102 research outputs found
Pedestrian index theorem a la Aharonov-Casher for bulk threshold modes in corrugated multilayer graphene
Zero-modes, their topological degeneracy and relation to index theorems have
attracted attention in the study of single- and bilayer graphene. For
negligible scalar potentials, index theorems explain why the degeneracy of the
zero-energy Landau level of a Dirac hamiltonian is not lifted by gauge field
disorder, for example due to ripples, whereas other Landau levels become
broadened by the inhomogenous effective magnetic field. That also the bilayer
hamiltonian supports such protected bulk zero-modes was proved formally by
Katsnelson and Prokhorova to hold on a compact manifold by using the
Atiyah-Singer index theorem. Here we complement and generalize this result in a
pedestrian way by pointing out that the simple argument by Aharonov and Casher
for degenerate zero-modes of a Dirac hamiltonian in the infinite plane extends
naturally to the multilayer case. The degeneracy remains, though at nonzero
energy, also in the presence of a gap. These threshold modes make the spectrum
asymmetric. The rest of the spectrum, however, remains symmetric even in
arbitrary gauge fields, a fact related to supersymmetry. Possible benefits of
this connection are discussed.Comment: 6 pages, 2 figures. The second version states now also in words that
the conjugation symmetry that in the massive case gets replaced by
supersymmetry is the chiral symmetry. Changes in figure
Coexistence of electron and hole transport in graphene
When sweeping the carrier concentration in monolayer graphene through the
charge neutrality point, the experimentally measured Hall resistivity shows a
smooth zero crossing. Using a two- component model of coexisting electrons and
holes around the charge neutrality point, we unambiguously show that both types
of carriers are simultaneously present. For high magnetic fields up to 30 T the
electron and hole concentrations at the charge neutrality point increase with
the degeneracy of the zero-energy Landau level which implies a quantum Hall
metal state at \nu=0 made up by both electrons and holes.Comment: 5 pages, 6 figure
Video Use and the Student Learning Experience in Politics and International Relations
This article explores video use and the student learning experience in Politics and International Relations (IR). The study brings together and builds on two extant literatures – on deep learning and visual literacy – in order to explore how students make use of three types of video: lecture summaries, current affairs clips and fictional television. Questionnaire and focus group data generate a nuanced picture, with distinct implications for the learning experience. The article shows how different types of video can be linked to the development of different skills for different students
1/f noise in magnetic Ni80Fe20 single layers and Ni80Fe20/Cu multilayers
We have investigated the room temperature 1/f noise of microstructured soft magnetic Ni80Fe20 films, showing the anisotropic magnetoresistance effect, and of Ni80Fe20/Cu magnetic multilayers, showing the giant magnetoresistance effect. We find that the 1/f noise in magnetic multilayers is considerably enhanced with respect to the noise of the single domain layer, which sets a limit on the usability of giant magnetoresistance materials for low-frequency applications
Influence of SiO2 micro-particles onto microstructure, mechanical properties and wear resistance of uhmwpe based composite under dry sliding friction
Operation is demonstrated of a field-effect transistor made of transparant oxidic thin films, showing an intrinsic memory function due to the usage of a ferroelectric insulator. The device consists of a high mobility Sb-doped n-type SnO2 semiconductor layer, PbZr0.2Ti0.8O3 as a ferroelectric insulator, and SrRuO3 as a gate electrode, each layer prepared by pulsed laser deposition. The hysteresis behavior of the channel conductance is studied. Using gate voltage pulses of 100 µs duration and a pulse height of ±3 V, a change of a factor of two in the remnant conductance is achieved. The dependence of the conductance on the polarity of the gate pulse proves that the memory effect is driven by the ferroelectric polarization. The influence of charge trapping is also observed and discussed. © 1996 American Institute of Physics
Tilted-Cone Induced Cusps and Nonmonotonic Structures in Dynamical Polarization Function of Massless Dirac Fermions
The polarization function of electrons with the tilted Dirac cone found in
organic conductors is studied using the tilted Weyl equation. The dynamical
property is explored based on the analytical treatment of the particle-hole
excitation. It is shown that the polarization function as the function of both
the frequency and the momentum exhibits cusps and nonmonotonic structures. The
polarization function depends not only on the magnitude but also the direction
of the external momentum. These properties are characteristic of the tilted
Dirac cone, and are contrast to the isotropic case of grapheme. Further, the
results are applied to calculate the optical conductivity, the plasma frequency
and the screening of Coulomb interaction, which are also strongly influenced by
the tilted cone.Comment: 28 pages, 12 figures, to be published in Journal of the Physical
Society of Japan Vol. 79 (2010) No. 1
Towards Graphene Nanoribbon-based Electronics
The successful fabrication of single layer graphene has greatly stimulated
the progress of the research on graphene. In this article, focusing on the
basic electronic and transport properties of graphene nanoribbons (GNRs), we
review the recent progress of experimental fabrication of GNRs, and the
theoretical and experimental investigations of physical properties and device
applications of GNRs. We also briefly discuss the research efforts on the spin
polarization of GNRs in relation to the edge states.Comment: 9pages,10figure
Students’ Motivation for Learning in Virtual Learning Environments
The specific characteristics of online education require of the student engagement and autonomy, factors which are related to motivation for learning. This study investigated students’ motivation in virtual learning environments (VLEs). For this, it used the Teaching and Learning Strategy and Motivation to Learn Scale in Virtual Learning Environments (TLSM-VLE). The scale presented 32 items and six dimensions, three of which aimed to measure the variables of autonomous motivation, controlled motivation, and demotivation. The participants were 572 students from the Brazilian state of Paraná, enrolled on higher education courses on a continuous education course. The results revealed significant rates for autonomous motivational behavior. It is considered that the results obtained may provide contributions for the educators and psychologists who work with VLEs, leading to further studies of the area providing information referent to the issue investigated in this study
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