1,509 research outputs found
Diffusion of Monochromatic Classical Waves
We study the diffusion of monochromatic classical waves in a disordered
acoustic medium by scattering theory. In order to avoid artifacts associated
with mathematical point scatterers, we model the randomness by small but finite
insertions. We derive expressions for the configuration-averaged energy flux,
energy density, and intensity for one, two and three dimensional (1D, 2D and
3D) systems with an embedded monochromatic source using the ladder
approximation to the Bethe-Salpeter equation. We study the transition from
ballistic to diffusive wave propagation and obtain results for the
frequency-dependence of the medium properties such as mean free path and
diffusion coefficient as a function of the scattering parameters. We discover
characteristic differences of the diffusion in 2D as compared to the
conventional 3D case, such as an explicit dependence of the energy flux on the
mean free path and quite different expressions for the effective transport
velocity.Comment: 11 pages, 2 figure
Charge Density Wave Ratchet
We propose to operate a locally-gated charge density wave as an electron
pump. Applying an oscillating gate potential with frequency causes equally
spaced plateaux in the sliding charge density wave current separated by where is the number of parallel chains. The effects of thermal
noise are investigated.Comment: To be published in Applied Physics Letter
Feedback control of noise in spin valves by the spin-transfer torque
The miniaturisation of magnetic read heads and random access memory elements
makes them vulnerable to thermal fluctuations. We demonstrate how
current-induced spin-transfer torques can be used to suppress the effects of
thermal fluctuations. This enhances the fidelity of perpendicular magnetic spin
valves. The simplest realization is a dc current to stabilize the free magnetic
layers. The power can be significantly reduced without losing fidelity by
simple control schemes, in which the stabilizing current-induced spin-transfer
torque is controlled by the instantaneous resistance.Comment: 4pages, 2 figure
Spin-transfer in diffusive ferromagnet-normal metal systems with spin-flip scattering
The spin-transfer in biased disordered ferromagnet (F) - normal metal (N)
systems is calculated by the diffusion equation. For F1-N2-F2 and
N1-F1-N2-F2-N3 spin valves, the effect of spin-flip processes in the normal
metal and ferromagnet parts are obtained analytically. Spin-flip in the center
metal N2 reduces the spin-transfer, whereas spin-flip in the outer normal
metals N1 and N3 can increase it by effectively enhancing the spin polarization
of the device.Comment: 9 pages, 3 figure
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