454 research outputs found
Phonon drag thermopower and weak localization
Previous experimental work on a two-dimensional (2D) electron gas in a
Si-on-sapphire device led to the conclusion that both conductivity and phonon
drag thermopower are affected to the same relative extent by weak
localization. The present paper presents further experimental and theoretical
results on these transport coefficients for two very low mobility 2D electron
gases in doped GaAs/GaAlAs quantum wells. The experiments
were carried out in the temperature range 3-7K where phonon drag dominates the
thermopower and, contrary to the previous work, the changes observed in the
thermopower due to weak localization were found to be an order of magnitude
less than those in the conductivity. A theoretical framework for phonon drag
thermopower in 2D and 3D semiconductors is presented which accounts for this
insensitivity of to weak localization. It also provides transparent
physical explanations of many previous experimental and theoretical results.Comment: 19 page Revtex file, 3 Postscript figur
A particle micro-macro decomposition based numerical scheme for collisional kinetic equations in the diffusion scaling
In this work, we derive particle schemes, based on micro-macro decomposition,
for linear kinetic equations in the diffusion limit. Due to the particle
approximation of the micro part, a splitting between the transport and the
collision part has to be performed, and the stiffness of both these two parts
prevent from uniform stability. To overcome this difficulty, the micro-macro
system is reformulated into a continuous PDE whose coefficients are no longer
stiff, and depend on the time step in a consistent way. This
non-stiff reformulation of the micro-macro system allows the use of standard
particle approximations for the transport part, and extends the work in [5]
where a particle approximation has been applied using a micro-macro
decomposition on kinetic equations in the fluid scaling. Beyond the so-called
asymptotic-preserving property which is satisfied by our schemes, they
significantly reduce the inherent noise of traditional particle methods, and
they have a computational cost which decreases as the system approaches the
diffusion limit
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