Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session J21: Focus Session: Graphene: Transport I |
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Sponsoring Units: DMP Chair: Millie Dresselhaus, Massachusetts Institute of Technology Room: Portland Ballroom 251 |
Tuesday, March 16, 2010 11:15AM - 11:27AM |
J21.00001: Impact of coulomb impurities on transport properties of graphene nanoribbons Christian Smith, Masahiro Ishigami Coulomb impurities create charge puddles in graphene sheets, which dominate transport properties. We measured transport properties of graphene nanoribbons while varying charged impurity density in ultra high vacuum to directly probe the effect of the dimensional confinement. We will discuss our results in light of recent predictions [1] that dimensional crossover will occur as the ribbon width becomes on the order of the impurity-induced puddles. \\[4pt] [1] S. Adam et al., Phys. Rev. Lett. 101, 046404 (2008) [Preview Abstract] |
Tuesday, March 16, 2010 11:27AM - 11:39AM |
J21.00002: Carrier scattering, mobilities and electrostatic potential in mono-, bi- and tri-layer graphenes Wenjuan Zhu, Vasili Perebeinos, Marcus Freitag, Phaedon Avouris The carrier density and temperature dependence of the Hall mobility in mono-, bi- and tri-layer graphene has been systematically studied. We found that as the carrier density increases, the mobility decreases for mono-layer graphene, while it increases for bi-layer/tri-layer graphene. This can be explained by the different density of states in mono-layer and bi-layer/tri-layer graphenes. In mono-layer, the mobility also decreases with increasing temperature primarily due to substrate surface polar phonon scattering. In bi-layer/tri-layer graphene, on the other hand, the mobility increases with temperature because the electric field of the substrate surface polar phonons is effectively screened by the additional graphene layer(s) and the mobility is dominated by Coulomb scattering. We also find that the temperature dependence of the Hall coefficient in mono-, bi- and tri-layer graphene can be explained by the formation of electron and hole puddles in graphene. This model also explains the temperature dependence of the minimum conductance of mono-, bi- and tri-layer graphene. The electrostatic potential variations across the different graphene samples are extracted. [Preview Abstract] |
Tuesday, March 16, 2010 11:39AM - 11:51AM |
J21.00003: Quantum Oscillations in Microwave Conductance of Graphene Pei-hsun Jiang, Andrea Young, Philip Kim, Lloyd W. Engel, Daniel C. Tsui We report measurements of the microwave-frequency, low-temperature conductance of mechanically-exfoliated graphene on SiO$_2$/Si. The two-terminal microwave conductance ($G$) of a graphene flake is calculated from signals transmitted through a planar metal film pattern which resides on the SiO$_2$ surface and connects to the graphene. At high magnetic field, we observe quantum oscillations of $G$ vs the magnetic field and the graphene carrier density. We find $G$ to be independent of the frequency ($f$) from DC up to 8.5 GHz. This result is consistent with the low $f$ limit, $2\pi f\tau<<1$, where $\tau$ is the scattering time. [Preview Abstract] |
Tuesday, March 16, 2010 11:51AM - 12:27PM |
J21.00004: Graphene Update Invited Speaker: I will overview the latest progress of our group in Manchester. This will cover such subjects as intrinsic magnetism in graphene, better understanding of its scattering mechanisms, electron transport in suspended devices with mobilities $>$1,000,000 $cm^2$/Vs (including the fractional quantum Hall effect in single and double layer graphene) and properties of graphene's chemical derivatives such as graphane. \\[4pt] For reviews on graphene, see A. K. Geim, K. S. Novoselov. \textit {Nature Mater.} \textbf{6}, 183 (2007). A. K. Geim, \textit{Science} \textbf{324}, 1530 (2009). A. H. Castro Neto \textit{et al}, \textit{Rev. Mod. Phys.} \textbf{81}, 109 (2009). [Preview Abstract] |
Tuesday, March 16, 2010 12:27PM - 12:39PM |
J21.00005: Impurity Induced Spin-Orbit Coupling in Graphene Antonio Castro Neto, Francisco Guinea We study the effect of impurities in inducing spin-orbit coupling in graphene. We show that the sp3 distortion induced by an impurity can lead to a large increase in the spin-orbit coupling with a value comparable to the one found in diamond and other zinc-blende semiconductors. The spin-flip scattering produced by the impurity leads to spin scattering lengths of the order found in recent experiments. Our results indicate that the spin-orbit coupling can be controlled via the impurity coverage. [Preview Abstract] |
Tuesday, March 16, 2010 12:39PM - 12:51PM |
J21.00006: Insulating Behavior in Graphene with Irradiation-induced Lattice Defects Jian-Hao Chen, Ellen Williams, Michael Fuhrer We irradiated cleaned graphene on silicon dioxide in ultra-high vacuum with low energy inert gas ions to produce lattice defects [1], and investigated in detail the transition from metallic to insulating temperature dependence of the conductivity as a function of defect density. We measured the low field magnetoresistance and temperature-dependent resistivity \textit{in situ} and find that weak localization can only account for a small correction of the resistivity increase with decreasing temperature. We will discuss possible origins of the insulating temperature dependent resistivity in defected graphene in light of our recent experiments. \\[4pt] [1] Jian-Hao Chen, W. G. Cullen, C. Jang, M. S. Fuhrer, E. D. Williams, \textit{PRL} \textbf{102}, 236805 (2009) [Preview Abstract] |
Tuesday, March 16, 2010 12:51PM - 1:03PM |
J21.00007: Transition from Quantum Hall metal (QHM) to localized Hall insulator (LHI) in graphene Liyuan Zhang, Yan Zhang, Maxim Khodas, Emilio Mendez, Tonica Valla, Igor Zaliznyak Graphene provides a new system to study the quantum Hall effect (QHE) of two-dimensional Dirac-like electronic excitations. We had investigated experimentally the magneto-transport in single layer graphene close to the charge neutrality point (CNP). We found that QHE regimes at low carrier density depend markedly on the mobility of graphene devices. In our high mobility samples, we had observed a breakdown of the $N $= 0 Quantum Hall state and the appearance of the insulating behavior at high magnetic field and low temperature. We also obtained an evidence of a well-defined transition from the Quantum Hall metal (QHM) to the localized Hall insulator (LHI) with decreasing filling of the N = 0 Landau level. This is a quantum phase transition, which was already demonstrated in traditional two dimension electron gas system. [Preview Abstract] |
Tuesday, March 16, 2010 1:03PM - 1:15PM |
J21.00008: Can electrons in Graphene be localized?---hint from a numerical study of single and double impurities and disordered systems. Zhou Li, Stepan Grinek, Ming Li, Jie Chen, Frank Marsiglio Different from long range coulomb impurities [1], we found that for single or double on-site attractive impurities in gapped graphene, the bound state in the gap will not enter the lower energy continuum as the strength of the impurity is increased. Instead, the spectral weight of the bound state will decrease to zero before the LDOS peak reaches the lower energy continuum. Moreover, the asymptotic behavior of the electronic wave function for different attractive potentials is quite different. The probability distribution for a quantum well will decay exponentially while for a screened coulomb potential it will decay as 1/r$^{2}$. For disordered systems, first we are interested in studying a type of bond length disorder, which will change the hopping energy in a specific direction in a random way. By examining the wave functions we are able to visualize the localization of the electrons. It is straightforward to examine systems with other kinds of disorder, such as randomly distributed dimers, trimers and so on. Reference: [1] V. M. Pereira et.al, Physical Review B, 78, 8, 2008, pp. 085101 [Preview Abstract] |
Tuesday, March 16, 2010 1:15PM - 1:27PM |
J21.00009: Electron transport in graphene at extremely high carrier doping Dmitri Efetov, Philip Kim Owing to the low dimensionality, carrier doping in graphene can be significantly changed by the electric field effect or the chemical adsorption of gaseous dopands. At extremely high doping levels, where carrier densities reach beyond 10$^{14}$ cm$^{-2}$ the electronic structure at the Fermi level of graphene is expected to be substantially modified, as higher band structure effects such as trigonal warping or Fermi surface renormalization due to electron-phonon coupling take place. In this presentation we will present electron transport of highly doped graphene samples. By employing a poly(ethylene oxide)-LiClO$_{4}$ electrolyte gate we achieve unpreceded carrier densities up to 4x10$^{14}$ cm$^{-2}$ in graphene single and bilayers, attaining a Fermi energy change of $\sim $ 2 eV away from the charge neutrality point. We will present resistivity, as well as Magneto-resistance and Hall measurements in this extreme carrier doping limit. [Preview Abstract] |
Tuesday, March 16, 2010 1:27PM - 1:39PM |
J21.00010: Low frequency noise in graphene Tracy Moore, David Tobias, Liang Li, Vinod Sangwan, Michael Fuhrer, Ellen Williams Low frequency, 1/f noise is a poorly understood, commonly occurring phenomenon that is important for sensor technology. Hooge's empirical law describes 1/f noise in an overwhelming number of materials. We have measured 1/f noise in four probe configuration graphene transistors at temperatures ranging from 4 to 300 K. The power spectral density as a function of frequency is found to vary as a function of temperature and gate voltage. Measured 1/f noise will be discussed in terms of Hooge's law and alternative models. [Preview Abstract] |
Tuesday, March 16, 2010 1:39PM - 1:51PM |
J21.00011: Magneto-transport Properties in Suspended Graphene Devices Suyong Jung, Nikolai Klimov, David Newell, Joseph Stroscio, Nikolai Zhitenev High carrier mobility and long coherence lengths are the main attributes which have attracted so much attention to graphene as a new electronic material. Recent studies have shown that electronic properties of graphene are extremely sensitive to disorder, particularly those induced by substrate interactions. By simply isolating graphene devices from the substrate by suspending them, however, they have shown interesting charge transport behaviors such as ballistic transport [1] and the fractional quantum Hall effects[2,3], which can be attributed to the intrinsic electronic properties of graphene. In this talk, we present results on magneto-transport measurements of suspended graphene devices with different geometries and degrees of disorder as a function of temperature. Two- and four-probe measurements of devices with different aspect ratios are compared and discussed. [1] X. Du et al., Nature Nanotechnology 3, 491 (2008). [2] X. Du et al., Nature 462, 192 (2009). [3] K. Bolotin et al., Nature 462, 196 (2009). [Preview Abstract] |
Tuesday, March 16, 2010 1:51PM - 2:03PM |
J21.00012: Transport Properties of Fluorinated Graphene S.-H. Cheng, X. Hong, J. Zhu We attach fluorine atoms to single-layer graphene sheets through \textit{sp$^{3}$} bonding and study the effect of fluorination on electrical transport. This chemical modification occurs in fluorine-containing gas through the assistance of plasma. Raman spectra of fluorinated graphene show the appearance of the \textit{D} band, whose intensity varies with plasma settings. In lightly fluorinated graphene, the \textit{D} band completely disappears after the sample is thermally reduced in forming gas. This observation suggests that fluorine atoms can be attached and removed from the graphene plane reversibly without creating vacancies. On the other hand, in heavily fluorinated samples, the reduction process no longer restores pristine graphene, suggesting damage to the \textit{sp$^{2}$} carbon network. The temperature-dependent resistivity of fluorinated graphene exhibits insulating behavior, which can be described by variable range hopping in 2D at low carrier densities but deviates from this model at high carrier densities. We discuss the origin of these results. [Preview Abstract] |
Tuesday, March 16, 2010 2:03PM - 2:15PM |
J21.00013: On the graphene minimum conductivity from density functional theory Juan Jose Palacios Fully quantum mechanical estimates of the minimum conductivity for unsuspended graphene are presented here. Ripples and charged impurities are considered as the sole sources of disorder and, contrary to prevailing quantum transport calculations, electron-electron interactions are included and fully accounted for in the framework of density functional theory. Our findings, for the types of disorder considered, are conclusive. (i) The conductivity always increases with respect to the clean limit value and becomes non-universal. (ii) Ripples increase the clean-limit conductivity, but do not suffice to explain the observed range of conductivity values. (iii) Charged impurities also increase the conductivity, but only when placed extremely close to graphene as, for instance, in between the graphene flake and the substrate or on top of it, can account for typical experimental values. (iv) Contrary to prevailing semiclassical theoretical estimates, the conductivity never decreases with impurity concentration for up to the highest imaginable values of this concentration. Finally, (v) our calculations corroborate previous theoretical work, agreeing with experimental findings such as the observed linear behavior of the conductivity with density as well as the observed different mobilities for electrons and holes. [Preview Abstract] |
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