8,792 research outputs found
Light-emitting current of electrically driven single-photon sources
The time-dependent tunnelling current arising from the electron-hole
recombination of exciton state is theoretically studied using the
nonequilibrium Green's function technique and the Anderson model with two
energy levels. The charge conservation and gauge invariance are satisfied in
the tunnelling current. Apart from the classical capacitive charging and
discharging behavior, interesting oscillations superimpose on the tunnelling
current for the applied rectangular pulse voltage.Comment: 14 pages, 5 figure
Proposal for a correlation induced spin-current polarizer
We propose a spin polarizer device composed of a quantum dot connected to the
spin polarized leads. The spin control of the current flowing through the
device is entirely due to the Coulomb interactions present inside the dot. We
show that the initial polarization present in the source lead can be reverted
or suppressed just by manipulating the gate voltage acting on the dot, the
presence of the external magnetic field is not required. The influence of the
temperature and finite bias on the efficiency of the current spin switching
effect is also discussed.Comment: 5 pages, 4 figures, title changed, rearranged figures, one reference
added, discussion extension, accepted for Phys. Rev.
Modulation of the dephasing time for a magnetoplasma in a quantum well
We investigate the femtosecond kinetics of optically excited 2D
magneto-plasma. We calculate the femtosecond dephasing and relaxation kinetics
of the laser pulse excited magneto-plasma due to bare Coulomb potential
scattering, because screening is under these conditions of minor importance. By
taking into account four Landau subbands in both the conduction band and the
valence band, we are now able to extend our earlier study [Phys. Rev. B {\bf
58}, 1998,in print (see also cond-mat/9808073] to lower magnetic fields. We can
also fix the magnetic field and change the detuning to further investigate the
carrier density-dependence of the dephasing time. For both cases, we predict
strong modulation in the dephasing time.Comment: RevTex, 3 figures, to be published in Solid. Stat. Commu
Non-equilibrium current and electron pumping in nanostructures
We discuss a numerical method to study electron transport in mesoscopic
devices out of equilibrium. The method is based on the solution of operator
equations of motion, using efficient Chebyshev time propagation techniques. Its
peculiar feature is the propagation of operators backwards in time. In this way
the resource consumption scales linearly with the number of states used to
represent the system. This allows us to calculate the current for
non-interacting electrons in large one-, two- and three-dimensional lead-device
configurations with time-dependent voltages or potentials. We discuss the
technical aspects of the method and present results for an electron pump device
and a disordered system, where we find transient behaviour that exists for a
very long time and may be accessible to experiments.Comment: 4 pages, 3 figures. Contribution to the International Conference on
Magnetism (ICM) 2009 in Karlsruh
Extreme morphologies of mantis shrimp larvae
Larvae of stomatopods (mantis shrimps) are generally categorized into four larval types: antizoea, pseudozoea (both representing early larval stages), alima and erichthus (the latter two representing later larval stages). These categories, however, do not reflect the existing morphological diversity of stomatopod larvae, which is largely unstudied. We describe here four previously unknown larval types with extreme morphologies. All specimens were found in the collections of the Zoological Museum, University of Copenhagen and were collected during the Danish Dana Expedition round the world 1928-30. These new larval types all represent erichthus-type larvae, especially differing in their shield morphologies. The shield morphology ranges from almost spherical to rather disc-like, with sometimes extremely elongated spines, but only a general systematic assignment of the larvae was possible. Further investigations of these larvae are crucial to understand their life habits and ecological impact, especially as stomatopod and other crustacean larvae might have a much more important position in the marine ecosystems than their corresponding adults
The anomalous Hall conductivity due to the vector spin chirality
We study theoretically the anomalous Hall effect due to the vector spin
chirality carried by the local spins in the - model. We will show that
the vector spin chirality indeed induces local Hall effect in the presence of
the electron spin polarization, while the global Hall effect vanishes if
electron transport is homogeneous. This anomalous Hall effect can be
interpreted in terms of the rotational component of the spin current associated
with the vector chirality.Comment: 12 pages, 5 figure
Nonthermal steady states after an interaction quench in the Falicov-Kimball model
We present the exact solution of the Falicov-Kimball model after a sudden
change of its interaction parameter using non-equilibrium dynamical mean-field
theory. For different interaction quenches between the homogeneous metallic and
insulating phases the system relaxes to a non-thermal steady state on time
scales on the order of hbar/bandwidth, showing collapse and revival with an
approximate period of h/interaction if the interaction is large. We discuss the
reasons for this behavior and provide a statistical description of the final
steady state by means of generalized Gibbs ensembles.Comment: 4 pages, 2 figures; published versio
Twisted-light-induced optical transitions in semiconductors: Free-carrier quantum kinetics
We theoretically investigate the interband transitions and quantum kinetics
induced by light carrying orbital angular momentum, or twisted light, in bulk
semiconductors. We pose the problem in terms of the Heisenberg equations of
motion of the electron populations, and inter- and intra-band coherences. Our
theory extends the free-carrier Semiconductor Bloch Equations to the case of
photo-excitation by twisted light. The theory is formulated using cylindrical
coordinates, which are better suited to describe the interaction with twisted
light than the usual cartesian coordinates used to study regular optical
excitation. We solve the equations of motion in the low excitation regime, and
obtain analytical expressions for the coherences and populations; with these,
we calculate the orbital angular momentum transferred from the light to the
electrons and the paramagnetic and diamagnetic electric current densities.Comment: 11 pages, 3 figure
Excitation Induced Dephasing in Semiconductor Quantum Dots
A quantum kinetic theory is used to compute excitation induced dephasing in
semiconductor quantum dots due to the Coulomb interaction with a continuum of
states, such as a quantum well or a wetting layer. It is shown that a frequency
dependent broadening together with nonlinear resonance shifts are needed for a
microscopic explanation of the excitation induced dephasing in such a system,
and that excitation induced dephasing for a quantum-dot excitonic resonance is
different from quantum-well and bulk excitons.Comment: 6 pages, 4 figures. Extensively revised text, two figures change
Non-equilibrium GW approach to quantum transport in nano-scale contacts
Correlation effects within the GW approximation have been incorporated into
the Keldysh non-equilibrium transport formalism. We show that GW describes the
Kondo effect and the zero-temperature transport properties of the Anderson
model fairly well. Combining the GW scheme with density functional theory and a
Wannier function basis set, we illustrate the impact of correlations by
computing the I-V characteristics of a hydrogen molecule between two Pt chains.
Our results indicate that self-consistency is fundamental for the calculated
currents, but that it tends to wash out satellite structures in the spectral
function.Comment: 5 pages, 4 figure
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