Electrical Detection of Spin Accumulation at a Ferromagnet-Semiconductor Interface

We show that the accumulation of spin-polarized electrons at a forward-biased Schottky tunnel barrier between Fe and n-GaAs can be detected electrically. The spin accumulation leads to an additional voltage drop across the barrier that is suppressed by a small transverse magnetic field, which depolarizes the spins in the semiconductor. The dependence of the electrical accumulation signal on magnetic field, bias current, and temperature is in good agreement with the predictions of a drift-diffusion model for spin-polarized transport.Comment: Submitted to Phys. Rev. Let

Optical and electrical spin injection and spin transport in hybrid Fe/GaAs devices

We discuss methods for imaging the nonequilibrium spin polarization of electrons in Fe/GaAs spin transport devices. Both optically- and electrically-injected spin distributions are studied by scanning magneto-optical Kerr rotation microscopy. Related methods are used to demonstrate electrical spin detection of optically-injected spin polarized currents. Dynamical properties of spin transport are inferred from studies based on the Hanle effect, and the influence of strain on spin transport data in these devices is discussed.Comment: 5 pages, 6 figs. ICPS-28 proceedings (July'06, Vienna) for J. Appl. Phy

Interaction of an electron gas with photoexcited electron-hole pairs in modulation-doped GaAs and CdTe quantum wells

The nature of the correlated electron gas and its response to photo-injected electron-hole pairs in nominally undoped and modulation-doped multiple quantum-well (MQW) structures was studied by experiment and theory, revealing a new type of optically-active excitation, magnetoplasmons bound to a mobile valence hole. These excitations are blue-shifted from the corresponding transition of the isolated charged magnetoexciton X-. The observed blue-shift of X- is larger than that of two-electron negative donor D-, in agreement with theoretical predictions.Comment: 4 pages, 3 figures, EP2DS-14 manuscript, to be published in Physica

Spin relaxation of localized electrons in n-type semiconductors

The mechanisms that determine spin relaxation times of localized electrons in impurity bands of n-type semiconductors are considered theoretically and compared with available experimental data. The relaxation time of the non-equilibrium angular momentum is shown to be limited either by hyperfine interaction, or by spin-orbit interaction in course of exchange-induced spin diffusion. The energy relaxation time in the spin system is governed by phonon-assisted hops within pairs of donors with an optimal distance of about 4 Bohr radii. The spin correlation time of the donor-bound electron is determined either by exchange interaction with other localized electrons, or by spin-flip scattering of free conduction-band electrons. A possibility of optical cooling of the spin system of localized electrons is discussed.Comment: Submitted to the special issue "Optical Orientation", Semiconductor Science and Technolog

Conflito entre os direitos à moradia e ao meio ambiente : estudo de caso do 'Parque dos Búfalos' - Jardim Apurá/SP

Orientador : Manuel Munhoz CaleiroMonografia (especialização) - Universidade Federal do Paraná, Setor de Ciências Agrárias, Curso de Especialização em Direito AmbientalInclui referênciasResumo : Considerado o maior fenômeno do século XX, o processo de urbanização brasileiro, estimulado pela industrialização do eixo Sudeste-Sul e da consequente migração massiva de trabalhadores em busca de melhores condições de vida, continua em crescimento e traz a tona a discussão da ilegalidade urbana e dos diversos problemas socioambientais dela decorrente, em virtude do crescimento desordenado das cidades e da falta de planejamento urbano. É público e notório, nos países em desenvolvimento como o Brasil, os índices de pessoas que vivem na clandestinidade e sem acesso a uma propriedade digna para residência, em um local dotado de infraestrutura e de serviços essenciais. Neste contexto, o direito urbanísticoambiental em meio à gestão das cidades torna-se fundamental e requer uma maior eficácia quanto a sua interpretação, diante da dimensão da legislação e suas margens para conflitos entre direitos essenciais às pessoas. Essa é a situação que está sendo vivenciada na Zona Sul de São Paulo, no Parque dos Búfalos, bairro do Jardim Apurá, distrito de Cidade Ademar, local que estudaremos nesta pesquisa. Palavras-chave: Direito Ambiental. Direito Urbanístico. Direito à moradia. Cidade de São Paulo. Parque dos Búfalos

Spin dynamics in semiconductors

This article reviews the current status of spin dynamics in semiconductors which has achieved a lot of progress in the past years due to the fast growing field of semiconductor spintronics. The primary focus is the theoretical and experimental developments of spin relaxation and dephasing in both spin precession in time domain and spin diffusion and transport in spacial domain. A fully microscopic many-body investigation on spin dynamics based on the kinetic spin Bloch equation approach is reviewed comprehensively.Comment: a review article with 193 pages and 1103 references. To be published in Physics Reports

Anomalous circular polarization of magneto-photoluminescence from individual CdSe nanocrystals

We study the low-temperature magneto-photoluminescence (PL) from individual CdSe nanocrystals. Nanocrystals having a small "bright" exciton fine structure splitting ($<$0.5 meV) exhibit a conventional left- and right-circularly polarized Zeeman PL doublet in applied magnetic fields. In contrast, nanocrystals with large fine structure splitting ($>$1 meV) show an anomalous magneto-PL polarization, wherein the lower-energy peak becomes circularly polarized with increasing field, while the higher-energy peak remains linearly polarized. This unusual behavior arises from strong mixing between the absorbing and emitting bright exciton levels due to strong anisotropic exchange interactions.Comment: 15 pages, 3 figures; submitte