790 research outputs found
Electron-Phonon Interaction in Embedded Semiconductor Nanostructures
The modification of acoustic phonons in semiconductor nanostructures embedded
in a host crystal is investigated including corrections due to strain within
continuum elasticity theory. Effective elastic constants are calculated
employing {\em ab initio} density functional theory. For a spherical InAs
quantum dot embedded in GaAs barrier material, the electron-phonon coupling is
calculated. Its strength is shown to be suppressed compared to the assumption
of bulk phonons
Transport and Boundary Scattering in Confined Geometries: Analytical Results
We utilize a geometric argument to determine the effects of boundary
scattering on the carrier mean-free path in samples of various cross sections.
Analytic expressions for samples with rectangular and circular cross sections
are obtained. We also outline a method for incorporating these results into
calculations of the thermal conductivity.Comment: 35 pages, Late
Scaling of Heteroepitaxial Island Sizes
Monte Carlo simulations of an atomistic solid-on-solid model are used to
study the effect of lattice misfit on the distribution of two-dimensional
islands sizes as a function of coverage in the submonolayer
aggregation regime of epitaxial growth. Misfit promotes the detachment of atoms
from the perimeter of large pseudomorphic islands and thus favors their
dissolution into smaller islands that relieve strain more efficiently. The
number density of islands composed of atoms exhibits scaling in the form
\mbox{)} where is the average island size. Unlike the
case of homoepitaxy, a rate equation theory based on this observation leads to
qualitatively different behavior than observed in the simulations.Comment: 10 pages, LaTeX 2.09, IC-DDV-94-00
Irrational constants in positronium decays
We establish irrational constants, that contribute to the positronium
lifetime at and order. In particular we show, that a
new type of constants appear, which are not related to Euler--Zagier sums or
multiple values.Comment: Presented at 9th Workshop on Elementary Particle Theory: Loops and
Legs in Quantum Field Theory, Sondershausen, 20-25 Apr 2008. 6 pages, 3
figure
Quantum theory of intersubband polarons
We present a microscopic quantum theory of intersubband polarons,
quasiparticles originated from the coupling between intersubband transitions
and longitudinal optical phonons. To this aim we develop a second quantized
theory taking into account both the Fr\"ohlich interaction between phonons and
intersubband transitions and the Coulomb interaction between the intersubband
transitions themselves. Our results show that the coupling between the phonons
and the intersubband transitions is extremely intense, thanks both to the
collective nature of the intersubband excitations and to the natural tight
confinement of optical phonons. Not only the coupling is strong enough to
spectroscopically resolve the resonant splitting between the modes (strong
coupling regime), but it can become comparable to the bare frequency of the
excitations (ultrastrong coupling regime). We thus predict the possibility to
exploit intersubband polarons both for applied optoelectronic research, where a
precise control of the phonon resonances is needed, and also to observe
fundamental quantum vacuum physics, typical of the ultrastrong coupling regime
Unstable Growth and Coarsening in Molecular-Beam Epitaxy
The coarsening dynamics of three-dimensional islands on a growing film is
discussed. It is assumed that the origin of the initial instability of a planar
surface is the Ehrlich-Schwoebel step-edge barrier for adatom diffusion. Two
mechanisms of coarsening are identified: (i) surface diffusion driven by an
uneven distribution of bonding energies, and (ii) mound coalescence driven by
random deposition. Semiquantitative estimates of the coarsening time are given
in each case. When the surface slope saturates, an asymptotic dynamical
exponent is obtained.Comment: 12 pages, 4 figure
- …