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© 2013 American Physical Society. Work in Madrid was supported by the MICINN (Project No. MAT2010-17180). Research of C.G. was supported by the PICATA postdoctoral fellowship from the Moncloa Campus of International Excellence (UCM-UPM). P.A.O. acknowledges financial support from the FONDECYT (Grant No. 1100560)., We find clear signatures of spin-dependent negative differential resistance in compound systems comprising a graphene nanoribbon and a set of ferromagnetic insulator strips deposited on top of it. The periodic array of ferromagnetic strips induces a proximity exchange splitting of the electronic states in graphene, resulting in the appearance of a superlattice with a spin-dependent energy spectrum. The electric current through the device can be highly polarized and both the current and its polarization manifest nonmonotonic dependence on the bias voltage. The device operates therefore as an Esaki spin diode, which opens possibilities to design new spintronic circuits., MICINN, Moncloa Campus of International Excellence (UCM-UPM), FONDECYT, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 2013 American Physical Society. Work in Madrid was supported by MICINN (Project No. MAT2010-17180). Research of C.G. was supported by a PICATA postdoctoral fellowship from the Moncloa Campus of International Excellence (UCM-UPM). R.P.A.L. would like to thank FAPEAL (Alagoas State Research Agency) via project PRONEX, CNPq, and FINEP (Brazilian Research Agencies) for partial financial support., We study the semiclassical dynamics of interacting electrons in a biased crystal lattice. A complex dynamical scenario emerges from the interplay between the Coulomb and the external electric fields. When the electrons are far apart, the Coulomb potential may be small compared to the external potential and the electrons oscillate with effective Bloch frequencies, determined by the local electric field. In the opposite case, nearby electrons either separate or form a bound pair, depending on the initial energy compared to the band width. The pair due to the Coulomb field is stable even in the absence of the external field., MICINN, PICATA postdoctoral fellowship from the Moncloa Campus of International Excellence (UCM-UPM), FAPEAL, FINEP, CNPq, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 2014 American Physical Society. This work was supported by the DAAD (54367888), by NBRP of China (2012CB921303), by MINECO (Grants No. PRI-AIBDE-2011-0.927 and No. MAT 2010-17180), by NSFChina under Grant No. 11274364, and by PDSF-China under Grant No. 2013M540153. We acknowledge support from the German Excellence Initiative: Cluster of Excellence EXC 1056 “Center for Advancing Electronics Dresden” (cfAED). A.M.G. and E.D. contributed equally to this work., We report on spin transport along double-helical molecular systems by considering various contact configurations and asymmetries between the two helical strands in the regime of completely coherent charge transport. Our results reveal that no spin polarization appears in two-terminal molecular devices when coupled to one-dimensional electrodes. The same holds in the case of finite-width electrodes if there is a bottleneck of one single site in the system electrode-molecule-electrode. Then, additional dephasing is necessary to induce spin-filtering effects. In contrast, nonzero spin polarization is found in molecular devices with multiple terminals or with two finite-width electrodes, each of them connected to more than one site of the molecule. The magnitude of spin polarization can be enhanced by increasing the asymmetry between the two strands. We point out that the spin-filtering effects could emerge in double-helical molecular devices at low temperature without dephasing by a proper choice of the electrode number and the connection between the molecule and the electrodes., MINECO, DAAD, NBRP of China, NSF-China, PDSF-China, cfAED, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 2014 American Physical Society. The authors thank F. Guinea and N. Zinner for helpful comments. This work was supported by MINECO through Grants No. FIS2010-21372 and No. MAT2010-17180, by Comunidad de Madrid through Grant Microseres-CM, and by the EU through Marie Curie ITN NanoCTM. Research of C.G. was supported by a PICATA postdoctoral fellowship from the Moncloa Campus of International Excellence (UCM-UPM)., Two-particle scattering in graphene is a multichannel problem, where the energies of the identical or opposite-helicity channels lie in disjoint energy segments. Due to the absence of Galilean invariance, these segments depend on the total momentum Q. The dispersion relations for the two opposite-helicity scattering channels are analogous to those of two one-dimensional tight-binding lattices with opposite dispersion relations, which are known to easily bind states at their edges. When an s-wave separable interaction potential is assumed, those bound states reveal themselves as three Feshbach resonances in the identical-helicity channel. In the limit Q -> 0, one of the resonances survives and the opposite-helicity scattering amplitudes vanish., Comunidad de Madrid, Ministerio de Economía y Competitividad (MINECO), Unión Europea. FP7, Moncloa Campus de Excelencia Internacional (UCM-UPM), Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 2009 The American Physical Society. Travel between Bayreuth and Madrid is supported by the DAAD-MEC joint program Acciones Integradas. Work at Madrid was supported by MEC (Project MOSAICO) and BSCH-UCM (Project No. PR34/07-15916). R. P. A. L. ac knowledges support by MEC through the Juan de la Cierva program and G. Rowlands for helpful discussions. C. G. acknowledges support by DFG and DAAD, and C. M. acknowledges helpful discussions with Y. Gaididei, We investigate Bloch oscillations of interacting cold atoms in a mean-field framework. In general, atom-atom interaction causes dephasing and destroys Bloch oscillations. Here we show that Bloch oscillations are persistent if the interaction is modulated harmonically with suitable frequency and phase. For other modulations, Bloch oscillations are rapidly damped. We explain this behavior in terms of collective coordinates whose Hamiltonian dynamics permits one to predict a whole family of stable solutions. In order to describe also the unstable cases, we carry out a stability analysis for Bogoliubov excitations. Using Floquet theory, we are able to predict the unstable modes as well as their growth rate, found to be in excellent agreement with numerical simulations., MEC, BSCH-UCM, DFG, DAAD, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© Amer Chemical Soc. The authors thank Ron Naaman for very enlightening discussions on spin-dependent effects in helical systems. This work was supported by the German Academic Exchange Service (DAAD - project reference nr. 54367888) and by Ministerio de Economía y Comptetitividad (MINECO - PRI-AIBDE-2011-0.927) within the joint program Acciones Integradas. Computational resources were provided by the ZIH at TU-Dresden. T.B. thanks the International Max Planck Research School Dynamical Processes in Atoms, Molecules and Solids for financial support. E.D, C.G. and F.D-A were further supported by MINECO (MAT 2010-17180), and research of C.G. was funded by a PICATA postdoctoral fellowship from the Moncloa Campus of International Excellence (UCM-UPM). We gratefully acknowledge support from the German Excellence Initiative via the Cluster of Excellence EXC 1056 ”Center for Advancing Electronics Dresden” (cfAED). This research was partially supported by World Class University program funded by the Ministry of Education, Science and Technology through the National Research Foundation of Korea (R31- 10100)., This study is devoted to a consistent derivation of an effective model Hamiltonian to describe spin transport along a helical pathway and in the presence of spin-orbit interaction, the latter being induced by an external field with helical symmetry. It is found that a sizable spin polarization of an unpolarized incoming state can be obtained without introducing phase breaking processes. For this, at least two energy levels per lattice site in the tight-binding representation are needed. Additionally, asymmetries in the effective electronic-coupling parameters as well as in the spin-orbit interaction strength must be present to achieve net polarization. For a fully symmetric system-in terms of electronic and spin-orbit couplings-no spin polarization is found. The model presented is quite general and is expected to be of interest for the treatment of spin-dependent effects in molecular scale systems with helical symmetry., German Academic Exchange Service (DAAD), Ministerio de Economa y Comptetitividad, International Max Planck Research School Dynamical Processes in Atoms, Molecules and Solids, MINECO, UCM-UPM, Center for Advancing Electronics Dresden (cfAED), Ministry of Education, Science and Technology, National Research Foundation of Korea, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

UTS School of Design researchers were approached by Central Tablelands Landcare and the Biodiversity Conservation Trust to raise awareness of biodiversity conservation among local broadacre farmers, particularly those whose lands are home to significant biodiversity assets. The research team were tasked with helping to build and strengthen relationships with landholders and community stakeholders in the Central Tablelands region and to inspire interest in, and engagement with, biodiversity conservation activities. Beyond this direction, the brief was open, giving the team the opportunity to deploy a range of design research methodologies in service of their project outputs. The work began with a series of design workshop that drew together landholders and interested community members who were part of the Central Tablelands Landcare network. The workshops produced three key findings, priority areas and resulting design principles that researchers used to guide the subsequent outputs. Drawing on research findings, the research team produced two design interventions (described in more detail below): a biodiversity guide to native grasses, and a series of designed objects depicting remarkable local species. These interventions were designed to ‘put people or a community of people at the centre of a guidebook’ by producing a tailored product that spoke to the needs, goals and practices of this particular group of landholders.