53 research outputs found
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
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 paÃses em desenvolvimento como o Brasil, os Ãndices 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 urbanÃsticoambiental 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 à s 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 UrbanÃstico. Direito à moradia. Cidade de São Paulo. Parque dos Búfalos
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
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
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
Evidence of Hot Carrier Extraction in Metal Halide Perovskite Solar Cells
The presence of hot carriers is presented in the operational properties of an
(FA,Cs)Pb(I, Br, Cl)3 solar cell at ambient temperatures and under practical
solar concentration. At 100 K, clear evidence of hot carriers is observed in
both the high energy tail of the photoluminescence spectra and from the
appearance of a non-equilibrium photocurrent at higher fluence in light J-V
measurements. At room temperature, however, the presence of hot carriers in the
emission at elevated laser fluence are shown to compete with a gradual red
shift in the PL peak energy as photo induced halide segregation begins to occur
at higher lattice temperature. The effects of thermionic emission of hot
carriers and the presence of a non-equilibrium carrier distribution are also
shown to be distinct from simple lattice heating. This results in large
unsaturated photocurrents at high powers as the Fermi distribution exceeds that
of the heterointerface controlling carrier transport and rectification
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