7 research outputs found
Semiclassical kinetic theory of electron spin relaxation in semiconductors
We develop a semiclassical kinetic theory for electron spin relaxation in
semiconductors. Our approach accounts for elastic as well as inelastic
scattering and treats Elliott-Yafet and motional-narrowing processes, such as
D'yakonov-Perel' and variable g-factor processes, on an equal footing. Focusing
on small spin polarizations and small momentum transfer scattering, we derive,
starting from the full quantum kinetic equations, a Fokker-Planck equation for
the electron spin polarization. We then construct, using a rigorous multiple
time scale approach, a Bloch equation for the macroscopic (-averaged)
spin polarization on the long time scale, where the spin polarization decays.
Spin-conserving energy relaxation and diffusion, which occur on a fast time
scale, after the initial spin polarization has been injected, are incorporated
and shown to give rise to a weight function which defines the energy averages
required for the calculation of the spin relaxation tensor in the Bloch
equation. Our approach provides an intuitive way to conceptualize the dynamics
of the spin polarization in terms of a ``test'' spin polarization which
scatters off ``field'' particles (electrons, impurities, phonons). To
illustrate our approach, we calculate for a quantum well the spin lifetime at
temperatures and densities where electron-electron and electron-impurity
scattering dominate. The spin lifetimes are non-monotonic functions of
temperature and density. Our results show that at electron densities and
temperatures, where the cross-over from the non-degenerate to the degenerate
regime occurs, spin lifetimes are particularly long.Comment: 29 pages, 10 figures, final versio
Polarized interacting exciton gas in quantum wells and bulk semiconductors
We develop a theory to calculate exciton binding energies of both two- and
three-dimensional spin polarized exciton gases within a mean field approach.
Our method allows the analysis of recent experiments showing the importance of
the polarization and intensity of the excitation light on the exciton
luminescence of GaAs quantum wells. We study the breaking of the spin
degeneracy observed at high exciton density . Energy
level splitting betwen spin +1 and spin -1 is shown to be due to many-body
inter-excitonic exchange while the spin relaxation time is controlled by
intra-exciton exchange.Comment: Revtex, 4 figures sent by fax upon request by e-mai
Propagation and Structure of Planar Streamer Fronts
Streamers often constitute the first stage of dielectric breakdown in strong
electric fields: a nonlinear ionization wave transforms a non-ionized medium
into a weakly ionized nonequilibrium plasma. New understanding of this old
phenomenon can be gained through modern concepts of (interfacial) pattern
formation. As a first step towards an effective interface description, we
determine the front width, solve the selection problem for planar fronts and
calculate their properties. Our results are in good agreement with many
features of recent three-dimensional numerical simulations.
In the present long paper, you find the physics of the model and the
interfacial approach further explained. As a first ingredient of this approach,
we here analyze planar fronts, their profile and velocity. We encounter a
selection problem, recall some knowledge about such problems and apply it to
planar streamer fronts. We make analytical predictions on the selected front
profile and velocity and confirm them numerically.
(abbreviated abstract)Comment: 23 pages, revtex, 14 ps file