Accuracy of circular polarization as a measure of spin polarization in quantum dot qubits

A quantum dot spin LED provides a test of carrier spin injection into a qubit, as well as a means of analyzing carrier spin injection in general and local spin polarization. The polarization of the observed light is, however, significantly influenced by the dot geometry so the spin may be more polarized than the emitted light would naively suggest. We have calculated carrier polarization-dependent optical matrix elements using 8-band strain-dependent k.p theory for InAs/GaAs self-assembled quantum dots (SAQDs) for electron and hole spin injection into a range of quantum dot sizes and shapes, and for arbitrary emission directions. The observed circular polarization does not depend on whether the injected spin-polarized carriers are electrons or holes, but is strongly influenced by the SAQD geometry and emission direction. Calculations for typical SAQD geometries with emission along [110] show light that is only ~5% circularly polarized for spin states that are 100% polarized along [110]. Therefore observed polarizations [Chye et al. PRB 66, 201301(R)] of ~1% imply a spin polarization within the dot of ~20%. We also find that measuring along the growth direction gives near unity conversion of spin to photon polarization, and is the least sensitive to uncertainties in SAQD geometry.Comment: 4 pages, 6 figure

Comparison of lunar rocks and meteorites: Implications to histories of the moon and parent meteorite bodies

A number of similarities between lunar and meteoritic rocks are reported and suggest that the comparison is essential for a clear understanding of meteorites as probes of the early history of the solar systems: (1) Monomict and polymict breccias occur in lunar rocks, as well as in achondritic and chondritic meteorites, having resulted from complex and repeated impact processes. (2) Chondrules are present in lunar, as well as in a few achondritic and most chondritic meteorites. It is pointed out that because chondrules may form in several different ways and in different environments, a distinction between the different modes of origin and an estimate of their relative abundance is important if their significance as sources of information on the early history of the solar system is to be clearly understood. (3) Lithic fragments are very useful in attempts to understand the pre- and post-impact history of lunar and meteoritic breccias. They vary from little modified (relative to the apparent original texture), to partly or completely melted and recrystallized lithic fragments

Nuclear spin pumping and electron spin susceptibilities

In this work we present a new formalism to evaluate the nuclear spin dynamics driven by hyperfine interaction with non-equilibrium electron spins. To describe the dynamics up to second order in the hyperfine coupling, it suffices to evaluate the susceptibility and fluctuations of the electron spin. Our approach does not rely on a separation of electronic energy scales or the specific choice of electronic basis states, thereby overcoming practical problems which may arise in certain limits when using a more traditional formalism based on rate equations.Comment: 9 pages, 2 figure

Effect of hydrogen on deformation structure and properties of CMSX-2 nickel-base single-crystal superalloy

Material used in this study was a heat of the alloy CMSX-2. This nickel-based superalloy was provided in the form of oriented single crystals, solutionized for 3 hrs at 1315 C. It was then usually heat treated as follows: 1050 C/16h/air cool + 850 C/48h/air cool. The resulting microstructure is dominated by cuboidal, ordered gamma precipitates with a volume fraction of about 75% and an average size of 0.5 microns. In brief, the most compelling hydrogen induced-changes in deformation structure are: (1) enhanced dislocation accumulation in the gamma matrix; and (2) more extensive cross-slip of superdislocations in the gamma precipitates. The enhanced dislocation density in gamma acts to decrease the mean free path of a superdislocation, while easier cross slip hinders superdislocation movement by providing pinning points in the form of sessile jobs. Both processes contribute to the increase of flow stress and the notable work hardening that occurs prior to fracture

Interaction Effects in Conductivity of Si Inversion Layers at Intermediate Temperatures

We compare the temperature dependence of resistivity \rho(T) of Si MOSFETs with the recent theory by Zala et al. This comparison does not involve any fitting parameters: the effective mass m* and g*-factor for mobile electrons have been found independently. An anomalous increase of \rho with temperature, which has been considered a signature of the "metallic" state, can be described quantitatively by the interaction effects in the ballistic regime. The in-plane magnetoresistance \rho(B) is qualitatively consistent with the theory; however, the lack of quantitative agreement indicates that the magnetoresistance is more susceptible to the sample-specific effects than \rho(T).Comment: 4 pages, 5 figures. References update

Superlattice properties of carbon nanotubes in a transverse electric field

Electron motion in a (n,1) carbon nanotube is shown to correspond to a de Broglie wave propagating along a helical line on the nanotube wall. This helical motion leads to periodicity of the electron potential energy in the presence of an electric field normal to the nanotube axis. The period of this potential is proportional to the nanotube radius and is greater than the interatomic distance in the nanotube. As a result, the behavior of an electron in a (n,1) nanotube subject to a transverse electric field is similar to that in a semiconductor superlattice. In particular, Bragg scattering of electrons from the long-range periodic potential results in the opening of gaps in the energy spectrum of the nanotube. Modification of the bandstructure is shown to be significant for experimentally attainable electric fields, which raises the possibility of applying this effect to novel nanoelectronic devices.Comment: 7 pages, 3 figure

Lithic and mineral clasts in the Dar Al Gani (DAG) 319 polymict ureilite

Essentially all of the lithic and mineral clasts in DAG 319,a new polymict ureilite, were studied in order to determine their petrographic and mineralogical characteristics and their petrologic relationships to one another. Most of the clasts are identifiably from the ureilite parent body or appear to be shock-modified clasts from that body. Others appear to be projectiles derived from other bodies. The many kinds of lithic and mineral clasts found were classified into seven major groups, from A to G. The coarse-grained mafic lithic clasts (A) include three types of ureilitic lithology : type I ureilites, the predominant type, are similar to the common monomict ureilites; type II ureilites are a rare type with an olivine-orthopyroxene-augite lithology with essentially no carbon, and contain magmatic inclusions in the olivines and orthopyroxenes (similar to those in the Hughes 009 ureilite); a third type are magnesian ureilites with an mg >0.90,which are shock-produced. Fine-grained mafic lithic clasts (B) may have been derived from typical ureilites by shock, recrystallization, reduction, and/or melting. Felsic lithic clasts (C) are rare and important plagioclase-bearing igneous lithologies, which may represent the so-called missing basaltic melts separated during the formation of the ureilites. These represent several different lithic components. Dark clasts (D) consist mainly of phyllosilicates and sulfides, as well as magnetite (sometimes as framboidal clusters) and carbonates (dolomite, magnesite); some phyllosilicates occur as veins. Sulfide or metal-rich clasts (E) are shock-related, fine-grained lithologies to which sulfide and/or metal has been added; metal-rich clasts may have formed by reduction, and sulfide-rich clasts by oxidation. Rare chondrules and chondritic fragments (F) may be from projectiles which collided with the DAG 319 parent body, and they have characteristics that are more closely related to ordinary than to carbonaceous chondrites. Isolated mineral clasts (G) include many kinds of minerals produced by disaggregation of lithic clasts, but the origin of some of these minerals is uncertain. This paper describes all of these clasts, and is intended as a comprehensive study of the petrologic and mineralogical features of polymict ureilites. Such a description is a necessary prelude to a more complete understanding of the origin of the ureilitic meteorites