190 research outputs found
Time evolution of spin state of radical ion pair in microwave field: An analytical solution
The paper reports an exact solution for the problem of spin evolution of
radical ion pair in static magnetic and resonant microwave field taking into
account Zeeman and hyperfine interactions and spin relaxation. The values of
parameters that provide one of the four possible types of solution are
analysed. It is demonstrated that in the absence of spin relaxation, besides
the zero field invariant an invariant at large amplitudes of the resonant
microwave field can be found. The two invariants open the possibility for
simple calculation of microwave pulses to control quantum state of the radical
pair. The effect of relaxation on the invariants is analysed and it is shown
that changes in the high field invariant are induced by phase relaxation.Comment: 18 pages, 7 figure
Investigation of femtosecond photon echo in dye-doped polymer film at room temperature
Signals of primary and stimulated femtosecond photon echo were found and investigated at room temperature in a polyvinyl butyral film doped with phthalocyanine molecules. The decay curve of relative intensity and the spectrum of the signal of primary femtosecond photon echo were recorded. The physical mechanism of formation of such signals in a system of impurity centers excited through the phonon wing of the optical absorption band was discussed. © 2007 by Allerton Press, Inc
Stochastic Dynamics of Magnetosomes in Cytoskeleton
Rotations of microscopic magnetic particles, magnetosomes, embedded into the
cytoskeleton and subjected to the influence of an ac magnetic field and thermal
noise are considered. Magnetosome dynamics is shown to comply with the
conditions of the stochastic resonance under not-too-tight constraints on the
character of the particle's fastening. The excursion of regular rotations
attains the value of order of radian that facilitates explaining the biological
effects of low-frequency weak magnetic fields and geomagnetic fluctuations.
Such 1-rad rotations are effectively controlled by slow magnetic field
variations of the order of 200 nT.Comment: LaTeX2e, 7 pages with 3 figure
Hyperfine interaction and magnetoresistance in organic semiconductors
We explore the possibility that hyperfine interaction causes the recently
discovered organic magnetoresistance (OMAR) effect. Our study employs both
experiment and theoretical modelling. An excitonic pair mechanism model based
on hyperfine interaction, previously suggested by others to explain magnetic
field effects in organics, is examined. Whereas this model can explain a few
key aspects of the experimental data, we, however, uncover several fundamental
contradictions as well. By varying the injection efficiency for minority
carriers in the devices, we show experimentally that OMAR is only weakly
dependent on the ratio between excitons formed and carriers injected, likely
excluding any excitonic effect as the origin of OMAR.Comment: 10 pages, 7 figures, 1 tabl
Femtosecond photon echo in a dye-doped polymer film and the possibility of coherent optical cooling
The signals of primary and stimulated femtosecond photon echoes are investigated in a dye-doped polymer film at room temperature. The homogeneous S 0 → S 1 spectral line width, which is due to the interaction between the impurity molecules and the quasi-local low-frequency modes, is estimated (≈5 × 10 12 Hz). Special attention is paid to the study of spectra of femtosecond echo signals. The short-wave shifts of these spectra, with respect to the spectrum of femtosecond exciting pulses, are observed. These shifts indicate that the anti-Stokes regime of femtosecond pulse emission is realized. Therefore, the coherent regime of laser cooling of solids appears to be possible. The prospects of using of this new cooling regime in the function of a solid-state optical refrigerator are discussed. © Nauka/Interperiodica 2007
Peculiarities of femtosecond photon echo signals in dye-doped polymer films at high temperatures
Some results of femtosecond echo experiments on polyvinylbutyral polymer films doped with phtalocyanine molecules at high (up to room) temperatures are reported. Special attention is paid to the stimulated femtosecond photon echo (SFPE), which was observed in a solid-state medium at room temperature for the first time. A decay curve of the SFPE signal has been obtained and theoretically analyzed. The results of the analysis indicate that the random interaction between impurity molecules and quasi-localized low-frequency vibration modes in an amorphous matrix plays the dominant role in the character of optical dephasing at high temperatures. © Allerton Press, Inc 2008
EPR imaging study of paramagnetic centre distribution in thiokol-epoxy hermetics
The distribution of paramagnetic centres in carbon black filler in the interphase layer of the thiokol-epoxy hermetics on the border of brass or glass substrate was studied using EPR-imaging method. It was shown that the relative content of radicals decreases near the hermetic-"rigid" surface contact border. The thickness of the layer with a low concentration of radicals is estimated as 0.5±0.3 mm. The inhomogeneous distribution of radicals is more obvious in the case of hermetic hardening on a brass surface. These results are explained by a catalytic acceleration of the thiokol-epoxy polymerization reaction in the region of hermetic-metal surface contact. © 1996 Springer
Single Electron Spin Decoherence by Nuclear Spin Bath: Linked Cluster Expansion Approach
We develop a theoretical model for transverse dynamics of a single electron
spin interacting with a nuclear spin bath. The approach allows a simple
diagrammatic representation and analytical expressions of different nuclear
spin excitation processes contributing to electron spin decoherence and
dynamical phase fluctuations. It accounts for nuclear spin dynamics beyond
conventional pair correlation models. As an illustration of the theory, we
evaluated the coherence dynamics of a P donor electron spin in a Si crystal.Comment: 37 pages, 13 figure
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