7,642 research outputs found
Connected component identification and cluster update on GPU
Cluster identification tasks occur in a multitude of contexts in physics and
engineering such as, for instance, cluster algorithms for simulating spin
models, percolation simulations, segmentation problems in image processing, or
network analysis. While it has been shown that graphics processing units (GPUs)
can result in speedups of two to three orders of magnitude as compared to
serial codes on CPUs for the case of local and thus naturally parallelized
problems such as single-spin flip update simulations of spin models, the
situation is considerably more complicated for the non-local problem of cluster
or connected component identification. I discuss the suitability of different
approaches of parallelization of cluster labeling and cluster update algorithms
for calculations on GPU and compare to the performance of serial
implementations.Comment: 15 pages, 14 figures, one table, submitted to PR
Suppression of spin-pumping by a MgO tunnel-barrier
Spin-pumping generates pure spin currents in normal metals at the ferromagnet
(F)/normal metal (N) interface. The efficiency of spin-pumping is given by the
spin mixing conductance, which depends on N and the F/N interface. We directly
study the spin-pumping through an MgO tunnel-barrier using the inverse spin
Hall effect, which couples spin and charge currents and provides a direct
electrical detection of spin currents in the normal metal. We find that
spin-pumping is suppressed by the tunnel-barrier, which is contrary to recent
studies that suggest that the spin mixing conductance can be enhanced by a
tunnel-barrier inserted at the interface
First principles calculation of polarization induced interfacial charges in GaN/AlN heterostructures
We propose a new method to calculate polarization induced interfacial charges
in semiconductor heterostructures using classical electrostatics applied to
real-space band diagrams from first principles calculations and apply it to
GaN/AlN heterostructures with ultrathin AlN layers (4-6 monolayers). We show
that the calculated electric fields and interfacial charges are independent of
the exchange-correlation functionals used (local-density approximation and
hybrid functionals). We also find the calculated interfacial charge of (6.8 +/-
0.4) x 10^13 cm-2 to be in excellent agreement with experiments and the value
of 6.58 x 10^13 cm-2 calculated from bulk polarization constants, validating
the use of bulk constants even for very thin films.Comment: 3 pages, 2 figures; submitted to Applied Physics Letter
Magnetic Vortex Core Dynamics in a Ferromagnetic Dot
We report direct imaging by means of x-ray photoemission electron microscopy
of the dynamics of magnetic vortices confined in micron-size circular Permalloy
dots that are 30 nm thick. The vortex core positions oscillate on a 10-ns
timescale in a self-induced magnetostatic potential well after the in-plane
magnetic field is turned off. The measured oscillation frequencies as a
function of the aspect ratio (thickness/radius) of the dots are in agreement
with theoretical calculations presented for the same geometry.Comment: 18 pages including 4 figure
Surface spin flip probability of mesoscopic Ag wires
Spin relaxation in mesoscopic Ag wires in the diffusive transport regime is
studied via nonlocal spin valve and Hanle effect measurements performed on
permalloy/Ag lateral spin valves. The ratio between momentum and spin
relaxation times is not constant at low temperatures. This can be explained
with the Elliott-Yafet spin relaxation mechanism by considering the momentum
surface relaxation time as being temperature dependent. We present a model to
separately determine spin flip probabilities for phonon, impurity and surface
scattering and find that the spin flip probability is highest for surface
scattering.Comment: 5 pages, 4 figure
Evidence of Vortex Jamming in Abrikosov Vortex Flux Flow Regime
We report on dynamics of non-local Abrikosov vortex flow in mesoscopic
superconducting Nb channels. Magnetic field dependence of the non-local voltage
induced by the flux flow shows that vortices form ordered vortex chains.
Voltage asymmetry (rectification) with respect to the direction of vortex flow
is evidence that vortex jamming strongly moderates vortex dynamics in
mesoscopic geometries. The findings can be applied to superconducting devices
exploiting vortex dynamics and vortex manipulation, including superconducting
wires with engineered pinning centers.Comment: 5 pages, 3 figure
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