133,381 research outputs found
Localization of transverse waves in randomly layered media at oblique incidence
We investigate the oblique incidence of transverse waves on a randomly
layered medium in the limit of strong disorder. An approximate method for
calculating the inverse localization length based on the assumptions of zero
energy flux and complete phase stochastization is presented. Two effects not
found at normal incidence have been studied: dependence of the localization
length on the polarization, and decrease of the localization length due to the
internal reflections from layers with small refractive indexes. The inverse
localization length (attenuation rate) for P-polarized radiation is shown to be
always smaller than that of S-waves, which is to say that long enough randomly
layered sample polarizes transmitted radiation. The localization length for
P-polarization depends non-monotonically on the angle of propagation, and under
certain conditions turns to infinity at some angle, which means that typical
(non-resonant) random realizations become transparent at this angle of
incidence (stochastic Brewster effect).Comment: 12 pages, 1 figure, accepted for publication in Physical Review
Magnetoresistance of atomic-scale electromigrated nickel nanocontacts
We report measurements of the electron transport through atomic-scale
constrictions and tunnel junctions between ferromagnetic electrodes. Structures
are fabricated using a combination of e-beam lithography and controlled
electromigration. Sample geometries are chosen to allow independent control of
electrode bulk magnetizations. As junction size is decreased to the single
channel limit, conventional anisotropic magnetoresistance (AMR) increases in
magnitude, approaching the size expected for tunneling magnetoresistance (TMR)
upon tunnel junction formation. Significant mesoscopic variations are seen in
the magnitude and sign of the magnetoresistance, and no evidence is found of
large ballistic magnetoresistance effects.Comment: 3 pages, 3 figure
Dynamics of coupled vortices in layered magnetic nanodots
The spin dynamics are calculated for a model system consisting of
magnetically soft, layered nanomagnets, in which two ferromagnetic (F)
cylindrical dots, each with a magnetic vortex ground state, are separated by a
non-magnetic spacer (N). This permits a study of the effects of interlayer
magnetostatic interactions on the vortex dynamics. The system was explored by
applying the equations of motion for the vortex core positions. The restoring
force was calculated taking into account the magnetostatic interactions
assuming a realistic surface charge free spin distribution. For tri-layer F/N/F
dots with opposite chiralities and the same core polarizations (lowest energy
state), two eigenmodes are predicted analytically and confirmed via
micromagnetic simulations. One mode is in the sub-GHz range for submicron dot
diameters and corresponds to quasi-circular rotation of the cores about the dot
center. A second mode is in the MHz range corresponding to a small amplitude
rotation of the mean core position. The eigenfrequencies depend strongly on the
geometrical parameters of the system, suggesting that magnetostatic effects
play a dominant role in determining the vortex dynamics.Comment: One PDF file including text and 4 figure
Coherent description of electrical and thermal impurity-and-phonon limited transport in simple metals
The electrical resistivity, thermoelectric power and electronic thermal
conductivity of simple (isotropic) metals are studied in a uniform way.
Starting from results of a variational solution of the Boltzmann equation, a
generalized Matthiessen rule is used in order to superpose the inelastic (or
not) electron-phonon and elastic electron-impurity scattering cross sections
("matrix elements"). The temperature dependence relative to these processes is
given through simple functions and physical parameters over the usually
investigated range of temperature for each transport coefficient. The coherence
of such results is emphasized.Comment: 22 pages, 5 figures; to appear in International Journal of Modern
Physics
Dispersion and transitions of dipolar plasmon modes in graded plasmonic waveguides
Coupled plasmon modes are studied in graded plasmonic waveguides, which are
periodic chains of metallic nanoparticles embedded in a host with gradually
varying refractive indices. We identify three types of localized modes called
"light", "heavy", and "light-heavy" plasmonic gradons outside the passband,
according to various degrees of localization. We also demonstrate new
transitions among extended and localized modes when the interparticle
separation is smaller than a critical , whereas the three types of
localized modes occur for , with no extended modes. The transitions can
be explained with phase diagrams constructed for the lossless metallic systems.Comment: Preliminary results have been presented at ETOPIM 7. Submitted to
Appl. Phys. Let
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