5,463 research outputs found
Spin Splitting Induced Photogalvanic Effect in Quantum Wells
A theory of the circular photogalvanic effect caused by spin splitting in
quantum wells is developed. Direct interband transitions between the hole and
electron size-quantized subbands are considered. The photocurrent excitation
spectrum is shown to depend strongly on the form of the spin-orbit interaction.
In the case of structure inversion asymmetry induced (Rashba) spin-splitting,
the current is a linear function of light frequency near the absorption edge,
and for the higher excitation energy the spectrum changes its sign and has a
minimum. In contrast, when the bulk inversion asymmetry (Dresselhaus splitting)
dominates, the photocurrent edge behavior is parabolic, and then the spectrum
is sign-constant and has a maximum.Comment: 5 pages, 5 figure
Production of UCN by Downscattering in superfluid He4
Ultra-cold neutrons (UCN) are neutrons with energies so low they can be
stored in material bottles and magnetic traps. They have been used to provide
the currently most accurate experiments on the neutron life time and electric
dipole moment. UCN can be produced in superfluid Helium at significantly higher
densities than by other methods. The predominant production process is usually
by one phonon emission which can only occur at a single incident neutron energy
because of momentum and energy conservation. However UCN can also be produced
by multiphonon processes. It is the purpose of this work to examine this
multiphonon production of UCN. We look at several different incident neutron
spectra, including cases where the multiphonon production is significant, and
see how the relative importance of multiphonon production is influenced by the
incident spectrum.Comment: 3 figures, improved presentation after comments from xxx reader
Shot noise in the interacting resonance level model
The shot noise power and the Fano factor of a spinless resonant level model
is calculated. The Coulomb interaction which in this model acts between the
lead electron and the impurity is considered in the first order approximation.
The logarithmic divergencies which appeared in the expressions for shot noise
and the transport current are removed by renormalization group analysis. It is
shown that Keldysh technique gives an adequate description of perturbation
theory results. By passing to the bosonized form of the resonance model it is
proven that in the strong interaction limit the tunnelling becomes irrelevant
and decreases.Comment: 4 pages, 2 figure
Limb Event Brightenings and Fast Ejection Using IRIS Mission Observations
The Interface Region Imaging Spectrograph (IRIS) of the NASA small explorer
mission provides significantly more complete and higher resolution spectral
coverage of the dynamical conditions inside the chromosphere and transition
region (TR) than has heretofore been available. Near the solar limb high
temporal, spatial (0.3") and spectral resolution observations from the
ultraviolet IRIS spectra reveal high-energy limb event brightenings (LEBs) at
low chromospheric heights, around 1 Mm above the limb. They can be
characterized as explosive events producing jets. We selected two events
showing spectra of a confined eruption just off or near the quiet Sun limb, the
jet part showing obvious moving material with short duration large Doppler
shifts in three directions identified as macrospicules on slit-jaw (SJ) images
in Si IV and He II 304 A. The events are analyzed from a sequence of very close
rasters taken near the central meridian and the South pole limb. The processed
SJ images and the simultaneously observed fast spectral sequences having large
Doppler shifts, with a pair of red shifted elements together with a faster blue
shifted element from almost the same position, are analyzed. Shifts correspond
to velocities of up to 100 km/s in projection on the plane of the sky. The
occurrence of erupting spicules and macrospicules from these regions is noticed
from images taken before and after the spectra. The cool low first ionization
potential (FIP) element simultaneous line emissions of the MgII h and k
resonance lines do not clearly show a similar signature due to optical
thickness effects but the Si IV broad-band SJ images do. The bidirectional
plasma jets ejected from a small reconnection site are interpreted as the
result of coronal loop-loop interactions leading to reconnection in nearby
sites.Comment: 24 pages, 16 figures., Accepted in Sol. Phy
- âŠ