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 format, tarred, compressed and uuencoded Postscrip

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, $\Omega \lesssim \Gamma/\hbar$, 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