806 research outputs found
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
Resonant Fibonacci Quantum Well Structures
We propose a resonant one-dimensional quasicrystal, namely, a multiple
quantum well (MQW) structure satisfying the Fibonacci-chain rule with the
golden ratio between the long and short inter-well distances. The resonant
Bragg condition is generalized from the periodic to Fibonacci MQWs. A
dispersion equation for exciton-polaritons is derived in the two-wave
approximation, the effective allowed and forbidden bands are found. The
reflection spectra from the proposed structures are calculated as a function of
the well number and detuning from the Bragg condition.Comment: 5 pages, 3 figures, submitted to Phys. Rev.
Electron scattering in quantum wells subjected to an in-plane magnetic field
It is shown that the electron scattering by static defects, acoustic or
optical phonons in quantum wells subjected to an in-plane magnetic field is
asymmetric. The probability of scattering contains terms which are proportional
to both the electron wave vector and the magnetic field components. The terms
under study are caused by the lack of an inversion center in quantum wells due
to structure or bulk inversion asymmetry although they are of pure diamagnetic
origin. Such a magnetic field induced asymmetry of scattering can be
responsible for a number of phenomena. In particular, the asymmetry of
inelastic electron-phonon interaction leads to an electric current flow if only
the electron gas is driven out of thermal equilibrium with the crystal lattice.Comment: 5 pages, 1 figur
Spin orientation of two-dimensional electron gas under intraband optical pumping
The theory of spin orientation of two-dimensional (2D) electron gas has been
developed for intrasubband indirect optical transitions. The monopolar optical
orientation of electrons in the conduction band is caused by the indirect
scattering with virtual intermediate states in the valence band and allowance
for selection rules for interband transitions. The considered mechanism of
optical orientation is shown to be in an inherent relation with the special
Elliot-Yafet mechanism of electron spin relaxation induced by virtual interband
scattering.Comment: 3 pages, 2 figures, Symposium "Nanostructures: Physics and
Technology", St.Petersburg, Russia, 200
Influence of bottom topography on integral constraints in zonal flows with parameterized potential vorticity fluxes
An integral constraint for eddy fluxes of potential vorticity (PV), corresponding to global momentum conservation, is applied to two-layer zonal quasi-geostrophic channel flow. This constraint must be satisfied for any type of parameterization of eddy PV fluxes. Bottom topography strongly influence the integral constraint compared to a flat bottom channel. An analytical solution for the mean flow solution has been found by using asymptotic expansion in a small parameter which is the ratio of the Rossby radius to the meridional extent of the channel. Applying the integral constraint to this solution, one can find restrictions for eddy PV transfer coefficients which relate the eddy fluxes of PV to the mean flow. These restrictions strongly deviate from restrictions for the channel with flat bottom topography
Ratchet effects in two-dimensional systems with a lateral periodic potential
Radiation-induced ratchet electric currents have been studied theoretically
in graphene with a periodic noncentrosymmetric lateral potential. The ratchet
current generated under normal incidence is shown to consist of two
contributions, one of them being polarization-independent and proportional to
the energy relaxation time, and another controlled solely by elastic scattering
processes and sensitive to both the linear and circular polarization of
radiation. Two realistic mechanisms of electron scattering in graphene are
considered. For short-range defects, the ratchet current is helicity-dependent
but independent of the direction of linear polarization. For the Coulomb
impurity scattering, the ratchet current is forbidden for the radiation
linearly polarized in the plane perpendicular to the lateral-potential
modulation direction. For comparison, the ratchet currents in a quantum well
with a lateral superlattice are calculated at low temperatures with allowance
for the dependence of the momentum relaxation time on the electron energy.Comment: 8 pages, 4 figure
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