Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session W28: Graphene: Nanoribbons and Electronic Transport |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Nancy Sandler, Ohio University Room: C156 |
Thursday, March 24, 2011 11:15AM - 11:27AM |
W28.00001: Low Bias Negative Differential Resistance in Graphene Nanoribbon Superlattices Gerson J. Ferreira, Michael N. Leuenberger, Daniel Loss, J. Carlos Egues We theoretically investigate negative differential resistance (NDR) for ballistic transport in semiconducting armchair graphene nanoribbon superlattices at low bias voltages $V_{SD}$. We combine the modulated graphene-Dirac hamiltonian with the Landauer formalism to calculate the current $I_{SD}$ through the system. This description is expected to be valid at low biases and for narrow samples. We find three distinct transport regimes in which NDR occurs: (i) a ``classical regime'' in which the transport across the crossings of barrier and valley bandgaps is suppressed; (ii) a quantum regime dominated by superlattice miniband conduction, with current suppression arising from the misalignment of miniband states with increasing $V_{SD}$; (iii) a Wannier-Stark ladder regime with current peaks occurring at the crossings of Wannier-Stark rungs from distinct ladders. We emphasize that all the above mechanisms show NDR at voltages lower than 500 mV. Interestingly, within the miniband transport regime the NDR occurs at biases as low as 10 mV, i.e., comparable to the miniband width. [Preview Abstract] |
Thursday, March 24, 2011 11:27AM - 11:39AM |
W28.00002: A finite difference method for transport of massless Dirac fermions: The case of graphene nanoribbons Caio Lewenkopf, Alexis Hernandez We develop a new finite difference scheme to numerically compute the scattering matrix of two-dimensional massless Dirac fermions propagating in a ribbon geometry. The method is nonlocal, avoids the fermion doubling problem, and is suitable for introducing different kinds of boundary conditions. To illustrate its utility we compute the Landauer conductance of a monolayer graphene sheets with zig-zag boundary conditions in presence of a perpendicular magnetic field. The method is particularly useful in the study of long range disorder effects (much larger than the lattice spacing) in large graphene strips. In passing, we also show how the method works in the description of electronic transport at the surface of three-dimensional topological insulators. [Preview Abstract] |
Thursday, March 24, 2011 11:39AM - 11:51AM |
W28.00003: ABSTRACT WITHDRAWN |
Thursday, March 24, 2011 11:51AM - 12:03PM |
W28.00004: Graphene edge from A to Z Yuanyue Liu, Somnath Bhowmick, Boris I. Yakobson We introduce an energy decomposition anzats, which leads to an analytical expression for the edge energy G(X) of arbitrary direction-cut angle X in two dimensional materials [1]. We further show that thermodynamic conditions at the edge simply add a ``chemical phase shift'' C, G(X) = cos(X + C), making the favorable shapes controllable, according to the Wulff construction. Direct atomistic computations and analysis for graphene, as well as 2D boron nitride (h-BN), and zinic oxide (ZnO) support the universal nature of the relationship.\\[4pt] [1] Y. Liu, A. Dobrinsky, and B.I. Yakobson, Phys. Rev. Lett., in press (Dec 10 2010 issue). [Preview Abstract] |
Thursday, March 24, 2011 12:03PM - 12:15PM |
W28.00005: Boron nitride nanoribbons become metallic Alejandro Lopez-Bezanilla, Jingsong Huang, Humberto Terrones, Bobby Sumpter Boron nitride (BN) sheets can be grown on nickel substrates, similar to graphene, and BN domains coexist with graphene. The synthesis of zig-zag BN nanoribbons (zBNNRs) brings interesting possibilities regarding edge chemistry: since both boron and nitrogen atoms are exposed on each edge the functionality of the nanostructure is enriched. We report first principles calculations on the electronic properties of zBNNR nanoribbons with several types of functionalization. Sulfur and oxygen edge doping and topological one-dimensional defects are studied and the possibility of having half metallicity is also analysed. Sulfur and oxygen edge passivation converts zBNNRs into a metallic material which offers several possibilities for new applications in electronics, molecular sensing and spintronics. [Preview Abstract] |
Thursday, March 24, 2011 12:15PM - 12:27PM |
W28.00006: Graphene valley pseudospin filter using an extended line defect Daniel Gunlycke, Carter White Although graphene exhibits excellent electron and thermal transport properties, it does not have an intrinsic band gap, required to use graphene as a replacement material for silicon and other semiconductors in conventional electronics. The band structure of graphene with its two cones near the Fermi level, however, offers opportunities to develop non-traditional applications. One such avenue is to exploit the valley degeneracy in graphene to develop valleytronics. A central component in valleytronics is the valley filter, just as the spin filter is central in spintronics. Herein, we present a two-dimensional valley filter based on scattering of electrons and holes off a recently observed extended line defect [Nat. Nanotech. \textbf{5}, 326 (2010)] within graphene. The transmission probability depends strongly on the valley pseudospin and the angle of incidence of the incident quasiparticles. Quasiparticles arriving at the line defect at a high angle of incidence lead to a valley polarization of the transmitted beam that is near 100 percent. [Preview Abstract] |
Thursday, March 24, 2011 12:27PM - 12:39PM |
W28.00007: Zero Landau level in folded graphene nanoribbons Elsa Prada, Pablo San-Jose, Luis Brey Graphene nanoribbons can be folded into a double layer system keeping the two layers decoupled. In the Quantum Hall regime folds behave as a new type of Hall bar edge. We show that the symmetry properties of the zero Landau level in metallic nanoribbons dictate that the zero energy edge states traversing a fold are perfectly transmitted onto the opposite layer. This result is valid irrespective of fold geometry, magnetic field strength and crystallographic orientation of the nanoribbon. Backscattering suppression on the N=0 Hall plateau is ultimately due to the orthogonality of forward and backward channels, much like in the Klein paradox. [Preview Abstract] |
Thursday, March 24, 2011 12:39PM - 12:51PM |
W28.00008: Effective time-reversal symmetry breaking in the spin relaxation in a graphene quantum dot Philipp Struck, Guido Burkard We study the relaxation of a single electron spin in a circular gate-tunable quantum dot in gapped graphene [1]. Direct coupling of the spin to out-of-plane phonons via the intrinsic spin-orbit coupling leads to a lowered relaxation time $T_1$ at intermediate B-fields. At low fields, $T_1$ increases as $\propto B^{-2}$ due to the suppression of the phonon density of states at long wavelengths in a finite system. We also find that Rashba spin-orbit induced admixture of opposite spin states in combination with the emission of in-plane phonons provides various further relaxation channels via deformation potential and bond-length change. In the absence of valley mixing, spin relaxation takes place within each valley separately and thus time-reversal symmetry is effectively broken, thus inhibiting the van Vleck cancellation at $B=0$ known from GaAs quantum dots. Both the absence of the van Vleck cancellation as well as the out-of-plane phonons lead to a behavior of the spin relaxation rate at low magnetic and intermediate fields which is markedly different from the known results for GaAs. At high fields there is a crossover to $T_1\propto B^{-2}$ or $\propto B^{-4}$.\\[4pt] [1] P. R. Struck and G. Burkard, Phys.\ Rev.\ B \textbf{82}, 125401 (2010). [Preview Abstract] |
Thursday, March 24, 2011 12:51PM - 1:03PM |
W28.00009: Sensory Organ Like Response of Zigzag Edge Graphene Nanoribbons Vijay Shenoy, Somnath Bhowmick Using a continuum Dirac theory, we study the density and spin response of zigzag edge terminated graphene ribbons subjected to edge potentials and Zeeman fields. Our analytical calculations of the density and spin responses of the closed system (fixed particle number) to the static edge fields, show a highly nonlinear Weber-Fechner type behavior where the response depends logarithmically on the edge potential. The dependence of the response on the size of the system (e.g.~width of a nanoribbon) is also uncovered. Zigzag edge graphene nanoribbons, therefore, provide a realization of response of organs such as the eye and ear that obey Weber-Fechner law. We validate our analytical results with tight binding calculations. These results are crucial in understanding important effects of electron-electron interactions in graphene nanoribbons such as edge magnetism etc., and also suggest possibilities for device applications of graphene nanoribbons. \\ Reference: Somnath Bhowmick and Vijay B. Shenoy, {\it Physical Review B}, {\bf 82}. 155448 (2010) [Preview Abstract] |
Thursday, March 24, 2011 1:03PM - 1:15PM |
W28.00010: Transport Through Graphene Surface States Douglas Mason, Eric Heller Of particular interest to models of transport through graphene has been the theoretical prediction of long-lived surface states on zigzag cuts. These states may have a strong influence on transport through finite graphene structures since, unlike infinite nanoribbon surface states, they can absorb and emit electrons traveling through the bulk of the structure. We will be presenting a novel approach to these surface states and postulate on their role in recent transport calculations. [Preview Abstract] |
Thursday, March 24, 2011 1:15PM - 1:27PM |
W28.00011: Quantum charge pumping in graphene nanoribbons Tejinder Kaur, Liliana Arrachea, Nancy Sandler The mechanism to generate DC currents in open-quantum systems by applying local de-phased time-dependent potentials is known as charge pumping. For graphene ribbons, pumping techniques provide an alternative route for current production that overcomes the role of contacts. We have analyzed the properties of zero-bias current through graphene nanoribbons using a tight-binding Hamiltonian description and the Keldysh formalism, which provides the proper description for these systems in the quantum non-equilibrium regime. After reviewing results for quantum pumping in a one-dimensional chain attached to two reservoirs, with two local single-harmonic potentials oscillating in time, we will introduce results for finite-width ribbons of square and graphene lattices. A discussion on the differences in transmission functions and DC currents between these two cases will be presented and the role of edge termination in graphene ribbons will be addressed. [Preview Abstract] |
Thursday, March 24, 2011 1:27PM - 1:39PM |
W28.00012: Electronic properties of graphene nanoflakes: energy gap engineering Carlos Ramos, Eduardo Cifuentes, Romeo de Coss, Edgar Martinez Graphene nanostructures show an energy gap resulting of the finite size, and are of current interest because of the potential applications in electronic devices. Thus, we discuss some recent progress in the synthesis of graphene nanoflakes obtained from the reaction of polyaromatic hydrocarbons. We are presenting ab-initio results for the electronic properties of graphene nanoflakes with a hexagonal-zigzag (HZ) structure and different effective radius (R). The calculations were performed using the Density Functional Theory as implemented in the pseudopotential-LCAO method. We find that the, Kohn-Sham gap decreases with size as R$^{-1}$, while the quasi-particle energy gap follow the R$^{-0.8}$ scaling rule. A formula to evaluate the energy gap of a HZ graphene nanoflake of arbitrary size is provided. This research was supported by Conacyt-M\'exico under Grant No. 83604. [Preview Abstract] |
Thursday, March 24, 2011 1:39PM - 1:51PM |
W28.00013: Electric and Magnetic Field Induced Insulating States in High Quality Bilayer Graphene pnp Junctions Lei Jing, Jairo Velasco, Philip Kratz, Gang Liu, Wenzhong Bao, Marc Bockrat, Chun Ning Lau Band gap opening in bilayer graphene has generated significant interest in both technological application and fundamental research. By applying external electric and magnetic field, we observe an insulating state in our dual-gated bilayer graphene device. In addition, we also observe Quantum Hall plateaus with fractional values of $e^{2}/h$ at large magnetic field, which arises from edge state equilibration at the interface of differentially doped regions, in agreement with theoretical predictions. [Preview Abstract] |
Thursday, March 24, 2011 1:51PM - 2:03PM |
W28.00014: Electron-Hole Asymmetry and Electron-Electron Interaction in Bilayer Graphene K. Zou, X. Hong, J. Zhu We report precision measurements of the effective mass $m$* in high-quality bilayer graphene samples using the temperature dependence of Shubnikov-de Haas oscillation. In the measured density range of 0.7x10$^{12}$/cm$^{2}$ $<$ $n$ $<$ 4.1x10$^{12} $/cm$^ {2}$, both the hole mass $m$*$_{\mathrm{h}}$ and the electron mass $m$*$_ {\mathrm{e}}$ increase with increasing $n$, with $m$*$_{\mathrm {h}}$ being roughly 20-30$\%$ larger than $m$*$_{\mathrm{e}}$ at the same density. We compare our results to tight-binding calculations and provide an accurate determination of several hopping parameters. The measured $m$* is substantially suppressed compared to non- interacting values, demonstrating the importance of electron- electron interaction in bilayer graphene. [Preview Abstract] |
Thursday, March 24, 2011 2:03PM - 2:15PM |
W28.00015: Magneto-transport study of band structure of tri-layer graphene Ryuta Yagi, Seiya Fukada, Midor Shimomura We have studied magneto-transport of high-quality tri-layer graphene samples. It has been observed Shubnikov-de Haas oscillations with two different frequencies that corresponded to two bands in tri-layer graphene. Detailed analysis of gate voltage dependence of the frequencies showed that sum of the carrier density for each band gave approximately the nominal carrier density tuned by the gate voltage. From temperature dependence of magnitude of the oscillation we have estimated cyclotron masses. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2025 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700