Spectral Asymptotics for Higher-Order Ordinary Differential Equations

This paper gives one-term componentwise asymptotics for theM and spectral matrices of a self-adjoint realisation of aneven-order ordinary differential expression. The underlyinginterval is assumed to have at least one regular endpoint, andthe boundary conditions are supposed to be separated. Furthermore,the weight function and the reciprocal of the highest-ordercoefficient are supposed to be of regular variation at the regularendpoint, in the sense of Bingham, Goldie and Teugels. 1991Mathematics Subject Classification: 34B24, 34E05.     

Aharonov-Bohm oscillations in the presence of strong spin-orbit interactions

We have measured highly visible Aharonov-Bohm (AB) oscillations in a ring structure defined by local anodic oxidation on a p-type GaAs heterostructure with strong spin-orbit interactions. Clear beating patterns observed in the raw data can be interpreted in terms of a spin geometric phase. Besides h/e oscillations, we resolve the contributions from the second harmonic of AB oscillations and also find a beating in these h/2e oscillations. A resistance minimum at B=0 T, present in all gate configurations, is the signature of destructive interference of the spins propagating along time-reversed paths.     

Correlation of Electronic and Magnetic Properties of Thin Polymer Layers with Cobalt Nanoparticles

Nanoparticles (NPs) of cobalt are synthesized in shallow layers of polyimide using 40 keV implantation of Co⁺ ions with a few different fluences at various ion current densities. Nucleation of individual NPs at low fluencies and their percolation at high fluencies are crucial processes governing the electrical and magnetic properties of the metal/polymer nanocomposites that can be controlled by the implantation regimes. In particular, one can tune the magnetoresistance between negative and positive through appropriate choice of ion fluence and current density. The found non‐monotonous dependence of the magnetoresistance on the applied magnetic field allows suggestion of spin‐dependent domain wall scattering affecting the electron transport. The samples implanted with low fluencies demonstrate superparamagnetic behavior down to very low blocking temperatures. For high fluence (1.25 × 10¹⁷ cm⁻²) the transition to ferromagnetic ordering is observed that is related to the increased magnetic interaction of NPs.     

Growth optimization and characterization of lattice-matched Al0.82In0.18N optical confinement layer for edge emitting nitride laser diodes

We present the growth optimization and the doping by the metal organic chemical vapor deposition of lattice-matched Al_0.82In_0.18N bottom optical confinement layers for edge emitting laser diodes. Due to the increasing size and density of V-shaped defects in Al_1?xIn_xN with increasing thickness, we have designed an Al_1?xIn_xN/GaN multilayer structure by optimizing the growth and thickness of the GaN interlayer. The Al_1?xIn_xN and GaN interlayers in the multilayer structure were both doped using the same SiH₄ flow, while the Si levels in both layers were found to be significantly different by SIMS. The optimized 8×(Al_0.82In_0.18N/GaN=54/6 nm) multilayer structures grown on free-standing GaN substrates were characterized by high resolution X-ray diffraction, atomic force microscopy and transmission electron microscopy, along with the in-situ measurements of stress evolution during growth. Finally, lasing was obtained from the UV (394 nm) to blue (436 nm) wavelengths, in electrically injected, edge-emitting, cleaved-facet laser diodes with 480 nm thick Si-doped Al_1?xIn_xN/GaN multilayers as bottom waveguide claddings.     

Directed electron transport through a ballistic quantum dot under microwave radiation

Rectification of microwave radiation by asymmetric ballistic dot is studied at different frequencies (1-40 GHz), temperatures, and magnetic fields. Dramatic reduction of the rectification is found in magnetic fields at which the cyclotron radius of electron orbits at the Fermi level is less than the size of the dot. With respect to the magnetic field, both symmetric and antisymmetric contributions to the rectification are presented. The symmetric part changes significantly with microwave frequency omega at omegatau_{f}>/=1, where tau_{f} is the time of the ballistic electron flight across the dot. The results lead consistently towards the ballistic origin of the effect, and can be explained by strongly nonlocal electron response to the microwave electric field, which affects both speed and direction of the electron motion inside the dot.     

Resistance of a single domain wall in (Co/Pt)7 multilayer nanowires

Single (Co/Pt)_{7} multilayer nanowires prepared by electron beam lithography with perpendicular magnetic anisotropy are locally modified by means of Ga-ion implantation generating 180 degrees domain walls which are pinned at the edges of underlying thin Pt wires. Since we can exclude contributions from the anisotropic and the Lorentz magnetoresistance this allows us to determine the resistance of a single domain wall at room temperature. We find a positive relative resistance increase of DeltaR/R=1.8% inside the domain wall which agrees well with the model of Levy and Zhang [Phys. Rev. Lett. 79, 5110 (1997)10.1103/PhysRevLett.79.5110].     

Scaling of the low-temperature dephasing rate in Kondo systems

We present phase coherence time measurements in quasi-one-dimensional Ag wires doped with Fe Kondo impurities of different concentrations n_{s}. Because of the relatively high Kondo temperature T_{K} approximately 4.3 K of this system, we are able to explore a temperature range from above T_{K} down to below 0.01T_{K}. We show that the magnetic contribution to the dephasing rate gamma_{m} per impurity is described by a single, universal curve when plotted as a function of T/T_{K}. For T>0.1T_{K}, the dephasing rate is remarkably well described by recent numerical results for spin S=1/2 impurities. At lower temperature, we observe deviations from this theory. Based on a comparison with theoretical calculations for S>1/2, we discuss possible explanations for the observed deviations.     

TRPM5-expressing microvillous cells in the main olfactory epithelium

Background  

The main olfactory epithelium (MOE) in the nasal cavity detects a variety of air borne molecules that provide information regarding the presence of food, predators and other relevant social and environmental factors. Within the epithelium are ciliated sensory neurons, supporting cells, basal cells and microvillous cells, each of which is distinct in morphology and function. Arguably, the least understood, are the microvillous cells, a population of cells that are small in number and whose function is not known. We previously found that in a mouse strain in which the TRPM5 promoter drives expression of the green fluorescent protein (GFP), a population of ciliated olfactory sensory neurons (OSNs), as well as a population of cells displaying microvilli-like structures is labeled. Here we examined the morphology and immunocytochemical properties of these microvillous-like cells using immunocytochemical methods.     

Optical control of excitons in a pair of quantum dots coupled by the dipole-dipole interaction

We demonstrate coherent nonlinear-optical control of excitons in a pair of quantum dots (QDs) coupled via dipolar interaction. The single-exciton population in the first QD is controlled by resonant picosecond excitation, giving rise to Rabi oscillations. As a result, the exciton transition in the second QD is spectrally shifted and concomitant Rabi oscillations are observed. We identify coupling between permanent excitonic dipole moments as the dominant interaction mechanism, whereas quasiresonant (F?rster) energy transfer is weak. Such control schemes based on dipolar interaction are a prerequisite for realizing scalable quantum logic gates.