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