27,965 research outputs found
Magneto-Gyrotropic Photogalvanic Effects in Semiconductor Quantum Wells
Get PDFWe show that free-carrier (Drude) absorption of both polarized and unpolarized terahertz radiation in quantum well (QW) structures causes an electric photocurrent in the presence of an in-plane magnetic field. Experimental and theoretical analysis evidences that the observed photocurrents are spin-dependent and related to the gyrotropy of the QWs. Microscopic models for the photogalvanic effects in QWs based on asymmetry of photoexcitation and relaxation processes are proposed. In most of the investigated structures the observed magneto-induced photocurrents are caused by spin-dependent relaxation of non-equilibrium carriers
Influence of bottom topography on integral constraints in zonal flows with parameterized potential vorticity fluxes
Get PDFAn integral constraint for eddy fluxes of potential vorticity (PV), corresponding to global momentum conservation, is applied to two-layer zonal quasi-geostrophic channel flow. This constraint must be satisfied for any type of parameterization of eddy PV fluxes. Bottom topography strongly influence the integral constraint compared to a flat bottom channel. An analytical solution for the mean flow solution has been found by using asymptotic expansion in a small parameter which is the ratio of the Rossby radius to the meridional extent of the channel. Applying the integral constraint to this solution, one can find restrictions for eddy PV transfer coefficients which relate the eddy fluxes of PV to the mean flow. These restrictions strongly deviate from restrictions for the channel with flat bottom topography
Review: Spin photocurrents in quantum wells
No full textSpin photocurrents generated by homogeneous optical excitation with circularly polarized radiation in quantum wells (QWs) are reviewed. The absorption of circularly polarized light results in optical spin orientation due to the transfer of the angular momentum of photons to electrons of a two-dimensional electron gas. It is shown that in QWs belonging to one of the gyrotropic crystal classes a non-equilibrium spin polarization of uniformly distributed electrons causes a directed motion of electrons in the plane of the QW. A characteristic feature of this electric current, which occurs in unbiased samples, is that it reverses its direction upon changing the radiation helicity from left-handed to right-handed and vice versa. Two microscopic mechanisms are responsible for the occurrence of an electric current linked to a uniform spin polarization in a QW: the spin polarization-induced circular photogalvanic effect and the spin-galvanic effect. In both effects the current flow is driven by an asymmetric distribution of spin-polarized carriers in k-space of systems with lifted spin degeneracy due to k-linear terms in the Hamiltonian. Spin photocurrents provide methods to investigate spin relaxation and to reach a conclusion as regards the in-plane symmetry of QWs. The effect can also be utilized to develop fast detectors for determining the degree of circular polarization of a radiation beam. Furthermore, spin photocurrents under infrared excitation were used to demonstrate and investigate monopolar spin orientation of free carriers
Is the coefficient of eddy potential vorticity diffusion positive? Part1: barotropic zonal channel.
Get PDFThe question of whether the coefficient of diffusivity of potential vorticity by mesoscale eddies is positive is studied for a zonally reentrant barotropic channel using the quasi-geostrophic approach. The topography is limited to the first mode in the meridional direction but is unlimited in the zonal direction. We derive an analytic solution for the stationary (time-independent) solution. New terms associated with parameterized eddy fluxes of po-tential vorticity appear both in the equations for the mean zonal momentum balance, and the kinetic energy balance. These terms are linked with the topographic form stress exerted by parameterized eddies. It is demonstrated that in regimes with zonal flow (analogous to the Antarctic Circumpolar Current), the coefficient of eddy potential vorticity diffusivity must be positive
Modelling of N21P emission rates in aurora using various cross sections for excitation
No full textMeasurements of N21P auroral emissions from the (4,1) and (5,2)
bands have been made at high temporal and spatial resolution in
the region of the magnetic zenith. The instrument used was the
auroral imager ASK, situated at Ramfjordmoen, Norway (69.6 N,
19.2 E) on 22 October 2006. Measurements from the European
Incoherent Scatter Radar (EISCAT) have been combined with the
optical measurements, and incorporated into an ionospheric model
to obtain height profiles of electron density and emission rates
of the N21P bands. The radar data provide essential
verification that the energy flux used in the model is correct.
One of the most important inputs to the model is the cross section
for excitation to the B3Πg electronic state, as well as
the cross sections to higher states from which cascading into the
B state occurs. The balance equations for production and loss of
the populations of all levels in each state are solved in order to
find the cascade contributions. Several sets of cross sections
have been considered, and selected cross sections have been used
to construct "emission" cross sections for the observed bands. The
resulting brightnesses are compared with those measured by ASK.
The importance of specific contributions from cascading is found,
with more than 50% of the total brightness resulting from
cascading. The cross sections used are found to produce a range of
brightnesses well within the uncertainty of both the modelled and
measured values
Auroral ion acoustic wave enhancement observed with a radar interferometer system
Get PDFMeasurements of naturally enhanced ion acoustic line (NEIAL) echoes obtained with a five-antenna interferometric imaging radar system are presented. The observations were conducted with the European Incoherent SCATter (EISCAT) radar on Svalbard and the EISCAT Aperture Synthesis Imaging receivers (EASI) installed at the radar site. Four baselines of the interferometer are used in the analysis. Based on the coherence estimates derived from the measurements, we show that the enhanced backscattering region is of limited extent in the plane perpendicular to the geomagnetic field. Previously it has been argued that the enhanced backscatter region is limited in size; however, here the first unambiguous observations are presented. The size of the enhanced backscatter region is determined to be less than 900 × 500 m, and at times less than 160 m in the direction of the longest antenna separation, assuming the scattering region to have a Gaussian scattering cross section in the plane perpendicular to the geomagnetic field. Using aperture synthesis imaging methods volumetric images of the NEIAL echo are obtained showing the enhanced backscattering region to be aligned with the geomagnetic field. Although optical auroral emissions are observed outside the radar look direction, our observations are consistent with the NEIAL echo occurring on field lines with particle precipitation
Can sea surface height be used to estimate oceanic transport variability?
No full textThe relation between the sea surface height and the meridional transport across a zonal section at 26.5°N in the North Atlantic is studied by using an eddy resolving ocean state estimate simulated with the Massachusetts Institute of Technology general circulation model. It is shown that the correlation between the zonal sea surface height difference and transport can be substantially increased if the steric height contribution from the seasonal thermocline is removed. The latter explains a substantial part of sea surface height variability, but its effect on transport is weak. It is also found that the zonal steric height difference correlates well with the transport after the contribution of the seasonal thermocline has been removed. There is a similar agreement (with correlation coefficient of 0.63 for the full signal and 0.89 for the mean seasonal cycle) between the meridional transport and steric height based on observations from the Rapid Climate Change (RAPID) project
JETP Letters V. 65, I .10
No full textJETP Letters -- May 25, 1997
Volume 65, Issue 10, pp. 763-832
Possible origin and spectrum of ultrahigh-energy cosmic rays
A. V. Uryson
Full Text: PDF (72 kB)
Inclusive semileptonic decays of B mesons
S. Ya. Kotkovskii
Full Text: PDF (94 kB)
New possibilities for producing photon echoes from a homogeneous ensemble of atoms and with the use of a single light pulse
G. N. Nikolaev
Full Text: PDF (139 kB)
Quantum theory of cooling of atoms below the one-photon recoil energy by a pulsed field
A. V. Taichenachev, A. M. Tumaikin, and V. I. Yudin
Full Text: PDF (120 kB)
Properties of IR-active lattice vibrations in the vicinity of kinks in the Frenkel–Kontorova model
V. M. Burlakov and M. A. Moskalenko
Full Text: PDF (100 kB)
Quasiparticle dynamics and phase locking in a S–I–S multilayer Josephson junction
D. A. Ryndyk
Full Text: PDF (103 kB)
Solitary flexural waves on a supersonic domain wall in yttrium orthoferrite
M. V. Chetkin, Yu. N. Kurbatova, and V. N. Filatov
Full Text: PDF (689 kB)
Fine structure of excitonic levels in quantum dots
R. I. Dzhioev, B. P. Zakharchenya, E. L. Ivchenko, V. L. Korenev, Yu. G. Kusraev, N. N. Ledentsov, V. M. Ustinov, A. E. Zhukov, and A. F. Tsatsul'nikov
Full Text: PDF (118 kB)
Competition between nuclear ferromagnetism and superconductivity
A. M. Dyugaev, I. D. Vagner, and P. Wyder
Full Text: PDF (82 kB)
Localized states at the helicoidal phase transition
A. Buzdin and Y. Meurdesoif
Full Text: PDF (121 kB)
Stripe motion in CuO2 planes ofY1 – xPrxBa2Cu3O7 as observed from the Cu(2) quadrupole resonance
M. A. Teplov, Yu. A. Sakhratov, A. V. Dooglav, A. V. Egorov, E. V. Krjukov, and O. P. Zaitsev
Full Text: PDF (134 kB)
Observation of stochastic resonance in a monostable magnetic system
A. N. Grigorenko, P. I. Nikitin, and G. V. Roshchepkin
Full Text: PDF (97 kB)Archived web conten
Dynamics of finite-sized light spheres in turbulence
No full textWe report experimental results on the Lagrangian dynamics of finite-size light particles in turbulence. Using an orthogonal camera setup and 3D particle tracking, we study the velocity and acceleration statistics of rigid light spheres in a water tunnel with nearly homogeneous and isotropic turbulence. The Reynolds number (ReY) is varied from 180 to 300, and the study covers a range of size ratios (4 < D/η < 16) for marginally light spheres. We find that the normalised acceleration PDF decreases in intermittency with increasing size ratio - in qualitative agreement with the predictions of the Faxén corrected model. We also present preliminary results on the rotational dynamics of large light spheres in turbulence
Spin noise spectroscopy of a single quantum well microcavity
No full textWe report on an experimental observation of spin noise in a single semiconductor quantum well embedded into a microcavity. The great cavity-enhanced sensitivity to fluctuations of optical anisotropy has allowed us to measure the Kerr rotation and ellipticity noise spectra in the strong-coupling regime. The spin noise spectra clearly show two resonant features: a conventional magnetoresonant component shifting towards higher frequencies with a magnetic field and an unusual “nonmagnetic” component centered at zero frequency and getting suppressed with an increasing magnetic field. We attribute the first of them to the Larmor precession of free electron spins, whereas, the second one is presumably due to hyperfine electron-nuclei spin interactions
- …
