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We calculate the static longitudinal polarizability of single-wall carbon tubes in the long wavelength limit taking into account spin-orbit effects. We use a four-orbital orthogonal tight-binding formalism to describe the electronic states and the random phase approximation to calculate the dielectric function. We study the role of both the Rashba as well as the intrinsic spin-orbit interactions on the longitudinal dielectric response, i.e., when the probing electric field is parallel to the nanotube axis. The spin-orbit interaction modifies the nanotube electronic band dispersions, which may especially result in a small gap opening in otherwise metallic tubes. The bandgap size and state features, the result of competition between Rashba and intrinsic spin-orbit interactions, result in drastic changes in the longitudinal static polarizability of the system. We discuss results for different nanotube types and the dependence on nanotube radius and spin-orbit couplings. [ABSTRACT FROM AUTHOR]

This study presents a quantum-mechanical free electron model for analyzing a spin polarized transport and current-perpendicular-to-the-plane giant magnetoresistance (CPP-GMR) in a more realistic way. The CPP-GMR is evaluated by using three spin resolved conductance parameters based on the Landauer conductance formula. In a ballistic regime, a transfer-matrix method is used to calculate the spin dependent transmission probability as a function of the transverse mode. A spin dependent conduction band structure is constructed by extracting parameters of the free electron model, such as the atomic magnetic moments and the conduction electron densities, from the spin dependent layer-decomposed density of states of the Cu and Co interfacial layers in a Cu5/Co11 slab; these calculations are derived from the density functional theory. As a result, this study shows that the CPP-GMR in a [Cu(5 ML)/Co(11 ML)]n magnetic multilayer (n=2–5) with a 35 ML×35 ML cross section is in the range of 60%–111%. It is qualitatively comparable to the calculation results of first principles. This study also uses transmission probability to explain the increase of spin dependent scattering and CPP-GMR as a function of the number of layers in the [Cu/Co]n magnetic multilayer. Moreover, the study confirms that modification of the free electron model by quantum-mechanical methods can be applied to calculations of a spin polarized transport and CPP-GMR in a specific material system. [ABSTRACT FROM AUTHOR]

We present a detailed study of quasi-ballistic transport in submicron semiconductor channels. The electron distribution in such channels differs significantly from a near-equilibrium, shifted Maxwell-Boltzmann distribution function, and displays a large broadening, as well as pronounced features, peaks and shoulders, in the high-velocity tail of the distribution associated with the nonequilibrium and quasi-ballistic nature of the electron transport. For submicron channel lengths, analyses of the spatial dependence of the velocity distribution function show that scattering in the entire channel is important and that the scattering efficiency has a strong spatial dependence. In this article, we particularly study the crossover between the diffusive and quasi-ballistic regimes of transport and find characteristic signatures in (i) the electrostatics, which manifests as a redistribution of the voltage drop from the channel to the contact regions; (ii) the electron density, where exponential and linear spatial dependences of the source-injected and channel- and drain-backscattered electron densities are signatures of diffusive and quasi-ballistic transport, respectively, and (iii) the electron distribution function, where the source-injected ballistic peak observed in the quasi-ballistic regime disappears at the onset of diffusive transport. [ABSTRACT FROM AUTHOR]

Presents information on a study that calculated conductance in a multiply connected nanostructure with a quantum box geometry. Methodology of the study; Results and discussion on the study; Conclusions.

Proposes a novel electronic quantum interferometer which exhibits strong quantum interference effects in the ballistic regime. Production of strong conductance oscillations; Dependence of the effects on electron path length and temperature; Periodicity of the oscillations.

Resonant energy transfer is a mechanism for excitation exchange in quantum dot arrays. We explore this process by calculating the coupling strength, and by studying the detailed dynamics of extended coherent exciton states created in an array of quantum dots. Estimates of the Förster coupling VF are obtained from a microscopic description of the exciton levels in the quantum dot. We present results for different materials (CdS, CdSe, GaAs, and InP) as function of dot features. VF shows a nonmonotonic variation with a maximum value that depends on the specific dot sizes, material parameters, and dot separation. Analysis of coupled quantum dots using the time evolution of the density matrix when the Förster channel is open shows that a coherent coupling appears in different regimes. Realistic parameters, used throughout the study of the dynamics, suggest the practical realization of these phenomena in actual systems. [ABSTRACT FROM AUTHOR]

We report on a study of quasiballistic transport in deep submicron, inhomogeneous semiconductor structures, focusing on the analysis of signatures found in the full nonequilibrium electron distribution. We perform self-consistent numerical calculations of the Poisson-Boltzmann equations for a model n+-n--n+ GaAs structure and realistic, energy-dependent scattering. We show that, in general, the electron distribution displays significant, temperature dependent broadening and pronounced structure in the high-velocity tail of the distribution. The observed characteristics have a strong spatial dependence, related to the energy dependence of the scattering, and the large inhomogeneous electric field variations in these systems. We show that in this quasiballistic regime, the high-velocity tail structure is due to pure ballistic transport, whereas the strong broadening is due to electron scattering within the channel, and at the source(drain) interfaces. [ABSTRACT FROM AUTHOR]

Studies the Zeeman splitting of the donor spectra in cubic and hexagonal GaN using an effective mass theory approach. Description of the chemical shift of the different substitutional dopants using soft-core pseudopotentials; Donor ground states calculated.

Studies the simulation of hyperthermal deposition of Si and C on SiC surfaces. Sticking probabilities of adatoms; Efficient transfer of adatom energy to the substrate; Attractive forces experienced by the impinging adatom over the entire surface.