Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session U5: Graphene: Transport and Optical Phenomena: Mesoscopics and Harmonic Generation |
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Sponsoring Units: DCMP Chair: Chris Stanton, University of Florida Room: 301 |
Thursday, March 21, 2013 11:15AM - 11:27AM |
U5.00001: Resonant inelastic transmission through a time-modulated region in graphene Li Chang, T. L. Liu, C. S. Chu We investigate a number of resonant transmission processes through a time-modulated-potential region in graphene. Incident energies covering both low and high energy regimes are included, and the time-dependent transmission is treated within a tight-binding model. Three main results are obtained. Dip structures in the transmission are obtained when a band edge is involved. It can occur in the low energy regime, if the graphene is gapped, or in the high energy regime, when a graphene band edge is in the energy neighborhood. These dip structures cause significant deviation from Klein-type perfect transmission. Non-typical Fabry-P\'{e}rot interference is observed when, staying upon a dip structure condition, the transmission exhibits an oscillation that has a longer than expected period in $L$, the width of the time-modulated region. Central band refocusing is found in the low energy regime, where the dominance in the transmission by the central-band will occur periodically with $L$. In all these results, we have demonstrated and analyzed detail intricate resonant interplays between sideband processes. [Preview Abstract] |
Thursday, March 21, 2013 11:27AM - 11:39AM |
U5.00002: Charge transport across tunable superlattice barriers in graphene Sudipta Dubey, Ajay Bhat, Vibhor Singh, Pritesh Parikh, Tanuj Prakash, Abhilash Sebastian, Padmalekha K.G., Krishnendu Sengupta, Vikram Tripathi, Rajdeep Sensarma, Mandar Deshmukh We create an artificial superlattice structure in graphene using an array of top gate and a bottom gate. A superlattice potential modifies the band structure of graphene, so that extra Dirac points appear in the dispersion periodically as a function of the superlattice barrier height. Tuning the amplitude of the barrier thus gives us control over number of Dirac points generated. We have performed measurements on this superlattice structure. Oscillations in resistance are observed when the charge carrier induced by top gate and back gate are of opposite sign. In this region, the number of oscillations increases with increasing gate voltage. Measurements as a function of temperature show that these oscillations persist even at 70 K. The behaviour of these oscillations in presence of magnetic field is also observed. At low magnetic field we see weak localisation behaviour. At high magnetic field, the superlattice is a small perturbation and quantum Hall effect of pristine graphene is restored. [Preview Abstract] |
Thursday, March 21, 2013 11:39AM - 11:51AM |
U5.00003: Graphene under spatially varying external potentials: Landau levels, magnetotransport, and topological modes Si Wu, Matthew Killi, Arun Paramekanti Superlattices (SLs) in monolayer and bilayer graphene, formed by spatially periodic potential variations, lead to a modified bandstructure with extra finite-energy and zero-energy Dirac fermions with tunable anisotropic velocities. We theoretically show that transport in a weak perpendicular (orbital) magnetic field allows one to not only probe the number of emergent Dirac points but also yields further information about their dispersion. or monolayer graphene, we find that a moderate magnetic field can lead to a strong reversal of the transport anisotropy imposed by the SL potential, an effect which arises due to the SL induced dispersion of the zero energy Landau levels. This effect may find useful applications in switching or other devices. For bilayer graphene, we discuss the structure of Landau level wave functions and local density of states in the presence of a uniform bias, as well as in the presence of a kink in the bias which leads to topologically bound `edge states'. We consider implications of these results for scanning tunneling spectroscopy measurements, valley filtering, and impurity induced breakdown of the quantum Hall effect in bilayer graphene. [Preview Abstract] |
Thursday, March 21, 2013 11:51AM - 12:03PM |
U5.00004: Confinement, transport gap, and valley polarization from a double barrier structure in graphene Daniel Gunlycke, Carter White Engineering a gap in graphene without degrading its exceptional transport properties is arguably the main obstacle preventing a breakthrough in graphene-based nanoelectronics. To create such a gap, a lot of effort has been devoted to making graphene nanoribbons. Unlike ordinary nanoribbons, we propose a structure formed between two thin parallel transport barriers that is penetrable by electrons in surrounding graphene states. The transport across this railroad track structure is governed by resonant tunneling through quasi-bound states within the confinement. The transport barriers, modeled by chemically decorated line defects, are highly reflective, causing the resonances to form continuous bands closely matching the band structure of a zigzag ribbon. Because boundary-localized states cannot carry any transport, the resonance bands must terminate at the dimensional crossover between extended and boundary-localized states. As the confined region contains no states near the Fermi level extending across the railroad track structure, electrons approaching it experience a transport gap $E_g=2\hbar v_F/W$, where $W$ is the separation between the barriers. In addition to offering confinement and a transport gap, the structure allows for nearly perfect valley polarization. [Preview Abstract] |
Thursday, March 21, 2013 12:03PM - 12:15PM |
U5.00005: ABSTRACT WITHDRAWN |
Thursday, March 21, 2013 12:15PM - 12:27PM |
U5.00006: Transport Spectroscopy of gate controlled cavity in CVD bilayer graphene transistor Kyunghoon Lee, Yun Suk Eo, Cagliyan Kurdak, Zhaohui Zhong Graphene nanostructure provides an ideal platform for understanding distinctive quantum transport properties such as Klein tunneling and suppression of backscattering due to its chiral nature. Quantum interference of phase coherent electron waves in single-layer graphene has attracted wide attention recently, while few experimental works examine the quantum transport of massive Dirac Fermion in bilayer graphene. To this end, we report the low temperature electrical transport spectroscopy of gate controlled cavity in CVD bilayer graphene transistor. Fabry-Perot like conductance oscillation was observed in both monopolar and bipolar bilayer graphene structures defined by electrostatic gating. Transport comparison between single-layer graphene and bilayer graphene will be also discussed. [Preview Abstract] |
Thursday, March 21, 2013 12:27PM - 12:39PM |
U5.00007: Tunable superconductivity in decorated graphene Zheng Han, Adrien Allain, Laetitia Marty, Nedjma Bendiab, Pierre Toulemonde, Pierre Strobel, Johann Coraux, Vincent Bouchiat Graphene offers an exposed bidimensional gas of high mobility charge carriers with gate tunable density. Its chemical inertness offers an outstanding platform to explore exotic 2D superconductivity. Superconductivity can be induced in graphene by means of proximity effect (by depositing a set of superconducting metal clusters such as lead [1] or tin nanoparticles). The influence of decoration material, density or particles and disorder of graphene will be discussed. In the case of disordered graphene, Tin decoration leads to a gate-tunable superconducting-to-insulator quantum phase transition [2]. Superconductivity in graphene is also expected to occur under strong charge doping [3] (induced either by gating or under chemical decoration [4], in analogy with graphite intercalated compounds). I will also show preliminary results showing the influence of Calcium intercalation of few layer graphene and progress toward the demonstration of intrinsic superconductivity in such systems. [1] B. Kessler et al, Phys. Rev. Lett., \textbf{104}, 047001 (2010). [2] A. Allain et al, Nature Materials, \textbf{11 }, 590 (2012). [3] B. Uchoa and A. H. Castro Neto. Phys. Rev. Lett., \textbf{98}, 146801 (2007). [4] G. Profeta, et al., Nature Physics \textbf{8}, 131 (2012). [Preview Abstract] |
Thursday, March 21, 2013 12:39PM - 12:51PM |
U5.00008: Electronic transport experiments on adatom-decorated graphene E.A. Henriksen, J.P. Eisenstein Single-layer graphene is expected to exhibit a wide range of novel behaviors when decorated with a disperse coating of various adatom species. Toward conducting experiments on these systems, we are developing a cryogenic ultra-high vacuum probe with the capability to explore the electronic transport of graphene and other materials that have been cleaned and annealed {\it in situ}, followed by coating via the controlled deposition of sub-monolayer coverages of a range of elements. We will report our progress on the fabrication of such thin layers, and on the characterization of surface-modified graphene devices. This work is supported by the DOE under grant No. DE-FG03-99ER45766 and the Gordon and Betty Moore Foundation. [Preview Abstract] |
Thursday, March 21, 2013 12:51PM - 1:03PM |
U5.00009: Quantum interference noise near the Dirac point in graphene Nina Markovic, Atikur Rahman, Janice Wynn Guikema We have studied low-frequency noise characteristics in single layer graphene, focusing specifically on the low-carrier density regime. We show that the 1/f noise at low temperatures is dominated by the time-dependent conductance fluctuations which occur due to quantum interference effects. Close to the Dirac point, the noise is reduced in magnetic field, but the relative noise reduction is larger than what might be expected based on the current theoretical understanding of quantum transport in graphene. The results reflect the inherent symmetry of the system and suggest the importance of additional degrees of freedom. [Preview Abstract] |
Thursday, March 21, 2013 1:03PM - 1:15PM |
U5.00010: Noise properties of graphene like systems Avinash Rustagi, C.J. Stanton The unusual electronic properties of graphene and its potential for applications in nanoscale devices motivated us to study the noise properties of materials that have a graphene-like electronic dispersion. For high values of electric field, we find interesting behavior in the noise properties which appear due to hot electron effects. We study the low-frequency noise based on the Boltzmann-Green function method within the relaxation time approximation considering an inelastic scattering term coming from phonon scattering and an elastic scattering term coming from impurity scattering. The steady-state distribution function is evaluated to calculate the average behavior of physical observables like current and energy. We find that as the field strength is increased, the noise \textit{decreases} from the thermal noise value. We have also studied these properties for electronic dispersion with a gap parameter introduced in the Dirac spectrum. The inclusion of gap in the electronic dispersion causes initial heating of the electrons resulting in an increase in noise for intermediate values of field before it decreases at high fields. [Preview Abstract] |
Thursday, March 21, 2013 1:15PM - 1:27PM |
U5.00011: Third harmonic generation in graphene Nardeep Kumar, Jatinder Kumar, Chris Gerstenkorn, Rui Wang, Hsin-Ying Chiu, Arthur Smirl, Hui Zhao We report the measurement of optical third harmonic generation from single-layer graphene and few-layer graphite flakes produced by exfoliation. In the measurements, femtosecond near-infrared laser pulses were used to irradiate the samples. The emission observed scales with the cube of the intensity of the incident near-infrared pulse and with one third of the incident wavelength - both are clear evidences of third harmonic generation. We deduced an effective third-order susceptibility for single layer graphene to be on the order of 10$^{-16}$ m$^2$/V$^2$. By measuring a set of flakes with different numbers of atomic layers, we found that for a few layers, the emission scales with the square of the number of atomic layers. [Preview Abstract] |
Thursday, March 21, 2013 1:27PM - 1:39PM |
U5.00012: Second Harmonic Generation in a Graphe Armchair Nanoribbon Godfrey Gumbs, Yonatan Abranyos The second order nonlinear optical susceptibility $\chi^{(2)}$ for second harmonic generation is calculated for the 11H transition of a graded double quantum well (DQW) structure of undoped-$GaAs/Al_{x}Ga_{1-x}As$. These results are compared with the single quantum well (QW). Our results show that the values of $\chi^{(2)}$ have optimal magnitudes dependent on the width, depth and separation between the QWs in a DQW structure. When the electric field increases, the dipole moment increases due to the increasing separation between the electron and hole wave functions. On the other hand, the oscillator strength of the 11H transition is reduced as a result of the decrease in the overlap of the electron and hole envelope functions. These two competing factors give rise to optimal conditions for the enhancement of the second order nonlinear susceptibility $\chi^{(2)}$. It is demonstrated that $\chi^{(2)}$ for the DQW structure is more enhanced than for the biased single QW. [Preview Abstract] |
Thursday, March 21, 2013 1:39PM - 1:51PM |
U5.00013: Optical Third-Harmonic Microscopy of Graphene Jerry I. Dadap, Sung-Young Hong, Nicholas W. Petrone, Po-Chun Yeh, James C. Hone, Richard M. Osgood, Jr We report strong third-harmonic (TH) generation in monolayer graphene mounted on an amorphous silica substrate using a photon energy that is three-photon resonant with the exciton-shifted van Hove singularity at the M-point of graphene. Our polarization-dependent and azimuthal rotation measurements confirm the expected isotropic symmetry properties for the TH nonlinear optical process in graphene. Since this monolayer graphene TH signal exceeds that of bulk glass by more than two orders of magnitude, the signal contrast permits background-free scanning of graphene and provides structural information that is difficult to obtain via linear optical microscopy. We also discuss the dependence of TH signals on the number of graphene layers and compare the graphene signal strength with that from crystalline Au(111) sample. [Preview Abstract] |
Thursday, March 21, 2013 1:51PM - 2:03PM |
U5.00014: Tunable THz Metamaterial Coupled to Graphene Tsung-Ta Tang, Sufei Shi, Long Ju, Feng Wang Metamaterial is a periodic sub-wavelength dielectric structure which can be tailored to have a strong resonance at particular frequencies. However, changing the electromagnetic response of metamaterial often involves changing the design. On the other hand, graphene is an atomic layer of carbon atoms arranged in honeycomb structure and its conductivity in THz regime is highly tunable by changing the Fermi energy of graphene. In our study, we couple graphene to a THz metamaterial device efficiently and demonstrate that the resonance of THz metamaterial can be changed over a wide range by controlling the conductivity of graphene. This graphene-THz metamaterial hybrid device can be used for future THz application such as THz modulator, which can be controlled electrostatically. [Preview Abstract] |
Thursday, March 21, 2013 2:03PM - 2:15PM |
U5.00015: Tunable plasmonic resonators in Graphene with extreme light confinement Victor Brar, Min Seok Jang, Josue Lopez, Harry Atwater Graphene plasmons can display a number of interesting properties including small mode volumes, long lifetimes and energies that vary with the sheet charge density. In this work we investigate both experimentally and theoretically the behavior of graphene plasmons in the Mid-IR regime. We find that graphene monolayers that have been patterned with features from 30-100nm can support gate-tunable resonances across the Mid-IR, from 10-5um with charge densities up to 10$^{12}$ e/cm$^{2}$. In our extreme limit, we observe that 30nm sized features cut in graphene can support plasmon resonances for light at 6um wavelengths, indicating mode volumes that are $\sim$ 10$^{6}$ smaller than free space. We further show that these graphene plasmons can couple to phonon polaritons in the supporting dielectric substrate to create multiple new resonances at wavelengths near 10um. These results are analyzed in terms of both analytical calculations and finite element models. [Preview Abstract] |
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