Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session H29: Focus Session: Carbon Nanotubes and Related Materials VI: Graphene Transport |
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Sponsoring Units: DMP Chair: Alessandra Lanzara, University of California, Berkeley Room: Morial Convention Center 221 |
Tuesday, March 11, 2008 8:00AM - 8:12AM |
H29.00001: Binary memory switching in zigzag-edge graphene nanostrips Daniel Gunlycke, Denis A. Areshkin, John W. Mintmire, Junwen Li, Carter T. White Owing to a peculiar boundary condition, the ground state of any hydrogen-terminated zigzag-edge graphene nanostrip is predicted to exhibit spin-polarized edge states. We capture this physics in a model which has a Hamiltonian that consists of tight-binding terms and terms describing the potential from a spin-dependent scalar field. The model is solved in the presence of a ballistic current passing through the nanostrip. Studying the grand canonical potential for the system, it is shown that the spin-polarized state collapses above a certain bias. Below that threshold there is a bi-stable regime which could be exploited in a possible memory device. The memory could be both set and cleared through the bias and be read by measuring the current through the device. [Preview Abstract] |
Tuesday, March 11, 2008 8:12AM - 8:24AM |
H29.00002: Graphene and Graphite Nanoribbons: phonon-scattering limit of conductivity from tight-binding Daniel Finkenstadt, Gary Pennington, Michael Mehl To understand nanoribbons of graphene, and multilayers of such ribbons, we developed an ab initio parametrized fit to Carbon and Hydrogen chemical data, out to arbitrary neighbor interactions, including relaxations [\emph{Phys. Rev. B} \textbf{76}, 121405R (2007)]. Our computed band structure shows a decrease in the armchair edge band gap when ribbons are multilayered. Further, the well-known three-family behavior of armchair bangaps is confirmed and shown here to apply also to the drift velocity of charge carriers, which can have $\pm 20$\% deviation from the ideal Fermi velocity. Boltzmann carrier transport simulations from calculated phonon spectra also show a familial dependence of conductance, peak field-effect mobility and ``on'' conductance that increase linearly with ribbon width. We will also discuss phonon-limited scattering of charge carriers in graphene multilayers and the temperature dependence of transport. [Preview Abstract] |
Tuesday, March 11, 2008 8:24AM - 8:36AM |
H29.00003: Spin transport in rough graphene nanoribbons Inanc Adagideli, Michael Wimmer, Savas Berber, David Tomanek, Klaus Richter We investigate spin conductance in zigzag graphene nanoribbons and propose a spin injection method based only on graphene. Combining density functional theory with tight-binding transport calculations, we find that nanoribbons with asymmetrically shaped edges show a non-zero spin conductance and can be used for spin injection. Furthermore, we show that nanoribbons with rough edges exhibit mesoscopic spin conductance fluctuations with a universal value of $\mathrm{rms} G_{\mathrm{s}}\approx 0.4 e/4\pi$. [Preview Abstract] |
Tuesday, March 11, 2008 8:36AM - 9:12AM |
H29.00004: Electron Transport in Graphitic Nanostructures Invited Speaker: Local control of the electrostatic potential in graphene nanostructures can provide a new insight into Dirac fermions in confined geometries in electric and magnetic fields. In this presentation, we report electronic transport measurements in patterned locally gated graphene nanoconstrictions and locally gated single walled carbon nanotubes with tunable transmission and bipolar heterojunctions. We observe various unusual transport phenomena, such as energy gap formation in confined graphene structures and series of fractional quantum Hall conductance plateaus at high magnetic fields as the local charge density is varied in the graphene heterojunction regions.~These observed results can be explained in terms of equilibration of chiral edge states at the heterojunction interfaces, indicating charge polarity dependence of quantum Hall edge state equilibration. ~ [Preview Abstract] |
Tuesday, March 11, 2008 9:12AM - 9:24AM |
H29.00005: ABSTRACT WITHDRAWN |
Tuesday, March 11, 2008 9:24AM - 9:36AM |
H29.00006: Coulomb blockade effects in graphene nanoribbons Fernando Sols, Francisco Guinea, Antonio Castro Neto We propose that recent transport experiments revealing the existence of an energy gap in graphene nanoribbons may be understood in terms of Coulomb blockade. Electron interactions play a decisive role at the quantum dots which form due to the presence of necks arising from the roughness of the graphene edge. With the average transmission as the only fitting parameter, our theory shows good agreement with the experimental data. [Preview Abstract] |
Tuesday, March 11, 2008 9:36AM - 9:48AM |
H29.00007: Distinct Transport Properties of Mono-Layer and Bi-Layer Graphene Nanoribbons Yu-Ming Lin, Zhihong Chen, Phaedon Avouris Graphene holds promise for future electronic applications owing to its exceptional carrier mobility and a Dirac-like, massless dispersion relation for charge carriers. Here we report on experimental studies of electrical transport properties of graphene nano-ribbon devices. Graphene nano-ribbons devices, consisting of mono-layer and bi-layer graphene, were fabricated by e-beam lithography and plasma etching process. These nano-ribbon devices exhibit size-dependent transport properties due to quantum confinement at low temperatures. We observed distinct transport behaviors for mono-layer and bi-layer devices, and this may be related to a tunable bandgap that can be induced in bi-layer graphene. In particular, in bi-layer devices, we observed a significantly lower noise level than that of single-layer graphene. These findings provide insight into the intrinsic noise mechanisms in graphene layers and also elucidate the impact of the coupling between the two layers in the bi-layer graphene on transport properties. [Preview Abstract] |
Tuesday, March 11, 2008 9:48AM - 10:00AM |
H29.00008: Transverse Field Effect in Graphene Nanoribbons Kathryn Todd, Hung-tao Chou, David Goldhaber-Gordon We describe transport measurements on graphene nanoribbon devices with separately addressable side gates. Applying the same voltage to both side gates allows us to resolve the Dirac points in the nanoribbon and in the 2-dimensional graphene leads. In conjunction with the side gates, a back gate allows us to separately tune the nanoribbon and the leads between p-type and n-type. Source-drain measurements illustrate the importance of charging effects in these short nanoribbons. Applying opposing voltages to the two side gates allows us to test predictions about the effect of a transverse electric field in graphene nanoribbons. [Preview Abstract] |
Tuesday, March 11, 2008 10:00AM - 10:12AM |
H29.00009: High-Bias Electronic Transport in Graphene Ribbon Devices Melinda Han, Inanc Meric, Kin Fai Mak, St\'ephane Berciaud, Tony Heinz, Ken Shepard, Philip Kim We present experimental studies of electronic transport in graphene under high electric fields. Graphene ribbon devices with varying widths and lengths are fabricated from mechanically exfoliated single-layer graphene sheets using electron beam lithography followed by oxygen plasma etching. Conductance measurements show a tendency of current saturation under high source-drain bias. In addition, we employ micro-Raman spectroscopy simultaneously with transport measurement on the current carrying device in vacuum. We observe an enhancement of the G-band anti-Stokes/Stokes intensity ratio, where the optical phonon temperature is estimated to be over $\sim $500K before device failure. [Preview Abstract] |
Tuesday, March 11, 2008 10:12AM - 10:24AM |
H29.00010: Graphene zigzag ribbons: hidden multiferroic order and transport J. Fernandez-Rossier, F. Munoz-Rojas, Juan Jose Palacios A new type of electronic phase with coexisting magnetic and ferroelectric order is predicted for graphene ribbons with zigzag edges [1]. The electronic structure of the system is described with a mean field Hubbard model that yields results very similar to those of density functional calculations[2,3]. Without further approximations, the mean field theory is recasted in terms of a BCS wave function for electron-hole pairs in the edge bands. The BCS coherence present in each spin-channel is related to spin-resolved electric polarization. Although the total electric polarization vanishes, due to an internal phase locking of the BCS state, strong magneto-electric effects are expected in this system. We explore these by spin polarized transport across finite length zig-zag ribbons, connected to non-magnetic electrodes [4]. We demonstrate that such system can present very large changes in resistance due to application of lateral electric field that modify the magnetic structure [2,4]. [1] J. Fernandez-Rossier, arXiv:0710.3484 [2] Y. Son, M.L. Cohen, and S. G. Louie, Nature *444*, 347 (2006) [3] J. Fernandez-Rossier and J. J. Palacios, Phys. Rev. Lett. *99*, 177204 (07) [4] J. Fernandez-Rossier, F. Munoz-Rojas, J. J. Palacios, in preparation [Preview Abstract] |
Tuesday, March 11, 2008 10:24AM - 10:36AM |
H29.00011: Rough edges in graphene Vladimir Cvetkovic, Zlatko Tesanovic Recent progress in fabrication of graphene and the understanding of its properties make the graphene a strong contender for a building block of future electronic devices. We analyze the effects of the scattering off rough edges on the transport in graphene nanoribbons. The confinement of the Dirac particles in a nanoribbon is achieved either by means of a large mass term in the Hamiltonian or by imposing boundary conditions appropriate for graphene sheets on the quantum mechanical wave-functions. Variations in the nanoribbon width lead to a nontrivial lateral channel-mixing and provide important limitations to quantum transport. We present a perturbative solution for the problem and derive experimentally measurable conductivity up to the leading order in the case of a nanoribbon with such randomly varying width. [Preview Abstract] |
Tuesday, March 11, 2008 10:36AM - 10:48AM |
H29.00012: Ab initio study of edge functionalization effects on electronic transport through graphene nanoribbons Amir Farajian, Narjes Gorjizadeh, Yoshiyuki Kawazoe We investigate quantum transport through graphene nanoribbons with and without hydrogen saturation. Both armchair-edged and zigzag-edged ribbons with and without hydrogen saturation are considered. For calculating transport properties, we make use of ab initio electronic structure calculations followed by Green's function implementation of the Landauer's formalism. The calculated conductance characteristics show significant dependence on the edge functionalization, i.e., whether or not the armchair and zigzag nanoribbons are saturated by hydrogen atoms. The effects of the carrier spin orientations are also discussed. These results are useful in interpreting the experimental data, and in using functionalized graphene nanoribbons for nanoelectronics and sensor applications. [Preview Abstract] |
Tuesday, March 11, 2008 10:48AM - 11:00AM |
H29.00013: Thermoelectric effects in ballistic graphene ribbons. Eduard Bogachek, Igor Romanovsky, Uzi Landman A theoretical analysis of electrical and thermal transport in ballistic graphene strips and carbon bilayers, connected to electrodes, is presented. Gate voltage and temperature dependences of thermoelectric coefficients and thermoconductance for different ratios of strip lengths and widths are studied both in the linear and nonlinear regime (finite applied voltage and temperature differences). Violation of the Onsager relation between the Peltier and thermopower coefficients in the nonlinear regime is considered. Results obtained for carbon bilayers are compared with those in single layers. The effect of transverse voltage applied between layers on the thermoelectric transport in carbon bilayers is investigated. [Preview Abstract] |
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