2,160 research outputs found
Helicoidal Fields and Spin Polarized Currents in CNT-DNA Hybrids
We report on theoretical studies of electronic transport in the archetypical
molecular hybrid formed by DNA wrapped around single-walled carbon nanotubes
(CNTs). Using a Green's function formalism in a -orbital tight-binding
representation, we investigate the role that spin-orbit interactions play on
the CNT in the case of the helicoidal electric field induced by the polar
nature of the adsorbed DNA molecule. We find that spin polarization of the
current can take place in the absence of magnetic fields, depending strongly on
the direction of the wrapping and length of the helicoidal field. These
findings open new routes for using CNTs in spintronic devices.Comment: 4 pages, 5 figure
Zebrafish as animal model for aquaculture nutrition research.
The aquaculture industry continues to promote the diversification of ingredients used in aquafeed in order to achieve a more sustainable aquaculture production system. The evaluation of large numbers of diets in aquaculture species is costly and requires time-consuming trials in some species. In contrast, zebrafish (Danio rerio) can solve these drawbacks as an experimental model, and represents an ideal organism to carry out preliminary evaluation of diets. In addition, zebrafish has a sequenced genome allowing the efficient utilization of new technologies, such as RNA-sequencing and genotyping platforms to study the molecular mechanisms that underlie the organism's response to nutrients. Also, biotechnological tools like transgenic lines with fluorescently labeled neutrophils that allow the evaluation of the immune response in vivo, are readily available in this species. Thus, zebrafish provides an attractive platform for testing many ingredients to select those with the highest potential of success in aquaculture. In this perspective article aspects related to diet evaluation in which zebrafish can make important contributions to nutritional genomics and nutritional immunity are discussed
Polarization and Aharonov-Bohm oscillations in quantum-ring magnetoexcitons
We study interaction and radial polarization effects on the the absorption
spectrum of neutral bound magnetoexcitons confined in quantum-ring structures.
We show that the size and orientation of the exciton's dipole moment, as well
as the interaction screening, play important roles in the Aharonov-Bohm
oscillations. In particular, the excitonic absorption peaks display A-B
oscillations both in position and amplitude for weak electron-hole interaction
and large radial polarization. The presence of impurity scattering induces
anticrossings in the exciton spectrum, leading to a modulation in the
absorption strength. These properties could be used in experimental
investigations of the effect in semiconductor quantum-ring structures.Comment: Updated version, 6 pages, 4 figures. To appear in Phys. Rev.
Impurity-enhanced Aharonov-Bohm effect in neutral quantum-ring magnetoexcitons
We study the role of impurity scattering on the photoluminescence (PL)
emission of polarized magnetoexcitons. We consider systems where both the
electron and hole are confined on a ring structure (quantum rings) as well as
on a type-II quantum dot. Despite their neutral character, excitons exhibit
strong modulation of energy and oscillator strength in the presence of magnetic
fields. Scattering impurities enhance the PL intensity on otherwise "dark"
magnetic field windows and non-zero PL emission appears for a wide magnetic
field range even at zero temperature. For higher temperatures, impurity-induced
anticrossings on the excitonic spectrum lead to unexpected peaks and valleys on
the PL intensity as function of magnetic field. Such behavior is absent on
ideal systems and can account for prominent features in recent experimental
results.Comment: 7 pages, 7 figures, RevTe
Tunable pseudogap Kondo effect and quantum phase transitions in Aharonov-Bohm interferometers
We study two quantum dots embedded in the arms of an Aharonov-Bohm ring
threaded by a magnetic flux. The system can be described by an effective
one-impurity Anderson model with an energy- and flux-dependent density of
states. For specific values of the flux, this density of states vanishes at the
Fermi energy, yielding a controlled realization of the pseudogap Kondo effect.
The conductance and transmission phase shifts reflect a nontrivial interplay
between wave interference and interactions, providing clear signatures of
quantum phase transitions between Kondo and non-Kondo ground states.Comment: Published versio
Spin filtering in nanowire directional coupler
The spin transport characteristics of a nanowire directional electronic
coupler have been evaluated theoretically via a transfer matrix approach. The
application of a gate field in the region of mixing allows for control of spin
current through the different leads of the coupler via the Rashba spin-orbit
interaction. The combination of spin-orbit interaction and applied gate
voltages on different legs of the coupler give rise to a controllable
modulation of the spin polarization. Both structural factors and field strength
tuning lead to a rich phenomenology that could be exploited in spintronic
devices.Comment: 9 pages, 4 figure
Landau level mixing by full spin-orbit interactions
We study a two-dimensional electron gas in a perpendicular magnetic field in
the presence of both Rashba and Dresselhaus spin-orbit interactions. Using a
Bogoliubov transformation we are able to write an approximate formula for the
Landau levels, thanks to the simpler form of the resulting Hamiltonian. The
exact numerical calculation of the energy levels, is also made simpler by our
formulation. The approximate formula and the exact numerical results show
excellent agreement for typical semiconductors, especially at high magnetic
fields. We also show how effective Zeeman coupling is modified by spin-orbit
interactions.Comment: 5 pages, 5 figure
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