379 research outputs found
Exciton spin decay modified by strong electron-hole exchange interaction
We study exciton spin decay in the regime of strong electron-hole exchange
interaction. In this regime the electron spin precession is restricted within a
sector formed by the external magnetic field and the effective exchange fields
triggered by random spin flips of the hole. Using Hanle effect measurements, we
demonstrate that this mechanism dominates our experiments in CdTe/(Cd,Mg)Te
quantum wells. The calculations provide a consistent description of the
experimental results, which is supported by independent measurements of the
parameters entering the model.Comment: 5 pages, 3 figure
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
Optical Spin Orientation in Strained Superlattices
Optical orientation in the strained semiconductor superlattices is
investigated theoretically. The dependence of the features in spin-polarization
spectra on the structure parameters is clarified. The value of polarization in
the first polarization maximum in the SL structures is shown to grow with the
splitting between the hh- and lh- states of the valence band, the joint strain
and confinement effects on the hh1- lh1 splitting being strongly influenced by
the tunneling in the barriers. In strained structures with high barriers for
the holes initial polarization can exceed 95 %. Calculated polarization spectra
are close to the experimental spectra of polarized electron emission.Comment: 20 pages, 8 figure
Polariton Dispersion Law in Periodic Bragg and Near-Bragg Multiple Quantum Well Structures
The structure of polariton spectrum is analyzed for periodic multiple quantum
well structures with periods at or close to Bragg resonance condition at the
wavelength of the exciton resonance. The results obtained used to discuss
recent reflection and luminescent experiments by M. H\"{u}bner et al [Phys.
Rev. Lett. {\bf 83}, 2841 (1999)] carried out with long multiple quantum well
structures. It is argued that the discussion of quantum well structures with
large number of wells is more appropriate in terms of normal modes of infinite
periodic structures rather then in terms of super- and sub- radiant modes.Comment: replaced with a new version, an error in one of the equations is
correcte
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
Influence of Anomalous Dispersion on Optical Characteristics of Quantum Wells
Frequency dependencies of optical characteristics (reflection, transmission
and absorption of light) of a quantum well are investigated in a vicinity of
interband resonant transitions in a case of two closely located excited energy
levels. A wide quantum well in a quantizing magnetic field directed normally to
the quantum-well plane, and monochromatic stimulating light are considered.
Distinctions between refraction coefficients of barriers and quantum well, and
a spatial dispersion of the light wave are taken into account. It is shown that
at large radiative lifetimes of excited states in comparison with nonradiative
lifetimes, the frequency dependence of the light reflection coefficient in the
vicinity of resonant interband transitions is defined basically by a curve,
similar to the curve of the anomalous dispersion of the refraction coefficient.
The contribution of this curve weakens at alignment of radiative and
nonradiative times, it is practically imperceptible at opposite ratio of
lifetimes . It is shown also that the frequency dependencies similar to the
anomalous dispersion do not arise in transmission and absorption coefficients.Comment: 10 pages, 6 figure
Non-exponential spin relaxation in magnetic field in quantum wells with random spin-orbit coupling
We investigate the spin dynamics of electrons in quantum wells where the
Rashba type of spin-orbit coupling is present in the form of random nanosize
domains. We study the effect of magnetic field on the spin relaxation in these
systems and show that the spatial randomness of spin-orbit coupling limits the
minimum relaxation rate and leads to a Gaussian time-decay of spin polarization
due to memory effects. In this case the relaxation becomes faster with increase
of the magnetic field in contrast to the well known magnetic field suppression
of spin relaxation.Comment: published version, minor change
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
Spin Hall Effect
The intrinsic spin Hall effect in semiconductors has developed to a
remarkably lively and rapidly growing branch of research in the field of
semiconductor spintronics. In this article we give a pedagogical overview on
both theoretical and experimental accomplishments and challenges. Emphasis is
put on the the description of the intrinsic mechanisms of spin Hall transport
in III-V zinc-blende semiconductors, and on the effects of dissipation.Comment: 22 pages, minor adjustments, version as publishe
Spin noise spectroscopy of a single-quantum-well microcavity
We report on the first experimental observation of spin noise in a single
semiconductor quantum well embedded into a microcavity. The great
cavity-enhanced sensitivity to fluctuations of optical anisotropy has allowed
us to measure the Kerr rotation and ellipticity noise spectra in the strong
coupling regime. The spin noise spectra clearly show two resonant features: a
conventional magneto-resonant component shifting towards higher frequencies
with magnetic field and an unusual "nonmagnetic" component centered at zero
frequency and getting suppressed with increasing magnetic field. We attribute
the first of them to the Larmor precession of free electron spins, while the
second one being presumably due to hyperfine electron-nuclei spin interactions.Comment: 5 pages, 6 figures + supplement (4 pages, 1 figure
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