6,119 research outputs found
Graphene-based spin-pumping transistor
We demonstrate with a fully quantum-mechanical approach that graphene can
function as gate-controllable transistors for pumped spin currents, i.e., a
stream of angular momentum induced by the precession of adjacent
magnetizations, which exists in the absence of net charge currents.
Furthermore, we propose as a proof of concept how these spin currents can be
modulated by an electrostatic gate. Because our proposal involves nano-sized
systems that function with very high speeds and in the absence of any applied
bias, it is potentially useful for the development of transistors capable of
combining large processing speeds, enhanced integration and extremely low power
consumption
Graphene as a non-magnetic spin-current lens
In spintronics, the ability to transport magnetic information often depends
on the existence of a spin current traveling between two different magnetic
objects acting as source and probe. A large fraction of this information never
reaches the probe and is lost because the spin current tends to travel
omni-directionally. We propose that a curved boundary between a gated and a
non-gated region within graphene acts as an ideal lens for spin currents
despite being entirely of non-magnetic nature. We show as a proof of concept
that such lenses can be utilized to redirect the spin current that travels away
from a source onto a focus region where a magnetic probe is located, saving a
considerable fraction of the magnetic information that would be otherwise lost.Comment: 9 pages, 3 figure
Steady-state entanglement between distant quantum dots in photonic crystal dimers
We show that two spatially separated semiconductor quantum dots under
resonant and continuous-wave excitation can be strongly entangled in the
steady-state, thanks to their radiative coupling by mutual interaction through
the normal modes of a photonic crystal dimer. We employ a quantum master
equation formalism to quantify the steady-state entanglement by calculating the
system {\it negativity}. Calculations are specified to consider realistic
semiconductor nanostructure parameters for the photonic crystal dimer-quantum
dots coupled system, determined by a guided mode expansion solution of Maxwell
equations. Negativity values of the order of 0.1 ( of the maximum value)
are shown for interdot distances that are larger than the resonant wavelength
of the system. It is shown that the amount of entanglement is almost
independent of the interdot distance, as long as the normal mode splitting of
the photonic dimer is larger than their linewidths, which becomes the only
requirement to achieve a local and individual qubit addressing. Considering
inhomogeneously broadened quantum dots, we find that the steady-state
entanglement is preserved as long as the detuning between the two quantum dot
resonances is small when compared to their decay rates. The steady-state
entanglement is shown to be robust against the effects of pure dephasing of the
quantum dot transitions. We finally study the entanglement dynamics for a
configuration in which one of the two quantum dots is initially excited and
find that the transient negativity can be enhanced by more than a factor of two
with respect to the steady-state value. These results are promising for
practical applications of entangled states at short time scales.Comment: 10 pages, 7 figure
Métodos de avaliação das condições hÃdricas das plantas.
O funcionamento normal das células demanda condições hÃdricas próximas da saturação, entretanto, essas condições não ocorrem e a célula encontra-se insaturada. O teor de água nas diferentes partes da planta pode variar enormemente. O armazenamento de água na planta é regido pelos fenômenos de interação da água com a planta. As condições hÃdricas nos tecidos das plantas podem ser avaliadas tanto pelo teor como pela energia livre da água e podem ser inferidas por métodos indiretos, como a temperatura das folhas. Pode-se avaliar o teor de água nas plantas r o potencial da água na célula, tecido ou órgão - avaliação com câmara de pressão Scholander. A resistência difusiva estomática pode ser avaliada através de quatro métodos: fluxo de massa, difusão de vapor, manutenção de fluxo, estado de equilÃbrio, temperatura foliar (uso de termômetro de infravermelho).bitstream/CNPAF-2009-09/27961/1/comt_161.pd
Carbon nanotube: a low-loss spin-current waveguide
We demonstrate with a quantum-mechanical approach that carbon nanotubes are
excellent spin-current waveguides and are able to carry information stored in a
precessing magnetic moment for long distances with very little dispersion and
with tunable degrees of attenuation. Pulsed magnetic excitations are predicted
to travel with the nanotube Fermi velocity and are able to induce similar
excitations in remote locations. Such an efficient way of transporting magnetic
information suggests that nanotubes are promising candidates for memory devices
with fast magnetization switchings
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