1,295 research outputs found
Directing transport by polarized radiation in presence of chaos and dissipation
We study numerically the dynamics of particles on the Galton board of
semi-disk scatters in presence of monochromatic radiation and dissipation. It
is shown that under certain conditions the radiation leads to appearance of
directed transport linked to an underlining strange attractor. The direction of
transport can be efficiently changed by radiation polarization. The
experimental realization of this effect in asymmetric antidot superlattices is
discussed.Comment: revtex, 4 pages, 6 fig
Size effects in radiospectroscopy spectra of ferroelectric nanopowders
The theoretical and experimental investigation of ferroelectric nanopowders
is performed. The manifestation in radiospectroscopy spectra of size driven
ferroelectric-paraelectric phase transition at some critical particle average
size was the main goal of the consideration. In theoretical part the size
effect for the materials with ferroelectric tetragonal phase and cubic
paraelectric phase was considered allowing for the spontaneous polarization
inhomogeneity inside a particle and distribution of particle sizes. In ESR the
transformation of the spectra from tetragonal symmetry to cubic symmetry with
decreasing of nanoparticle sizes was calculated. Measurements of Fe3+ ESR
spectra in nanopowder of BaTiO3 were carried out at room temperature. The
decrease of intensity of tetragonal symmetry ESR lines of Fe3+ and appearance
of cubic symmetry line with asymmetry of the shoulders was observed with the
average sizes decrease with complete disappearance of tetragonal spectrum at
average size less or equal 40 nm. The comparison of the theory with experiment
was carried out. The value of critical size Rc = 40 nm was extracted from ESR
data. The asymmetry and broadening of right hand side shoulder of ESR cubic
symmetry line was shown to be related to contribution of paramagnetic centers
in the vicinity of the particles surface. The deconvolution of the cubic line
allowed to show, that this region size is about 3 nm.Comment: 10 pages, 8 figure
Photocurrent, Rectification, and Magnetic Field Symmetry of Induced Current Through Quantum Dots
We report mesoscopic dc current generation in an open chaotic quantum dot
with ac excitation applied to one of the shape-defining gates. For excitation
frequencies large compared to the inverse dwell time of electrons in the dot
(i.e., GHz), we find mesoscopic fluctuations of induced current that are fully
asymmetric in the applied perpendicular magnetic field, as predicted by recent
theory. Conductance, measured simultaneously, is found to be symmetric in
field. In the adiabatic (i.e., MHz) regime, in contrast, the induced current is
always symmetric in field, suggesting its origin is mesoscopic rectification.Comment: related papers at http://marcuslab.harvard.ed
Electron spin resonance investigation of Mn^{2+} ions and their dynamics in manganese doped SrTiO_3
Using electron spin resonance, lattice position and dynamic properties of
Mn2+ ions were studied in 0.5 and 2 % manganese doped SrTiO3 ceramics prepared
by conventional mixed oxide method. The measurements showed that Mn2+ ions
substitute preferably up to 97 % for Sr if the ceramics is prepared with a
deficit of Sr ions. Motional narrowing of the Mn2+ ESR spectrum was observed
when temperature increases from 120 K to 240-250 K that was explained as a
manifestation of off-center position of this ion at the Sr site. From the
analysis of the ESR spectra the activation energy Ea = 86 mV and frequency
factor 1/?0 ? (2-10)x10^(-14) 1/s for jumping of the impurity between
symmetrical off-center positions were determined. Both values are in agreement
with those derived previously from dielectric relaxation. This proves the
origin of dielectric anomalies in SrTiO3:Mn as those produced by the
reorientation dynamics of Mn2+ dipoles.Comment: 16 pages, 6 figure
Photocurrent in nanostructures with asymmetric antidots
The steady current induced by electromagnetic field in a 2D system with
asymmetric scatterers is studied. The scatterers are assumed to be oriented
cuts with one diffusive and another specular sides. Besides, the existence of
isotropic impurity scatterers is assumed. This simple model simulates the
lattice of half-disk which have been studied numerically recently. The model
allows the exact solution in the framework of the kinetic equation. The static
current response in the second order of electric field is obtained. The
photogalvanic tensor contains both responses to linear and circular
polarization of electromagnetic field. The model possesses non-analyticity with
regards to the rate of impurity scattering.Comment: 9 pages, 6 figure
Studies of h/e Aharonov-Bohm Photovoltaic Oscillations in Mesoscopic Au Rings
We have investigated a mesoscopic photovoltaic (PV) effect in micron-size Au
rings in which a dc voltage Vdc is generated in response to microwave
radiation. The effect is due to the lack of inversion symmetry in a disordered
system. Aharonov-Bohm PV oscillations with flux period h/e have been observed
at low microwave intensities for temperatures ranging from 1.4 to 13 K. For
moderate microwave intensities the h/e PV oscillations are completely quenched
providing evidence that the microwaves act to randomize the phase of the
electrons. Studies of the temperature dependence of Vdc also provide evidence
of the dephasing nature of the microwave field. A complete theoretical
explanation of the observed behavior seems to require a theory for the PV
effect in a ring geometry.Comment: 10 pages (RevTex twocolumn style), 8 figures-2 pages (one postscript
file) To be published in Phys. Rev.
- …