Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session P26: Focus Session: Graphene VIII: Electronic Properties |
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Sponsoring Units: DMP Chair: Michael Fuhrer, University of Maryland Room: 328 |
Wednesday, March 18, 2009 8:00AM - 8:12AM |
P26.00001: Experimental studies of the transport in graphene in a parallel magnetic field at low temperatures Liyuan Zhang, Jorge Camacho, Helin Cao, Isaac Childres, Yong Chen, Alexei Tsvelik, Dmitri Kharzeev, Maxim Khodas, Myron Strongin, Tonica Valla, Igor Zaliznyak Graphene has remarkable electric properties, and it is also a very promising material for spintronic applications. Most previous experiments, however, were focused on studying graphene devices in perpendicular magnetic field, which quantizes the real-space motion of Dirac electrons in graphene and leads to an unusual quantum Hall effect. Here we will present the results of experimental studies of electric transport in single- and few-layer graphene devices in parallel magnetic field and at low temperatures. The Dirac-point resistance of our graphene devices~was studied as a function of magnetic field and temperature. The effect of tuning the chemical potential under different magnetic fields was also investigated and will be discussed. [Preview Abstract] |
Wednesday, March 18, 2009 8:12AM - 8:24AM |
P26.00002: The Image Potential for Graphene with an electrostatic Grating Godfrey Gumbs, Danhong Huang, Pedro Echenique We calculate the surface response function and the image potential of a layered structure of two-dimensional (2D) electron systems (ES). A point charge is placed at a distance away from the surface which is in the $xy$-plane. These 2D layers are coupled through the Coulomb interaction and {\em there is no interlayer electron hopping\/}. The separation between adjacent layers can be adjusted to investigate the role which layer separation and the number of layers play on both the surface response function and the image potential. Specifically, we consider the system composed of graphene layers or the layered 2D electron gas (EG) formed at the interface of a semiconductor heterostructure such as GaAs/AlGaAs. We show that the image potential for graphene is qualitatively the same as for the 2DEG. We examine the way in which the image potential is modified by applying a one-dimensional periodic electrostatic potential (through a gated grating for modulation). These results indicate that the charge screening for graphene is not much different from the 2DEG. [Preview Abstract] |
Wednesday, March 18, 2009 8:24AM - 8:36AM |
P26.00003: Adsorption of Ammonia on Graphene Prasoon Joshi, Hugo Romero, Awnish Gupta, Humberto Gutierrez, Milton Cole, Srinivas Tadigadapa, Peter Eklund We report on experimental studies of NH$_{3}$ adsorption/desorption kinetics on graphene surfaces. The study employs bottom-gated graphene field effect transistors (FETs) supported on Si/SiO$_{2}$ substrates. Detection of NH$_{3}$ occurs through the shift of the source-drain resistance maximum (``Dirac peak'') with gate voltage. The observed shift of the Dirac peak toward negative gate voltages in response to NH$_{3}$ exposure is attributed to the charge transfer from adsorbed NH$_{3}$, with the amount of charge estimated to be $\sim $ 0.06 electrons per molecule. The desorption kinetics of our FET devices is well described by the sum of two exponential terms corresponding to a fast and a much slower process, whose time constants differ by a factor of $\sim $ 9. The two-time constant desorption kinetics is consistent with Fickian-type diffusion of NH$_{3}$ from the interstitial pockets formed at the interface between the graphene and the supporting SiO$_{2}$ gate dielectric. [Preview Abstract] |
Wednesday, March 18, 2009 8:36AM - 8:48AM |
P26.00004: Resist-free method for contacting graphene and few-layer graphene Caterina Soldano, Ather Mahmood, Jeremie Grisolia, Veronica Savu, Juergen Brugger, Erik Dujardin In recent years, discovery of graphene has offered the scientific community an important tool to investigate a variety of fundamental phenomena. Exceptional electronic transport render graphene a promising candidate for future high-performance electronic devices. Conventional techniques to fabricate graphene devices include lithographic approaches, which tend to alter the structure and surface of graphene, and therefore its properties. A graphene contacting method free of any surface damaging and/or modification is indeed in need. Here, we present a simple resist-free non-invasive approach for contacting graphene and/or few-layers graphene. SiN membrane were custum-made and used to mask samples, previously deposited on substrate. Then, evaporation of metal allows to fabricate electrical leads for testing. Further, we present preliminary measurements of the electronic properties (room- and low-temperatures) of one of our typical sample contacted by such technique. [Preview Abstract] |
Wednesday, March 18, 2009 8:48AM - 9:00AM |
P26.00005: Transport studies of highly oriented pyrolytic graphite Aruna N. Ramanayaka, Bhaskar Kaviraj, Ramesh G. Mani Highly Oriented Pyrolytic Graphite (HOPG) consists of stacked sheets of single layers of carbon with weak interlayer interactions, which gives rise to anisotropic transport with striking differences between in-plane and perpendicular transport. Transport studies of single layers of carbon, known as Graphene, have shown striking new features in two dimensional transport, arising from the linear dispersion relation and analogies to quantum electrodynamics. A question of interest for our experiments is to examine the crossover from Graphite to Graphene and trace the three-dimensional to two-dimensional evolution in the transport properties of the layered carbon system. Hence, we report here on our efforts to fabricate specimens starting from commercially available HOPG, and present measurements in magnetic fields upto 12 Tesla, down to 1.5 K. [Preview Abstract] |
Wednesday, March 18, 2009 9:00AM - 9:12AM |
P26.00006: ABSTRACT WITHDRAWN |
Wednesday, March 18, 2009 9:12AM - 9:24AM |
P26.00007: Semiclassical model for the magnetoresistance and Hall coefficient of inhomogeneous graphene Rakesh Tiwari, David Stroud We show that when bulk graphene breaks into n-type and p-type puddles, the in-plane resistivity becomes strongly field dependent in the presence of a perpendicular magnetic field, even if homogeneous graphene has a field-independent resistivity. We calculate the longitudinal resistivity $\rho_{xx}$ and Hall resistivity $\rho_{xy}$ as a function of field for such a system, using the effective-medium approximation. The conductivity tensors of the individual puddles are calculated using a standard Boltzmann approach suitable for the band structure of graphene near the Dirac points. The resulting resistivity saturates, provided that the area fractions $f_n$ and $1 - f_n$ of n and p type puddles are slightly unequal, and agrees with experiments if the relaxation time is weakly field-dependent. The Hall resistivity $\rho_{xy}$ found to change sign at $f_n = 1/2$. [Preview Abstract] |
Wednesday, March 18, 2009 9:24AM - 9:36AM |
P26.00008: Anomalous Quantum Oscillations in Graphene Hybrid Structures Conor Puls, Neal Staley, Ying Liu It is well recognized that the edge states of graphene are interesting and important for both fundamental inquiry and potential practical applications of graphene. However, states associated with a step found in a continuous sheet of graphene with two different thicknesses have not been explored to date. We report a study of graphene hybrid structures featuring such a step. In a bulk hybrid featuring two large-area one- and two-layer graphene, two sets of Landau levels and features related to the interface were found. In edge hybrids featuring a large two-layer graphene with narrow one-layer graphene edges, we observed an anomalous suppression in quantum oscillation amplitude due to the locking of one- and two-layer graphene Fermi energies by charge transfer across the interface. These findings demonstrate the existence of unique interface states and related phenomena deserving of further studies. We will also report relevant studies on epitaxially-grown graphene films. [Preview Abstract] |
Wednesday, March 18, 2009 9:36AM - 9:48AM |
P26.00009: Graphene mediated exchange bias Yuriy Semenov, John Zavada, Ki Wook Kim We have theoretically investigated the role of graphene in mediating the indirect exchange interaction when it is placed between two ferromagnetic dielectric materials. The calculation based on a tight-binding model illustrates that the magnetic interactions at the interfaces affect not only the graphene band structure but also the thermodynamic potential of the system. This induces an indirect exchange interaction between the magnetic layers that can be considered in term of an effective exchange bias field. The analysis clearly indicates a strong dependence of the effective exchange bias on the properties of the mediating layer. Through the dependence on the graphene electro-chemical potential, the effective exchange bias can be modulated electrically over a wide range even at room temperature. This dependence also results in qualitatively different characteristics for the cases involving monolayer and bilayer graphene. The numerical estimation indicates the potential significance of the proposed phenomenon in practical applications. [Preview Abstract] |
Wednesday, March 18, 2009 9:48AM - 10:00AM |
P26.00010: Conductivity engineering of graphene by defect formation Biplab Sanyal Graphene exhibits exotic electronic properties revealed in transport measurements. The possibility to influence the electronic structure and hence control the conductivity by physisorption or doping with adatoms is crucial in view of electronics applications. Here we show that in contrast to expectation, the conductivity of graphene increases with increasing concentration of vacancy defects, with an amount of over one order of magnitude. We obtain a pronounced enhancement of the conductivity after insertion of defects by ab-initio electronic structure calculations. The theoretical results are supported by the experimental studies on carbon nano-sheets. Our finding is attributed to defect induced mid-gap states, which create a region exhibiting metallic behavior around the vacancy defects. The modification of the conductivity of graphene by implementation of stable defects is crucial for the creation of electronic junctions in graphene-based electronics. [Preview Abstract] |
Wednesday, March 18, 2009 10:00AM - 10:12AM |
P26.00011: A computational study of electrical transport in graphene-based films and composites Jeremy Hicks, Ashkan Behnam, Ant Ural We study the electrical behavior of films and composites composed of a mesh of graphene sheets using Monte Carlo simulations. We take into account the sheet-sheet junctions with different areas as well individual graphene sheets in calculating the film/composite transport properties. We find that the resistivity of composites varies by many more orders of magnitude than films approaching the percolation threshold due to tunneling-percolation through the sheet network, but otherwise the two exhibit many of the same scaling trends. Furthermore, we find that resistivity in both cases is a strong function of graphene sheet aspect ratio, density, volume fraction, and device dimensions. We extract important parameters such as the critical exponents near the percolation threshold and compare them with the available experimental data. These results, explained through physical and geometrical arguments, give valuable insights into the factors influencing the electrical transport in graphene sheet films and nanocomposites. Such graphene-based nanomaterials might find applications in many fields such as photovoltaics, sensors, and multifunctional nanocomposites. [Preview Abstract] |
Wednesday, March 18, 2009 10:12AM - 10:24AM |
P26.00012: Investigating the quantum behavior of a graphene-based Josephson Junction Joseph Lambert, Zechariah Thrailkill, Roberto Ramos Recent experiments have demonstrated the Josephson effect in superconducting mesoscopic graphene devices consisting of two superconducting leads separated by a few hundred nanometers, contacted by single and multiple layers of graphene [1]. We report on the progress of low temperature experiments that study the temperature dependence of switching currents in this device. The motivation is to explore the presence of macroscopic quantum metastable states similar to those found in current-biased Josephson junctions. These states are interesting and have been used as basis states for superconducting qubits. [1] H.B. Heersche, P.D. Jarillo-Herrero, J.B. Oostinga, L.M.K. Vandersypen, and A.F.Morpurgo, Induced superconductivity in grapheme, Solid state communications, 143(1-2), 72-76 (2007) [Preview Abstract] |
Wednesday, March 18, 2009 10:24AM - 10:36AM |
P26.00013: Study on the Electronic Band Structures of Doped Graphene C.G. Hwang, Kevin T. Chan, D. Siegel, A.V. Fedorov, Marvin L. Cohen, J.B. Neaton, A. Lanzara Graphene, a carbon sheet self-assembled on a SiC substrate, has been found to undergo changes in an electronic property as a function of doping concentration. Depending on the species of dopants, charge carrier density is gradually modified with increasing dopant coverage. By using angle resolved photoemission spectroscopy, we study how the graphene pi bands are modified by changing doping concentration and we discuss the effect of doping on many-body interaction such as electron-phonon coupling. These results provide new information on the role of electron-phonon coupling for superconductivity in the graphite intercalated compounds. [Preview Abstract] |
Wednesday, March 18, 2009 10:36AM - 10:48AM |
P26.00014: Anomalous thermoelectric transport of Dirac particles in graphene Peng Wei, Wenzhong Bao, Yong Pu, Chun Ning (Jeanie) Lau, Jing Shi We report a thermoelectric transport property study of single layer graphene devices in both classical and quantum Hall regimes. In zero magnetic field, by sweeping the gate voltage V$_{g}$ to vary the carrier density $n_{2D} $, we demonstrate a diverging behavior in the Seebeck coefficient $S_{xx}$, i.e.$S_{xx} \sim 1/\sqrt {n_{2D} } $, which is a direct consequence of the linear energy dispersion of the massless particles. At low temperatures and high carrier densities, the Seebeck coefficient depends linearly on temperature, indicating the validity of the Mott relation. In the applied magnetic fields, we observe an anomalously large Nernst signal($\sim $ 6 $\mu $V/K*T) at the Dirac point. This is another unusual property expected for massless particles. At low temperatures where the quantum Hall effect is observed, both the Seebeck and Nernst signals show oscillations corresponding to the Landau levels manifested in the quantum Hall plateaus. [Preview Abstract] |
Wednesday, March 18, 2009 10:48AM - 11:00AM |
P26.00015: Structure, Stability, Edge States and Aromaticity of Graphene Ribbons Tobias Wassmann, Ari Paavo Seitsonen, A. Marco Saitta, Michele Lazzeri, France Mauri We determine the stability, the geometric, the electronic and magnetic structure of hydrogen-terminated graphene-nanoribbons edges as a function of the hydrogen content of the environment by means of density functional theory [1]. Antiferromagnetic zigzag ribbons are stable only at extremely-low ultra-vacuum pressures. Under more standard conditions, the most stable structures are the mono- and di-hydrogenated armchair edges and a zigzag edge reconstruction with one di- and two mono-hydrogenated sites. At high hydrogen-concentration ``bulk'' graphene is not stable and spontaneously breaks to form ribbons, in analogy to the spontaneous breaking of graphene into small-width nanoribbons observed experimentally in solution [2]. The stability and the existence of exotic edge electronic-states and/or magnetism is rationalized in terms of simple concepts from organic chemistry (Clar's rule). [1] T. Wassmann, et al. Phys. Rev. Lett. 101, 096402 (2008). [2] X. Li et al., Science 319, 1229 (2008); X. Wang et al., Phys. Rev. Lett. 100, 206803 (2008). [Preview Abstract] |
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