1,564 research outputs found
Synchronous versus asynchronous transport of a paramagnetic particle in a modulated ratchet potential
We present a combined experimental and theoretical study describing the
dynamical regimes displayed by a paramagnetic colloidal particle externally
driven above a stripe-patterned magnetic garnet film. A circularly polarized
rotating magnetic field modulates the stray field of the garnet film and
generates a translating periodic potential which induces particle motion.
Increasing the driving frequency, we observe a transition from a phase-locked
motion with constant speed to a sliding dynamics characterized by a lower speed
due to the loss of synchronization with the traveling potential. We explain the
experimental findings with an analytically tractable theoretical model and
interpret the particle dynamics in the presence of thermal noise. The model is
in good quantitative agreement with the experiments.Comment: 6 pages, 3 figures, published in Europhysics Letters (EPL
Clogging and Jamming of Colloidal Monolayers Driven Across a Disordered Landscape
We experimentally investigate the clogging and jamming of interacting
paramagnetic colloids driven through a quenched disordered landscape of fixed
obstacles. When the particles are forced to cross a single aperture between two
obstacles, we find an intermittent dynamics characterized by an exponential
distribution of burst size. At the collective level, we observe that quenched
disorder decreases the particle ow, but it also greatly enhances the "faster is
slower" effect, that occurs when increasing the particle speed. Further, we
show that clogging events may be controlled by tuning the pair interactions
between the particles during transport, such that the colloidal ow decreases
for repulsive interactions, but increases for anisotropic attraction. We
provide an experimental test-bed to investigate the crucial role of disorder on
clogging and jamming in driven microscale matter
Time-resolved spectra of a self-pulsing quantum dot laser
Self-sustained pulsations in the output of an InAs quantum dot laser diode in the MHz range are reported for the first time. The characteristics (shape, range and frequency) are presented for the free running laser and when optical feedback in the Littrow configuration is applied. The frequency resolved optical spectra reveal different envelope shifts between the two cases. This might be related to a change of phase-amplitude coupling across the gain maximum in agreement with the expectation for a two level system. The time scale and bifurcation scenario suggest that these are opto-thermal pulsation like those reported in quantum well amplifiers.(1
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