32,741 research outputs found
Spin-polarized current and shot noise in the presence of spin flip in a quantum dot via nonequilibrium Green's functions
Using non-equilibrium Green functions we calculate the spin-polarized current
and shot noise in a ferromagnet--quantum-dot--ferromagnet (FM-QD-FM) system.
Both parallel (P) and antiparallel (AP) magnetic configurations are considered.
Coulomb interaction and coherent spin-flip (similar to a transverse magnetic
field) are taken into account within the dot. We find that the interplay
between Coulomb interaction and spin accumulation in the dot can result in a
bias-dependent current polarization . In particular, can be
suppressed in the P alignment and enhanced in the AP case depending on the bias
voltage. The coherent spin-flip can also result in a switch of the current
polarization from the emitter to the collector lead. Interestingly, for a
particular set of parameters it is possible to have a polarized current in the
collector and an unpolarized current in the emitter lead. We also found a
suppression of the Fano factor to values well below 0.5.Comment: Published version. 13 pages, 7 figure
Os seis elementos: educação ambiental integrada para multiplicadores.
A Educação Ambiental é uma disciplina que busca educar gerando no ser humano a formação de uma consciência crítica e uma mudança de comportamento positiva em relação ao meio ambiente. Ela é fundamental para embutir nas mentes humanas a necessidade e a urgência de conservar e preservar o meio ambiente. O Programa de Educação Ambiental da Embrapa Florestas - PREA, criou o método Educação Ambiental Integrada - os Seis Elementos, o qual ressalta a interdependência entre os seis elementos naturais (ar, água, solo, flora e fauna incluindo o ser humano), fundamentais para a manutenção da vida no planeta. Ao ser humano, o sexto elemento, embora faça parte da fauna, é dado um destaque especial, por ser o único capaz de reverter o processo da degradação atual, recuperando e conservando o planeta. Para isso, durante a apresentação dos conteúdos são inseridas atividades de sensibilização com o objetivo de trabalhar o lado positivo do ser humano, mostrando que ele também é parte da natureza, valorizando-o como pessoa, construtor e agente de mudanças.bitstream/item/50880/1/Rachwal-Souza.pdfOrganizado por Patricia Póvoa de Mattos, Luciane Cristine Jaques e Katia Regina Pichelli
Orbital magnetism in axially deformed sodium clusters: From scissors mode to dia-para magnetic anisotropy
Low-energy orbital magnetic dipole excitations, known as scissors mode (SM),
are studied in alkali metal clusters. Subsequent dynamic and static effects are
explored. The treatment is based on a self-consistent microscopic approach
using the jellium approximation for the ionic background and the Kohn-Sham mean
field for the electrons. The microscopic origin of SM and its main features
(structure of the mode in light and medium clusters, separation into low- and
high-energy plasmons, coupling high-energy M1 scissors and E2 quadrupole
plasmons, contributions of shape isomers, etc) are discussed. The scissors M1
strength acquires large values with increasing cluster size. The mode is
responsible for the van Vleck paramagnetism of spin-saturated clusters. Quantum
shell effects induce a fragile interplay between Langevin diamagnetism and van
Vleck paramagnetism and lead to a remarkable dia-para anisotropy in magnetic
susceptibility of particular light clusters. Finally, several routes for
observing the SM experimentally are discussed.Comment: 21 pages, 7 figure
Optimal estimation of losses at the ultimate quantum limit with non-Gaussian states
We address the estimation of the loss parameter of a bosonic channel probed
by arbitrary signals. Unlike the optimal Gaussian probes, which can attain the
ultimate bound on precision asymptotically either for very small or very large
losses, we prove that Fock states at any fixed photon number saturate the bound
unconditionally for any value of the loss. In the relevant regime of low-energy
probes, we demonstrate that superpositions of the first low-lying Fock states
yield an absolute improvement over any Gaussian probe. Such few-photon states
can be recast quite generally as truncations of de-Gaussified photon-subtracted
states.Comment: 4 pages, 3 figure
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