Microwave-induced resistance oscillations and zero-resistance states in 2D electron systems with two occupied subbands

We report on theoretical studies of recently discovered microwave-induced resistance oscillations and zero resistance states in Hall bars with two occupied subbands. In the same results, resistance presents a peculiar shape which appears to have a built-in interference effect not observed before. We apply the microwave-driven electron orbit model, which implies a radiation-driven oscillation of the two-dimensional electron system. Thus, we calculate different intra and inter-subband electron scattering rates and times that are revealing as different microwave-driven oscillations frequencies for the two electronic subbands. Through scattering, these subband-dependent oscillation motions interfere giving rise to a striking resistance profile. We also study the dependence of irradiated magnetoresistance with power and temperature. Calculated results are in good agreement with experiments.Comment: 7 pages, 6 figure

Upper-surface blowing nacelle design study for a swept wing airplane at cruise conditions

A study was made to design two types of overwing nacelles for an existing wing-body at a design condition of Mach = 0.8 and C sub L = 0.2. Internal and external surface contours were developed for nacelles having either a D-shaped nozzle or a high-aspect-ratio nozzle for upper-surface blowing in the powered-lift mode of operation. The goal of the design was the development of external nacelle lines that would minimize high-speed aerodynamic interference effects. Each nacelle type was designed for both two- and four-engine airplanes using an iterative process of aerodynamic potential flow analysis. Incremental nacelle drag estimates were made for flow-through wind tunnel models of each configuration

Pattern Competition in the Photorefractive Semiconductors

We analytically study the photorefractive Gunn effect in n-GaAs subjected to two external laser beams which form a moving interference pattern (MIP) in the semiconductor. When the intensity of the spatially independent part of the MIP, denoted by $I_0$, is small, the system has a periodic domain train (PDT), consistent with the results of linear stability analysis. When $I_0$ is large, the space-charge field induced by the MIP will compete with the PDT and result in complex dynamics, including driven chaos via quasiperiodic route

A rhoptry antigen of Plasmodium falciparum is protective in Saimiri monkeys

A non-polymorphic antigen associated with the rhoptry organelles of Plasmodium falciparum has been purified by immuno-affinity chromatography. The antigen, RAP-1 (rhoptry associated protein-1). which is defined by monoclonal antibodies which inhibit parasite growth in vitro, is a multi-component antigen consisting of four major proteins of 80, 65, 42 and 40 kDa and two minor proteins of 77 and 70 kDa. These proteins were electro-eluted from preparative sodium dodecyl sulphate polyacrylamide gels and protected Saimiri sciureus monkeys from a lethal blood-stage infection of P. falciparum malaria. Sera from the protected animals recognized only proteins of the RAP-1 antigen when used to probe a Western blot of total parasite protein extract, confirming that RAP-1 is responsible for eliciting the protective immune respons

Sub-linear radiation power dependence of photo-excited resistance oscillations in two-dimensional electron systems

We find that the amplitude of the $R_{xx}$ radiation-induced magnetoresistance oscillations in GaAs/AlGaAs system grows nonlinearly as $A \propto P^{\alpha}$ where $A$ is the amplitude and the exponent $\alpha < 1$. %, with $\alpha \rightarrow 1/2$ in %the low temperature limit. This striking result can be explained with the radiation-driven electron orbits model, which suggests that the amplitude of resistance oscillations depends linearly on the radiation electric field, and therefore on the square root of the power, $P$. We also study how this sub-linear power law varies with lattice temperature and radiation frequency.Comment: 5 pages, 3 figure

Cooling of cryogenic electron bilayers via the Coulomb interaction

Heat dissipation in current-carrying cryogenic nanostructures is problematic because the phonon density of states decreases strongly as energy decreases. We show that the Coulomb interaction can prove a valuable resource for carrier cooling via coupling to a nearby, cold electron reservoir. Specifically, we consider the geometry of an electron bilayer in a silicon-based heterostructure, and analyze the power transfer. We show that across a range of temperatures, separations, and sheet densities, the electron-electron interaction dominates the phonon heat-dissipation modes as the main cooling mechanism. Coulomb cooling is most effective at low densities, when phonon cooling is least effective in silicon, making it especially relevant for experiments attempting to perform coherent manipulations of single spins.Comment: 9 pages, 5 figure

Energy bands, conductance and thermoelectric power for ballistic electrons in a nanowire with spin-orbit interaction

We calculated the effects of spin-orbit interaction (SOI) on the energy bands, ballistic conductance and the electron-diffusion thermoelectric power of a nanowire by varying the temperature, electron density and width of the wire. The potential barriers at the edges of the wire are assumed to be very high. A consequence of the boundary conditions used in this model is determined by the energy band structure, resulting in wider plateaus when the electron density is increased due to larger energy-level separation as the higher subbands are occupied by electrons. The nonlinear dependence of the transverse confinement on position with respect to the well center excludes the "pole-like feature" in the conductance which is obtained when a harmonic potential is employed for confinement. At low temperature, the electron diffusion thermoelectric power increases linearly with T but deviates from the linear behavior for large values of T.Comment: Updated corrected version of the original submissio

Electron-phonon scattering in quantum point contacts

We study the negative correction to the quantized value $2e^2/h$ of the conductance of a quantum point contact due to the backscattering of electrons by acoustic phonons. The correction shows activated temperature dependence and also gives rise to a zero-bias anomaly in conductance. Our results are in qualitative agreement with recent experiments studying the 0.7 feature in the conductance of quantum point contacts.Comment: 4 pages, no figure

Protecting Long-term Commitment: Legal and Organizational Means

International audienc

Quantum well infrared photodetectors hardiness to the non ideality of the energy band profile

We report results on the effect of a non-sharp and disordered potential in Quantum Well Infrared Photodetectors (QWIP). Scanning electronic transmission microscopy is used to measure the alloy profile of the structure which is shown to present a gradient of composition along the growth axis. Those measurements are used as inputs to quantify the effect on the detector performance (peak wavelength, spectral broadening and dark current). The influence of the random positioning of the doping is also studied. Finally we demonstrate that QWIP properties are quite robust with regard to the non ideality of the energy band profile