11,499 research outputs found
Theory of double resonance magnetometers based on atomic alignment
We present a theoretical study of the spectra produced by
optical-radio-frequency double resonance devices, in which resonant linearly
polarized light is used in the optical pumping and detection processes. We
extend previous work by presenting algebraic results which are valid for atomic
states with arbitrary angular momenta, arbitrary rf intensities, and arbitrary
geometries. The only restriction made is the assumption of low light intensity.
The results are discussed in view of their use in optical magnetometers
Efficient Data Averaging for Spin Noise Spectroscopy in Semiconductors
Spin noise spectroscopy (SNS) is the perfect tool to investigate electron
spin dynamics in semiconductors at thermal equilibrium. We simulate SNS
measurements and show that ultrafast digitizers with low bit depth enable
sensitive, high bandwidth SNS in the presence of strong optical background shot
noise. The simulations reveal that optimized input load at the digitizer is
crucial for efficient spin noise detection while the bit depth influences the
sensitivity rather weakly
Light diffraction by a strong standing electromagnetic wave
The nonlinear quantum interaction of a linearly polarized x-ray probe beam
with a focused intense standing laser wave is studied theoretically. Because of
the tight focusing of the standing laser pulse, diffraction effects arise for
the probe beam as opposed to the corresponding plane wave scenario. A
quantitative estimate for realistic experimental conditions of the ellipticity
and the rotation of the main polarization plane acquired by the x-ray probe
after the interaction shows that the implementation of such vacuum effects is
feasible with future X-ray Free Electron Laser light.Comment: 5 pages, 2 figures. Published versio
Suppression of superconductivity in nanowires by bulk superconductors
Transport measurements were made on a system consisting of a zinc nanowire
array sandwiched between two bulk superconducting electrodes (Sn or In). It was
found that the superconductivity of Zn nanowires of 40 nm diameter is
suppressed either completely or partially by the superconducting electrodes.
When the electrodes are driven into their normal state by a magnetic field, the
nanowires switch back to their superconducting state. This phenomenon is
significantly weakened when one of the two superconducting electrodes is
replaced by a normal metal. The phenomenon is not seen in wires with diameters
equal to and thicker than 70 nm.Comment: 4 pages, 5 figure
Noise spectroscopy and interlayer phase-coherence in bilayer quantum Hall systems
Bilayer quantum Hall systems develop strong interlayer phase-coherence when
the distance between layers is comparable to the typical distance between
electrons within a layer. The phase-coherent state has until now been
investigated primarily via transport measurements. We argue here that
interlayer current and charge-imbalance noise studies in these systems will be
able to address some of the key experimental questions. We show that the
characteristic frequency of current-noise is that of the zero wavevector
collective mode, which is sensitive to the degree of order in the system. Local
electric potential noise measured in a plane above the bilayer system on the
other hand is sensitive to finite-wavevector collective modes and hence to the
soft-magnetoroton picture of the order-disorder phase transition.Comment: 5 pages, 2 figure
Effect of hypokinesia on blood microcirculation
Blood microcirculation in the region of the scleral bulbar conjunctiva and the nail folds on the fingers and toes was studied in 18 practically healthy men during 182 day antiorthostatic hypokinesia and 30 day rehabilitation period. Marked changes in microcirculation in the sclera and feet and less evident changes on the hands was revealed. A complex of special prophylactic physical exercises had a distinctly favorable effect on circulation in the hands
Superconductivity in the Sn-Ba-Sr-Y-Cu-O system
Since Bednorz and Muller discovered high-T(sub c) superconductivity in the La-Ba-Cu-O compound, several families of superconducting oxides have been synthesized. Here, researchers report the results of search for superconductivity in the compounds based on tin, which has a lone electron pair like Bi, Tl, Pb. The following compounds were synthesized: Sn1Ba1Sr1Cu3Ox, Sn1Ba1Ca1Cu3Ox, Sn1Ba1Mg1Cu3Ox, Sn1Sr1Ca1Cu3Ox, Sn1Sr1Mg1Cu3Ox, Sn1Ca1Mg1Cu3Ox. The initial components were oxides and carbonates of the appropriate elements. Standard firing-grinding procedure was used. Final heating was carried out at 960 C during 12 hours. Then the samples were cooled inside the furnace. All the synthesis cycles were carried out in air atmosphere. Among the synthesized compounds only Sn1Ba1Sr1Cu3Ox showed remarkable conductivity. Other compounds were practically dielectrics. Presence of a possible superconductivity in Sn1Ba1Sr1Cu3Ox was defined by using the Meissner effect. At low temperature a deviation from paramagnetic behavior is observed. The hysteresis loops obtained at lower temperatures undoubtly testify to the presence of a superconductive phase in the sample. However, the part of the superconductive phase in the Sn1Ba1Sr1Cu3Ox ceramic turned out to be small, less than 2 percent, which agrees with the estimation from magnetic data. In order to increase the content of the superconductive phase two-valent cations Ba, Sr were partially substituted by univalent (K) and three-valent ones (Y)
The Stabilization of Superconductivity by Magnetic Field in Out-of-Equilibrium Nanowires
A systematic study has been carried out on the previously reported
"magnetic-field-induced superconductivity" of Zn nanowires. By varying
parameters such as magnetic field orientation and wire length, the results
provide evidence that the phenomenon is a nonequilibrium effect associated with
the boundary electrodes. They also suggest there are two length scales
involved, the superconducting coherence length and quasiparticle relaxation
length. As wire lengths approach either of these length scales, the effect
weakens. We demonstrate that it is appropriate to consider the effect to be a
stabilization of superconductivity, that has been suppressed by an applied
current.Comment: (Updated Version) 9 pages, 8 figure
Skin effect with arbitrary specularity in Maxwellian plasma
The problem of skin effect with arbitrary specularity in maxwellian plasma
with specular--diffuse boundary conditions is solved. A new analytical method
is developed that makes it possible to to obtain a solution up to an arbitrary
degree of accuracy. The method is based on the idea of symmetric continuation
not only the electric field, but also electron distribution function. The
solution is obtained in a form of von Neumann series.Comment: 7 pages, 2 figure
Photon splitting in a laser field
Photon splitting due to vacuum polarization in a laser field is considered.
Using an operator technique, we derive the amplitudes for arbitrary strength,
spectral content and polarization of the laser field. The case of a
monochromatic circularly polarized laser field is studied in detail and the
amplitudes are obtained as three-fold integrals. The asymptotic behavior of the
amplitudes for various limits of interest are investigated also in the case of
a linearly polarized laser field. Using the obtained results, the possibility
of experimental observation of the process is discussed.Comment: 31 pages, 4 figure
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