551 research outputs found
Spin relaxation of conduction electrons in (110)-grown quantum wells
The theory of spin relaxation of conduction electrons is developed for
zinc-blende-type quantum wells grown on (110)-oriented substrate. It is shown
that, in asymmetric structures, the relaxation of electron spin initially
oriented along the growth direction is characterized by two different lifetimes
and leads to the appearance of an in-plane spin component. The magnitude and
sign of the in-plane component are determined by the structure inversion
asymmetry of the quantum well and can be tuned by the gate voltage. In an
external magnetic field, the interplay of cyclotron motion of carriers and the
Larmor precession of electron spin can result in a nonmonotonic dependence of
the spin density on the magnetic field.Comment: 5 pages, 3 figure
Optical properties of 1D photonic crystals based on multiple-quantum-well structures
A general approach to the analysis of optical properties of photonic crystals
based on multiple-quantum-well structures is developed. The effect of the
polarization state and a non-perpendicular incidence of the electromagnetic
wave is taken into account by introduction of an effective excitonic
susceptibility and an effective optical width of the quantum wells. This
approach is applied to consideration of optical properties of structures with a
pre-engineered break of the translational symmetry. It is shown, in particular,
that a layer with different exciton frequency placed at the middle of an MQW
structure leads to appearance of a resonance suppression of the reflection.Comment: 9 pages, 3 figures, submitted to PR
Non-Markovian spin relaxation in two-dimensional electron gas
We analyze by Monte-Carlo simulations and analytically spin dynamics of
two-dimensional electron gas (2DEG) interacting with short-range scatterers in
nonquantizing magnetic fields. It is shown that the spin dynamics is
non-Markovian with the exponential spin relaxation followed by the oscillating
tail due to the electrons residing on the closed trajectories. The tail relaxes
on a long time scale due to an additional smooth random potential and inelastic
processes. The developed analytical theory and Monte-Carlo simulations are in
the quantitative agreement with each other.Comment: 6 pages, 3 figure
Spin noise in quantum dot ensembles
We study theoretically spin fluctuations of resident electrons or holes in
singly charged quantum dots. The effects of external magnetic field and
effective fields caused by the interaction of electron and nuclei spins are
analyzed. The fluctuations of spin Faraday, Kerr and ellipticity signals
revealing the spin noise of resident charge carriers are calculated for the
continuous wave probing at the singlet trion resonance.Comment: 8 pages, 4 figure
Strong and weak coupling limits in optics of quantum well excitons
A transition between the strong (coherent) and weak (incoherent) coupling
limits of resonant interaction between quantum well (QW) excitons and bulk
photons is analyzed and quantified as a function of the incoherent damping rate
caused by exciton-phonon and exciton-exciton scattering. For confined QW
polaritons, a second, anomalous, damping-induced dispersion branch arises and
develops with increasing damping. In this case, the strong-weak coupling
transition is attributed to a critical damping rate, when the intersection of
the normal and damping-induced dispersion branches occurs. For the radiative
states of QW excitons, i.e., for radiative QW polaritons, the transition is
described as a qualitative change of the photoluminescence spectrum at grazing
angles along the QW structure. Furthermore, we show that the radiative
corrections to the QW exciton states with in-plane wavevector approaching the
photon cone are universally scaled by an energy parameter rather than diverge.
The strong-weak coupling transition rates are also proportional to the same
energy parameter. The numerical evaluations are given for a GaAs single quantum
well with realistic parameters.Comment: Published in Physical Review B. 29 pages, 12 figure
Properties of 1D two-barrier quantum pump with harmonically oscillating barriers
We study a one-dimensional quantum pump composed of two oscillating
delta-functional barriers. The linear and non-linear regimes are considered.
The harmonic signal applied to any or both barriers causes the stationary
current. The direction and value of the current depend on the frequency,
distance between barriers, value of stationary and oscillating parts of barrier
potential and the phase shift between alternating voltages.Comment: 7 pages, 8 figure
Theory of one-dimensional double-barrier quantum pump in two-frequency signal regime
A one-dimensional system with two -like barriers or wells
bi-chromaticaly oscillating at frequencies and is
considered. The alternating signal leads to the direct current across the
structure (even in a symmetric system). The properties of this quantum pump are
studied in a wide range of the system parameters.Comment: 4 pages, 5 figure
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