4 research outputs found
Dynamics of Vortex Nucleation in Nanomagnets with Broken Symmetry
We investigate fundamental processes that govern dynamics of vortex
nucleation in sub-100 nm mesoscopic magnets. We focus on a structure with
broken symmetry - Pacman-like nanomagnet shape - in which we study
micromagnetic behavior both by means of a simple model and numerically. We show
that it is possible to establish desired vortex chirality and polarity by
applying only quasi-static in-plane magnetic field along specific directions.
We identify the modes of vortex nucleation that are very robust against
external magnetic field noise. These vortex nucleation modes are common among
wide range of sub-100 nm magnets with broken rotational symmetry.Comment: 5 pages, 4 figure
Frictional drag between quantum wells mediated by phonon exchange
We use the Kubo formalism to evaluate the contribution of acoustic phonon
exchange to the frictional drag between nearby two-dimensional electron
systems. In the case of free phonons, we find a divergent drag rate
(). However, becomes finite when phonon
scattering from either lattice imperfections or electronic excitations is
accounted for. In the case of GaAs quantum wells, we find that for a phonon
mean free path smaller than a critical value, imperfection
scattering dominates and the drag rate varies as over many
orders of magnitude of the layer separation . When exceeds the
critical value, the drag rate is dominated by coupling through an
electron-phonon collective mode localized in the vicinity of the electron
layers. We argue that the coupled electron-phonon mode may be observable for
realistic parameters. Our theory is in good agreement with experimental results
for the temperature, density, and -dependence of the drag rate.Comment: 45 pages, LaTeX, 8 postscript file figure