Since the experimental discovery of magnetic skyrmions achieved one decade ago 1 , there have been significant efforts to bring the virtual particles into all-electrical fully functional devices, inspired by their fascinating physical and topological properties suitable for future low-power electronics 2 . Here, we experimentally demonstrate such a deviceelectrically-operating skyrmion-based artificial synaptic device designed for neuromorphic computing. We present that controlled current-induced creation, motion, detection and deletion of skyrmions in ferrimagnetic multilayers can be harnessed in a single device at room temperature to imitate the behaviors of biological synapses. Using simulations, we demonstrate that such skyrmion-based synapses could be used to perform neuromorphic pattern-recognition computing using handwritten recognition data set, reaching to the accuracy of ~89%, comparable to the software-based training accuracy of ~94%. Chip-level simulation then highlights the potential of skyrmion synapse compared to existing technologies. Our findings experimentally illustrate the basic concepts of skyrmion-based fully functional electronic devices while providing a new building block in the emerging field of spintronics-based bio-inspired computing.

SummaryThe bacterium Burkholderia glumae causes rice grain rot by producing toxoflavin, whose expression is regulated by quorum sensing (QS). We report a major deviation from the current paradigm for the regulation of bacterial polar flagellum genes. The N-octanoyl homoserine lactone (C8-HSL)-deficient mutant of B. glumae is aflagellate and has lost the ability to swim and swarm at 37°C. Mutagenesis of the bacterium with the mini-Tn5rescue identified an IclR-type transcriptional regulator, called QsmR, which is important for flagellum formation. TofR, which is a cognate C8-HSL receptor, activated qsmR expression by binding directly to the qsmR promoter region. From the flagellum gene cluster, we identified flhDC homologues that are directly activated by QsmR. FlhDC in turn activates the expression of genes involved in flagellum biosynthesis, motor functions and chemotaxis in B. glumae. Non-motile qsmR, fliA and flhDC mutants produced toxoflavin, but lost pathogenicity for rice. The unexpected discovery of FlhDC in a polarly flagellate bacterium suggests that exceptions to the typical regulatory mechanisms of flagellum genes exist in Gram-negative bacteria. The finding that functional flagella play critical roles in the pathogenicity of B. glumae suggests that either QS or flagellum formation constitutes a good target for the control of rice grain rot.

Structure of the spin-orbit coupling varies from material to material and thus finding the correct spin-orbit coupling structure is an important step towards advanced spintronic applications. We show theoretically that the curvature in a carbon nanotube generates two types of the spin-orbit coupling, one of which was not recognized before. In addition to the topological phase-related contribution of the spin-orbit coupling, which appears in the off-diagonal part of the effective Dirac Hamiltonian of carbon nanotubes, there is another contribution that appears in the diagonal part. The existence of the diagonal term can modify spin-orbit coupling effects qualitatively, an example of which is the electron-hole asymmetric spin splitting observed recently, and generate four qualitatively different behavior of energy level dependence on parallel magnetic field. It is demonstrated that the diagonal term applies to a curved graphene as well. This result should be valuable for spintronic applications of graphitic materials.Comment: 6 pages, 4 figures, to be published on Physical Review

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The study of spin-related phenomena in materials requires knowledge of the precise form of effective spin-orbit coupling for conducting carriers in solid-states systems. We demonstrate theoretically that curvature induced by corrugations or periodic ripples in single-layer graphenes generates two types of effective spin-orbit couplings. In addition to the spin-orbit coupling reported previously that couples with sublattice pseudospin and corresponds to the Rashba-type spin-orbit coupling in a corrugated single-layer graphene, there is an additional spin-orbit coupling that does not couple with the pseudospin, which can not be obtained from the extension of the curvature-induced spin-orbit coupling of carbon nanotubes. Via numerical calculation we show that both types of the curvature-induced spin-orbit coupling make the same order of contribution to spin relaxation in chemically clean single-layer graphene with nanoscale corrugation. The spin relaxation dependence on the corrugation roughness is also studied. arXiv:1108.6128v3 [cond-mat.mes-hall]