Quantum antidot as a controllable spin injector and spin filter

We propose a device based on an antidot embedded in a narrow quantum wire in the edge state regime, that can be used to inject and/or to control spin polarized current. The operational principle of the device is based on the effect of resonant backscattering from one edge state into another through a localized quasi-bound states, combined with the effect of Zeeman splitting of the quasibound states in sufficiently high magnetic field. We outline the device geometry, present detailed quantum-mechanical transport calculation and suggest a possible scheme to test the device performance and functionality

Spin splitting in open quantum dots

We present results from a theoretical and experimental study of spin-splitting in small open lateral quantum dots (i.e. in the regime when the dot is connected to the reservoirs via leads that support one or more propagating modes). We demonstrate that the magnetoconductance shows a pronounced splitting of the conductance peaks (or dips) which persists over a wide range of magnetic fields (from zero field to the edge-state regime) and is virtually independent of magnetic field. A numerical analysis of the conductance and the dot eigenspectrum indicates that this feature is related to a lifting of the spin degeneracy in the corresponding closed dot associated with the interaction between electrons of opposite spin.Comment: 4 pages, 4 figures 1 misdirected figure reference corrected mismatch between spin-up/spin-down notation in figure 3-4 and discussion corrected, clarifications in text adde

Edge disorder induced Anderson localization and conduction gap in graphene nanoribbons

We study the effect of the edge disorder on the conductance of the graphene nanoribbons (GNRs). We find that only very modest edge disorder is sufficient to induce the conduction energy gap in the otherwise metallic GNRs and to lift any difference in the conductance between nanoribbons of different edge geometry. We relate the formation of the conduction gap to the pronounced edge disorder induced Anderson-type localization which leads to the strongly enhanced density of states at the edges, formation of surface-like states and to blocking of conductive paths through the ribbons

Resonant reflection at magnetic barriers in quantum wires

The conductance of a quantum wire containing a single magnetic barrier is studied numerically by means of the recursive Greens function technique. For sufficiently strong and localized barriers, Fano - type reflection resonances are observed close to the pinch-off regime. They are attributed to a magnetoelectric vortex-type quasibound state inside the magnetic barrier that interferes with an extended mode outside. We furthermore show that disorder can substantially modify the residual conductance around the pinch-off regime.Comment: 7 pages, 5 figure

Effect of Spatial Charge Inhomogeneity on 1/f Noise Behavior in Graphene

Scattering mechanisms in graphene are critical to understanding the limits of signal-to-noise-ratios of unsuspended graphene devices. Here we present the four-probe low frequency noise (1/f) characteristics in back-gated single layer graphene (SLG) and bilayer graphene (BLG) samples. Contrary to the expected noise increase with the resistance, the noise for SLG decreases near the Dirac point, possibly due to the effects of the spatial charge inhomogeneity. For BLG, a similar noise reduction near the Dirac point is observed, but with a different gate dependence of its noise behavior. Some possible reasons for the different noise behavior between SLG and BLG are discussed.Comment: 28 pages, 3 figures + 3 supplement figure

You Say Bully, I Say Bullied: School Culture and Definitions of Bullying in Two Elementary Schools

Purpose This chapter examines the definitions of bullying used by students and adults in elementary schools and the effects that these definitions had within the broader school culture. Design/methodology/approach I combine interviews with 53 students and 10 adults and over 430 hours of participant observation with fifth grade students at two rural elementary schools. Findings Definitions of bullying held by those in these schools typically differed from those used by researchers. Even when individuals held definitions that were in line with those used by researchers, however, a focus on identifying bullies rather than on behaviors that fit definitions of bullying contributed to a school culture in which negative interactions were normalized and student reports of these behaviors were discouraged. Research limitations/implications This study is limited to two elementary schools in the rural Midwest and cannot be seen as representative of all schools. Support for my findings from other research combined with similar definitions and school cultures in both schools, however, suggest that these definitions and practices are part of a broader cultural context of bullying in the United States. Practical implications These findings suggest that schools might be better served by focusing less on labels like bully and more on particular behaviors that are to be taken seriously by students, teachers, staff members, and principals. Originality/value Although other researchers have studied definitions of bullying, none have combined these definitions with observational data on the broader school contexts in which those definitions are created and used

Towards a sociocultural understanding of children’s voice

While ‘voice’ is frequently invoked in discussions of pupils’ agency and empowerment, less attention has been paid to the dialogic dynamics of children’s voices and the sociocultural features shaping their emergence. Drawing on linguistic ethnographic research involving recent recordings of ten and eleven year-old children’s spoken language experience across the school day, this article examines how pupils’ voices are configured within institutional interactional contexts which render particular kinds of voice more or less hearable, and convey different kinds of value. Analysis shows how children appropriate and reproduce the authoritative voices of education, popular culture and parents in the course of their induction into social practices. At the same time they also express varying degrees of commitment to these voices and orchestrate their own and other people’s voices within accounts and anecdotes, making voice appropriation an uneven, accumulative process shot through with the dynamics of personal and peer-group experience. The examination of children’s dialogue from different contexts across the school day highlights the situated semiotics of voice and the heteroglossic development of children’s speaking consciousness

Chemically-induced Mobility Gaps in Graphene Nanoribbons: A Route for Upscaling Device Performances

We report a first-principles based study of mesoscopic quantum transport in chemically doped graphene nanoribbons with a width up to 10 nm. The occurrence of quasibound states related to boron impurities results in mobility gaps as large as 1 eV, driven by strong electron-hole asymmetrical backscattering phenomena. This phenomenon opens new ways to overcome current limitations of graphene-based devices through the fabrication of chemically-doped graphene nanoribbons with sizes within the reach of conventional lithography.Comment: Nano Letters (in press