298 research outputs found
Spin orientation by electric current in (110) quantum wells
We develop a theory of spin orientation by electric current in (110)-grown
semiconductor quantum wells. The controversy in the factor of two from two
existed approaches is resolved by pointing out the importance of energy
relaxation in this problem. The limiting cases of fast and slow energy
relaxation relative to spin relaxation are considered for asymmetric (110)
quantum wells. For symmetricly-doped structures the effect of spin orientation
is shown to exist due to spatial fluctuations of the Rashba spin-orbit
splitting. We demonstrate that the spin orientation depends strongly on the
correlation length of these fluctuations as well as on the ratio of the energy
and spin relaxation rates. The time-resolved kinetics of spin polarization by
electric current is also governed by the correlation length being not purely
exponential at slow energy relaxation. Electrical spin orientation in
two-dimensional topological insulators is calculated and compared with the spin
polarization induced by the magnetic field.Comment: 8 pages, 2 figure
Spin coherence of a two-dimensional electron gas induced by resonant excitation of trions and excitons in CdTe/(Cd,Mg)Te quantum wells
The mechanisms for generation of long-lived spin coherence in a
two-dimensional electron gas (2DEG) have been studied experimentally by means
of a picosecond pump-probe Kerr rotation technique. CdTe/(Cd,Mg)Te quantum
wells with a diluted 2DEG were investigated. The strong Coulomb interaction
between electrons and holes, which results in large binding energies of neutral
excitons and negatively charged excitons (trions), allows one to address
selectively the exciton or trion states by resonant optical excitation.
Different scenarios of spin coherence generation were analyzed theoretically,
among them the direct trion photocreation, the formation of trions from
photogenerated excitons and the electron-exciton exchange scattering. Good
agreement between experiment and theory is found.Comment: 18 pages, 20 figure
Magnetospheric response to the solar wind as indicated by the cross-polar potential drop and the low-latitude asymmetric disturbance field
International audienceThe cross-polar potential drop ?pc and the low-latitude asymmetric geomagnetic disturbance field, as indicated by the mid-latitude ASY-H magnetic index, are used to study the average magnetospheric response to the solar wind forcing for southward interplanetary magnetic field conditions. The state of the solar wind is monitored by the ACE spacecraft and the ionospheric convection is measured by the double probe electric field instrument on the Astrid-2 satellite. The solar wind-magnetosphere coupling is examined for 77 cases in February and from mid-May to mid-June 1999 by using the interplanetary magnetic field Bz component and the reconnection electric field. Our results show that the maximum correlation between ?pc and the reconnection electric field is obtained approximately 25 min after the solar wind has reached a distance of 11 RE from the Earth, which is the assumed average position of the magnetopause. The corresponding correlation for ASY-H shows two separate responses to the reconnection electric field, delayed by about 35 and 65 min, respectively. We suggest that the combination of the occurrence of a large magnetic storm on 18 February 1999 and the enhanced level of geomagnetic activity which peaks at Kp = 7- may explain the fast direct response of ASY-H to the solar wind at 35 min, as well as the lack of any clear secondary responses of ?pc to the driving solar wind at time delays longer than 25 min
Spin orientation of a two-dimensional electron gas by a high-frequency electric field
Coupling of spin states and space motion of conduction electrons due to
spin-orbit interaction opens up possibilities for manipulation of the electron
spins by electrical means. It is shown here that spin orientation of a
two-dimensional electron gas can be achieved by excitation of the carriers with
a linearly polarized high-frequency electric field. In (001)-grown quantum well
structures excitation with in-plane ac electric field induces orientation of
the electron spins along the quantum well normal, with the spin sign and the
magnitude depending on the field polarization.Comment: 5 pages, 1 figur
Magneto-gyrotropic effects in semiconductor quantum wells (review)
Magneto-gyrotropic photogalvanic effects in quantum wells are reviewed. We
discuss experimental data, results of phenomenological analysis and microscopic
models of these effects. The current flow is driven by spin-dependent
scattering in low-dimensional structures gyrotropic media resulted in asymmetry
of photoexcitation and relaxation processes. Several applications of the
effects are also considered.Comment: 28 pages, 13 figure
Quantum-dot-based optical polarization conversion
We report circular-to-linear and linear-to-circular conversion of optical
polarization by semiconductor quantum dots. The polarization conversion occurs
under continuous wave excitation in absence of any magnetic field. The effect
originates from quantum interference of linearly and circularly polarized
photon states, induced by the natural anisotropic shape of the self assembled
dots. The behavior can be qualitatively explained in terms of a pseudospin
formalism.Comment: 5 pages, 3 figures; a reference adde
Least action principle for envelope functions in abrupt heterostructures
We apply the envelope function approach to abrupt heterostructures starting
with the least action principle for the microscopic wave function. The
interface is treated nonperturbatively, and our approach is applicable to
mismatched heterostructure. We obtain the interface connection rules for the
multiband envelope function and the short-range interface terms which consist
of two physically distinct contributions. The first one depends only on the
structure of the interface, and the second one is completely determined by the
bulk parameters. We discover new structure inversion asymmetry terms and new
magnetic energy terms important in spintronic applications.Comment: 4 pages, 1 figur
Temperature dependence of polarization relaxation in semiconductor quantum dots
The decay time of the linear polarization degree of the luminescence in
strongly confined semiconductor quantum dots with asymmetrical shape is
calculated in the frame of second-order quasielastic interaction between
quantum dot charge carriers and LO phonons. The phonon bottleneck does not
prevent significantly the relaxation processes and the calculated decay times
can be of the order of a few tens picoseconds at temperature K,
consistent with recent experiments by Paillard et al. [Phys. Rev. Lett.
{\bf86}, 1634 (2001)].Comment: 4 pages, 4 figure
Anomalous in-plane magneto-optical anisotropy of self-assembled quantum dots
We report on a complex nontrivial behavior of the optical anisotropy of
quantum dots that is induced by a magnetic field in the plane of the sample. We
find that the optical axis either rotates in the opposite direction to that of
the magnetic field or remains fixed to a given crystalline direction. A
theoretical analysis based on the exciton pseudospin Hamiltonian unambiguously
demonstrates that these effects are induced by isotropic and anisotropic
contributions to the heavy-hole Zeeman term, respectively. The latter is shown
to be compensated by a built-in uniaxial anisotropy in a magnetic field B_c =
0.4 T, resulting in an optical response typical for symmetric quantum dots.Comment: 5 pages, 3 figure
Linear polarization of the photoluminescence of quantum wells
The degree and orientation of the magnetic-field induced linear polarization
of the photoluminescence from a wide range of heterostructures containing
(Cd,Mn)Te quantum wells between (Cd,Mn,Mg)Te barriers has been studied as a
function of detection photon energy, applied magnetic field strength and
orientation in the quantum well plane. A theoretical description of this effect
in terms of an in-plane deformation acting on the valence band states is
presented and is verified by comparison with the experimental data. We
attempted to identify clues to the microscopic origin of the valence band spin
anisotropy and to the mechanisms which actually determine the linear
polarization of the PL in the quantum wells subject to the in-plane magnetic
field. The conclusions of the present paper apply in full measure to
non-magnetic QWs as well as ensembles of disk-like QDs with shape and/or strain
anisotropy.Comment: 21 pages, 10 figure
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