60,635 research outputs found
Spectroscopy of the parametric magnons excited by 4-wave process
Using a Magnetic Resonace Force Microscope, we have performed ferromagnetic
resonance (FMR) spectroscopy on parametric magnons created by 4-wave process.
This is achieved by measuring the differential response to a small source
modulation superimposed to a constant excitation power that drives the dynamics
in the saturation regime of the transverse component. By sweeping the applied
field, we observe abrupt readjustement of the total number of magnons each time
the excitation coincides with a parametric mode. This gives rise to
ultra-narrow peaks whose linewith is lower than of the applied
field.Comment: 4 page
Anharmonic parametric excitation in optical lattices
We study both experimentally and theoretically the losses induced by
parametric excitation in far-off-resonance optical lattices. The atoms confined
in a 1D sinusoidal lattice present an excitation spectrum and dynamics
substantially different from those expected for a harmonic potential. We
develop a model based on the actual atomic Hamiltonian in the lattice and we
introduce semiempirically a broadening of the width of lattice energy bands
which can physically arise from inhomogeneities and fluctuations of the
lattice, and also from atomic collisions. The position and strength of the
parametric resonances and the evolution of the number of trapped atoms are
satisfactorily described by our model.Comment: 7 pages, 5 figure
Non-linear spin-wave excitation at low bias fields
Non-linear magnetization dynamics is essential for the operation of many
spintronics devices. For microwave assisted switching of magnetic elements the
low field regime is of particular interest. In addition a large number of
experiments uses high amplitude FMR in order to generate d.c. currents via spin
pumping mechanism. Here we use time resolved X-ray magnetic circular dichroism
experiments to determine the number density of excited magnons in magnetically
soft Ni_80Fe_20 thin films at small bias fields and large rf-excitation
amplitudes. Our data shows that the common model of non-linear ferromagnetic
resonance is not suitable to describe the low bias field limit. Here we derive
a new model of parametric spin-wave excitation which correctly predicts
threshold amplitudes and decay rates also at low bias fields. In fact a new
series of critical modes with amplitude phase oscillations is found,
generalizing the theory of parametric spin-wave excitation
Response of discrete nonlinear systems with many degrees of freedom
We study the response of a large array of coupled nonlinear oscillators to
parametric excitation, motivated by the growing interest in the nonlinear
dynamics of microelectromechanical and nanoelectromechanical systems (MEMS and
NEMS). Using a multiscale analysis, we derive an amplitude equation that
captures the slow dynamics of the coupled oscillators just above the onset of
parametric oscillations. The amplitude equation that we derive here from first
principles exhibits a wavenumber dependent bifurcation similar in character to
the behavior known to exist in fluids undergoing the Faraday wave instability.
We confirm this behavior numerically and make suggestions for testing it
experimentally with MEMS and NEMS resonators.Comment: Version 2 is an expanded version of the article, containing detailed
steps of the derivation that were left out in version 1, but no additional
result
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