285 research outputs found
Magnetic AC control of the spin textures in a helical Luttinger liquid
We demonstrate the possibility to induce and control peculiar spin textures
in a helical Luttinger liquid, by means of a time-dependent magnetic scatterer.
The presence of a perturbation that breaks the time-reversal symmetry opens a
gap in the spectrum, inducing single-particle backscattering and a peculiar
spin response. We show that in the weak backscattering regime asymmetric spin
textures emerge at the left and right side of the scatterer, whose spatial
oscillations are controlled by the ratio between the magnetization frequency
and the Fermi energy and by the electron interaction. This peculiar spin
response marks a strong difference between helical and non-helical liquids,
which are expected to produce symmetric spin textures even in the AC regime.Comment: 7 pages, 4 figure
Generating and controlling spin-polarized currents induced by a quantum spin Hall antidot
We study an electrically controlled quantum spin Hall antidot embedded in a
two-dimensional topological insulating bar. Helical edge states around the
antidot and along the edges of the bar are tunnel coupled. The close connection
between spin and chirality, typical of helical systems, allows to generate a
spin-polarized current flowing across the bar. This current is studied as a
function of the external voltages, by varying the asymmetry between the
barriers. For asymmetric setups, a switching behavior of the spin current is
observed as the bias is increased, both in the absence and in the presence of
electron interactions. This device allows to generate and control the
spin-polarized current by simple electrical means.Comment: 7 pages, 6 figure
Coulomb blockade microscopy of spin density oscillations and fractional charge in quantum spin Hall dots
We evaluate the spin density oscillations arising in quantum spin Hall
quantum dots created via two localized magnetic barriers. The combined presence
of magnetic barriers and spin-momentum locking, the hallmark of topological
insulators, leads to peculiar phenomena: a half-integer charge is trapped in
the dot for antiparallel magnetization of the barriers, and oscillations appear
in the in-plane spin density, which are enhanced in the presence of electron
interactions. Furthermore, we show that the number of these oscillations is
determined by the number of particles inside the dot, so that the presence or
the absence of the fractional charge can be deduced from the in-plane spin
density. We show that when the dot is coupled with a magnetized tip, the
spatial shift induced in the chemical potential allows to probe these peculiar
features.Comment: 6 pages, 6 figure
Non-equilibrium effects on charge and energy partitioning after an interaction quench
Charge and energy fractionalization are among the most intriguing features of
interacting onedimensional fermion systems. In this work we determine how these
phenomena are modified in the presence of an interaction quench. Charge and
energy are injected into the system suddenly after the quench, by means of
tunneling processes with a non-interacting one-dimensional probe. Here, we
demonstrate that the system settles to a steady state in which the charge
fractionalization ratio is unaffected by the pre-quenched parameters. On the
contrary, due to the post-quench nonequilibrium spectral function, the energy
partitioning ratio is strongly modified, reaching values larger than one. This
is a peculiar feature of the non-equilibrium dynamics of the quench process and
it is in sharp contrast with the non-quenched case, where the ratio is bounded
by one.Comment: 12 pages, 4 figure
Asymmetric Franck-Condon factors in suspended carbon nanotube quantum dots
Electronic states and vibrons in carbon nanotube quantum dots have in general
different location and size. As a consequence, the conventional
Anderson-Holstein model, coupling vibrons to the dot total charge only, may no
longer be appropriated in general. Here we explicitly address the role of the
spatial fluctuations of the electronic density, yielding space-dependent
Franck-Condon factors. We discuss the consequent marked effects on transport
which are compatible with recent measurements. This picture can be relevant for
tunneling experiments in generic nano-electromechanical systems.Comment: 4+ pages, 3 figures (2 color, 1 BW
Small Groups of Galaxies: a Clue to a Critical Universe
We study the formation and the evolution of galaxy groups in a critical
universe, showing the importance of secondary infall for their dynamical
evolution. Merging is only slightly accelerated if galaxies have massive halos,
because the mass initially associated to the individual galaxies is soon
tidally stripped. Stripping is particularly effective for infalling galaxies,
which thus avoid merging. We find that, as a rule, merging is effectively
terminated when infall becomes dominant. We look for compact groups in our
ensemble of simulations, and compare their statistical properties with
Hickson's compact groups. We then discuss in terms of the Press & Schechter
formalism the statistics of such groups and their evolution in different
cosmological scenarios. We show that compact group formation is an ongoing and
frequent process in a critical universe. Our model reconciles the contradiction
between the observed absence of young merger remnants and the high rate of
galaxy interactions expected in compact groups. In open universes, instead,
earlier formation of groups and suppression of secondary infall makes it more
unlikely that compact groups survive as such until the present. We conclude
that the existence of dense and dynamically young groups of galaxies like HCGs
points towards a high-density universe.Comment: 15 pages + 7 figures, accepted by the Astrophysical Journal. AASTEX
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Non-adiabatic pumping through interacting quantum dots
We study non-adiabatic two-parameter charge and spin pumping through a
single-level quantum dot with Coulomb interaction. For the limit of weak tunnel
coupling and in the regime of pumping frequencies up to the tunneling rates,
, we perform an exact resummation of
contributions of all orders in the pumping frequency. As striking non-adiabatic
signatures, we find frequency-dependent phase shifts in the charge and spin
currents, which allow for an effective single-parameter pumping as well as pure
spin without charge currents.Comment: 4 pages, 2 figure
EcR-B1 and Usp nuclear hormone receptors regulate expression of the VM32E eggshell gene during Drosophila oogenesis
AbstractEcdysone signaling plays key roles in Drosophila oogenesis, as its activity is required at multiple steps during egg chamber maturation. Recently, its involvement has been reported on eggshell production by controlling chorion gene transcription and amplification. Here, we present evidence that ecdysone signaling also controls the expression of the eggshell gene VM32E, whose product is a component of vitelline membrane and endochorion layers. Specifically blocking the function of the different Ecdysone receptor (EcR) isoforms we demonstrate that EcR-B1 is responsible for ecdysone-mediated VM32E transcriptional regulation. Moreover, we show that the EcR partner Ultraspiracle (Usp) is also necessary for VM32E expression. By analyzing the activity of specific VM32E regulatory regions in usp2 clones we identify the promoter region mediating ecdysone-dependent VM32E expression. By in vitro binding assay and site-directed mutagenesis we demonstrate that this region contains a Usp binding site necessary for VM32E regulation.Our results further support the crucial role of ecdysone signaling in controlling transcription of eggshell structural genes and suggest that the heterodimeric complex EcR-B1/Usp mediates the ecdysone-dependent VM32E transcriptional activation in the main body follicle cells
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