterostructure in dependence on temperature from 1.5 K to
30 K. It is found that the spin relaxation/dephasing time under a magnetic
field of 0.5 T exhibits a maximum of 3.12 ns around 14 K, superimposed on an
increasing background with rising temperature. The appearance of the maximum is
ascribed to that at the temperature where the crossover from the degenerate to
the nondegenerate regime takes place, electron-electron Coulomb scattering
becomes strongest, and thus inhomogeneous precession broadening due to
D'yakonov-Perel'(DP) mechanism becomes weakest. These results agree with the
recent theoretical predictions [Zhou et al., PRB 75, 045305 (2007)], verifying
the importance of electron-electron Coulomb scattering to electron spin
relaxation/dephasing.Comment: 4 pages, 2 figure
QED calculation of the 2p1/2-2s and 2p3/2-2s transition energies and the ground-state hyperfine splitting in lithiumlike scandium
We present the most accurate up-to-date theoretical values of the
{2p_{1/2}}-{2s} and {2p_{3/2}}-{2s} transition energies and the ground-state
hyperfine splitting in . All two- and three-electron
contributions to the energy values up to the two-photon level are treated in
the framework of bound-state QED without \aZ-expansion. The interelectronic
interaction beyond the two-photon level is taken into account by means of the
large-scale configuration-interaction Dirac-Fock-Sturm (CI-DFS) method. The
relativistic recoil correction is calculated with many-electron wave functions
in order to take into account the electron-correlation effect. The accuracy of
the transition energy values is improved by a factor of five compared to the
previous calculations. The CI-DFS calculation of interelectronic-interaction
effects and the evaluation of the QED correction in an effective screening
potential provide significant improvement for the hyperfine splitting. The
results obtained are in a good agreement with recently published experimental
data.Comment: 10 pages, 2 table
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
Total Angular Momentum Conservation During Tunnelling through Semiconductor Barriers
We have investigated the electrical transport through strained
p-Si/Si_{1-x}Ge_x double-barrier resonant tunnelling diodes. The confinement
shift for diodes with different well width, the shift due to a central
potential spike in a well, and magnetotunnelling spectroscopy demonstrate that
the first two resonances are due to tunnelling through heavy hole levels,
whereas there is no sign of tunnelling through the first light hole state. This
demonstrates for the first time the conservation of the total angular momentum
in valence band resonant tunnelling. It is also shown that conduction through
light hole states is possible in many structures due to tunnelling of carriers
from bulk emitter states.Comment: 4 pages, 4 figure
Pure spin photocurrents in low-dimensional structures
As is well known the absorption of circularly polarized light in
semiconductors results in optical orientation of electron spins and
helicity-dependent electric photocurrent, and the absorption of linearly
polarized light is accompanied by optical alignment of electron momenta. Here
we show that the absorption of unpolarized light leads to generation of a pure
spin current, although both the average electron spin and electric current
vanish. We demonstrate this for direct interband and intersubband as well as
indirect intraband (Drude-like) optical transitions in semiconductor quantum
wells (QWs).Comment: 4 pages, 3 figure
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