Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session M17: Graphene: Terahertz Physics and Plasmons |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Junichiro Kono, Rice University Room: 102AB |
Wednesday, March 4, 2015 11:15AM - 11:27AM |
M17.00001: Optimizing Broadband Terahertz Modulation with Hybrid Graphene/Metasurface Structures Sufei Shi, Bo Zeng, Hui-Ling Han, Xiaoping Hong, Hsin-Zon Tsai, Hae Sae, Alex Zettl, Mike Crommie, Feng Wang We demonstrate efficient terahertz (THz) modulation by coupling graphene strongly with a broadband THz metasurface device. ~This THz metasurface, made of periodic gold slit arrays, shows near unity broadband transmission that arises from coherent radiation of the enhanced local-field in the slits. Utilizing graphene as an active load with tunable conductivity, we can significantly modify the local-field enhancement and strongly modulate the THz wave transmission. This hybrid device also provides a new platform for possible nonlinear THz spectroscopy study of graphene. [Preview Abstract] |
Wednesday, March 4, 2015 11:27AM - 11:39AM |
M17.00002: Full-range Gate-controlled Terahertz Phase Modulation with Graphene Metasurfaces Qiong Wu, Ziqi Miao, Xin Li, Ding Kun, Qiong He, Zhenhua An, Yuanbo Zhang, Lei Zhou Local phase control of electromagnetic wave is the basis of a diverse set of applications such as hologram imaging, polarization manipulations and wave-front controls. Here, we demonstrate full-range THz phase modulation realized on a metasurface featuring magnetic resonators that are coupled with graphene as a tunable loss. A gate bias applied through ion liquid tunes graphene's optical conductivity, turns the coupled system from an under-damped resonator to an over-damped one, and induces dramatic modulation in the phase of the reflected wave. Our one-port resonator (i.e. resonator with only reflection channel) model reveals the underlying mechanism of our extreme phase modulation, and points to general guidelines for achieving large, tunable phase modulation in THz regime. A gate-tunable polarizer will be presented as an early demonstration of the capability of our graphene metasurfaces. [Preview Abstract] |
Wednesday, March 4, 2015 11:39AM - 11:51AM |
M17.00003: Coupling of strongly localized graphene plasmons to molecular vibrations Damon Farmer, Yilei Li, Hugen Yan, Xiang Meng, Wenjuan Zhu, Richard Osgood, Tony Heinz, Phaedon Avouris In this paper, we first present a determination of the out-of-plane confinement of the plasmons in graphene nanoribbons. Using light with a free-space wavelength of $ \sim 6 \mu$m, we excite plasmons in graphene nanoribbons that are $\sim 100$ nm wide. A red-shift in the plasmon frequency is induced by a thin layer of Poly (methyl methacrylate) (PMMA) adsorbed onto the nanoribbons surface due to dielectric screening effect. With increasing thickness of the PMMA layer, we observe a saturation of the frequency shift, from which we deduce an out-of-plane field plasmon field decay length of $\sim 10$ nm. The strongly confined plasmons in graphene produce significant enhancement of the field intensity. We show that this enhancement strengthens the coupling of graphene plasmon to vibrations in the PMMA molecules. The enhanced interaction is manifested through induced transparency in the graphene plasmon optical response when the plasmon and the vibrational frequencies are matched. We also show that this coupling is of an electromagnetic nature by comparing the evolution of the line shape as a function of the detuning of the two frequencies to simulations using the finite-difference time-domain method. [Preview Abstract] |
Wednesday, March 4, 2015 11:51AM - 12:03PM |
M17.00004: Effects of screening on the propagation of graphene surface plasmons Ken-ichi Sasaki, Norio Kumada We investigated surface plasmons in epitaxial graphene, while paying particular attention to the effect of interface states and resistivity on the transport properties[1,2]. The propagation velocity of the surface plasmons is much slower than the electron Fermi velocity when the screening effect provided by interface states is taken into account. Furthermore, slow-moving surface plasmons undergo a strong diffusion when the Fermi energy is near the Dirac point. This is shown by a numerical simulation of an RLC circuit model and its continuum approximation known as the telegrapher's equation. We could explain recent experimental results for the surface plasmons satisfactorily. [1] Kumada {\it et al.}, New J. Phys. {\bf 16}, 063055 (2014). [2] Sasaki and Kumada, Phys. Rev. B {\bf 90}, 035449 (2014). [Preview Abstract] |
Wednesday, March 4, 2015 12:03PM - 12:15PM |
M17.00005: Retardation effect in graphene plasmonics Hugen Yan Localized plasmons in graphene micro- and nano-structures have attracted lots of attention recently. Typically the size of the graphene structure is much smaller than the on-resonance light wavelength and the quasi-electrostatic treatment of the light-matter interaction is sufficient. However, with increasing graphene structure size and stacked layer thickness, the quasi-electrostatic treatment fails. Retardation effect and dynamic depolarization have to be taken into account. In the paper, we'll focus on two major topics related to the retardation effect. First, ultralow damping of graphene plasmons can be achieved in ultra-large graphene disk and ribbon arrays. Second, the coupling of graphene structures in the same array is radiative in nature and the resonance associated with the periodic lattice of the graphene disk or ribbon arrays play an role in the plasmonic response. [Preview Abstract] |
Wednesday, March 4, 2015 12:15PM - 12:27PM |
M17.00006: Plasmon-enhanced terahertz photodetection in graphene Xinghan Cai, Andrei Sushkov, Mohammad Jadidi, R.L. Myers-Ward, A.K. Boyd, K.M. Daniels, D. Kurt Gaskill, Thomas Murphy, H. Dennis Drew, Michael Fuhrer Graphene is a promising material for high speed room-temperature terahertz photodetection. However, the limited absorption in monolayer graphene remains a key challenge. We present here a large area terahertz detector that utilizes a plasmonic resonance in sub-wavelength graphene micro-ribbons to increase the absorption efficiency, and exploits the hot-electron photothermoelectric effect for detection. Through Fourier transform infrared spectroscopy we show that by tailoring the orientation of the graphene ribbons with respect to an array of sub-wavelength bimetallic electrodes, the plasmonic resonance can be efficiently excited, with a gate-tunable resonance frequency in the terahertz range. Polarization-dependent photoresponse measurements show an enhanced photothermal voltage between the outermost electrodes due to the plasmonically enhanced absorption. [Preview Abstract] |
Wednesday, March 4, 2015 12:27PM - 12:39PM |
M17.00007: Controlling Terahertz Waves using Graphene Supercapacitors Nurbek Kakenov, Osman Balci, Emre O. Polat, Hakan Altan, Coskun Kocabas Ability to control density of high mobility charge carriers on graphene provides a unique platform to control electromagnetic waves in a broad spectrum. In this work, we demonstrate a terahertz intensity modulator using a graphene supercapacitor which consists of two large area graphene electrodes and electrolyte medium. This simple device structure enables us to modulate THz waves in a broad spectrum without any metallic gate electrodes. The mutual electrolyte gating between the graphene electrodes provides a very efficient electrostatic doping with Fermi energies of 1 eV. We show that, the graphene supercapacitor yield more than 50{\%} modulation between 0.1 to 1.4 THz with operation voltages less than 3V. The low insertion losses, the simplicity of the device structure and polarization independent device performance are the key attributes of graphene supercapacitors for THz applications. [Preview Abstract] |
Wednesday, March 4, 2015 12:39PM - 12:51PM |
M17.00008: THz pump-THz probe study of electrostatically gated graphene Jingdi Zhang, Mengkun Liu, Martin Wagner, D. N. Basov, Richard D. Averitt We investigate ultrafast carrier dynamics in graphene using THz-pump THz-probe spectroscopy. In contrast to recent studies using optical excitation [1] [2], THz excitation exclusively initiates intra-band transitions, resulting in an increase in the carrier scattering rate. The corresponding transient peak of the transmitted probe signal scales linearly with the E-field of the incident THz pump pulse. Further, the decay time of the excited carriers is independent of the gating voltage. As the Fermi level is tuned toward the charge neutral point (CNP) by varying the electrostatic gate voltage, the induced increase in transmission is strongly suppressed. We believe that the low density of states near the CNP is responsible for this suppression. [1] Shi, S. F., Tang, et. al.~\textit{Nano Lett.},~\textit{14}(3), 1578-1582 (2014). [2] A. J. Frenzel, et. al. \textit{Phys. Rev. Lett. 113, 056602 (2014).} [Preview Abstract] |
Wednesday, March 4, 2015 12:51PM - 1:03PM |
M17.00009: Top Gated Graphene PN junctions for THz detection Anthony Boyd, Anindya Nath, Mehdi Jadidi, Ryan Suess, Andrei Sushkov, Gregory Jenkins, H. Dennis Drew, Thomas Murphy, Rachael Myers-Ward, Kevin Daniels, D. Kurt Gaskill The search for terahertz (THz) detectors based on graphene is encouraged by the fact that the ballistic regime in graphene occurs at room temperature over a distance of few hundred nanometers. The naturally occurring 2-DEG carriers have extremely high intrinsic mobility at room temperature. Despite being only one atomic layer thick, graphene still adsorbs several percent of incoming THz radiation well. THz detectors are fabricated on epitaxial graphene using an improved lithography process using lift off resist to achieve low contact resistance [1]. The devices are field effect transistors constructed with a thin asymmetric nichrome (NiCr) top gate that facilitates tuning the photovoltaic response. The thin NiCr gate possesses a sheet resistance of 390 ohms which enables better matching of free space and does not block the incoming Thz radiation. \\[4pt] [1] Nath Anindya et al Applied Physics Letters 104, 224102 (2014) [Preview Abstract] |
Wednesday, March 4, 2015 1:03PM - 1:15PM |
M17.00010: Strong exciton-plasmon coupling in graphene-semiconductor structures Tigran V. Shahbazyan, Kirill A. Velizhanin We study strong coupling between plasmons in monolayer doped graphene and excitons in narrow gap semiconductor quantum well separated from graphene by a potential barrier. We show that Coulomb interactions between excitons and plasmons result in mixed states described by Hamiltonian similar to one describing exciton-polaritons and derive the exciton-plasmon coupling parameter that depends on system geometry and material properties. We calculate numerically the Rabi splitting of exciton-plasmariton dispersion branches for several semiconductor materials and find that it can reach 100 meV for small graphene and quantum well separations. [Preview Abstract] |
Wednesday, March 4, 2015 1:15PM - 1:27PM |
M17.00011: Plasmons in metal contacted graphene M.M. Jadidi, A.B. Suchkov, R.L. Myers-Ward, A.K. Boyd, K.M. Daniels, D.K. Gaskill, H.D. Drew, T.E. Murphy Subwavelength graphene structures exhibit standing-wave plasmon resonances throughout the terahertz spectral range that can be tuned by application of a gate voltage. These features make graphene an attractive candidate for a variety of electrically tunable terahertz devices, including filters, sensors, sources, and modulators. Plasmonic modes have been observed and analyzed in finite-size graphene elements such as ribbons and disks. However, nearly all optoelectronic applications require electrical connection to the graphene element, which drastically alters the plasmonic boundary conditions and mode structure. We present a study of the effects of conductive electrical contacts on the plasmonic modes of a graphene channel, and examine how the contacts affect the coupling to and from free-space radiation. We show that radiation effects are essential in defining and understanding the properties and linewidths of these modes. We also study how the graphene plasmon mode interacts with the antenna modes of the contacts. These results provide valuable insight for designing antenna-coupled graphene plasmonic devices, including detectors and emitters. [Preview Abstract] |
Wednesday, March 4, 2015 1:27PM - 1:39PM |
M17.00012: Electro-optic and Many-body Effects on Optical Absorption of Twisted Bilayer Graphene Kan-Heng Lee, Lujie Huang, Cheol-Joo Kim, Jiwoong Park In twisted bilayer graphene (tBLG), the interlayer rotation angle between the two graphene layers induces additional angle-dependent van Hove singularities (vHSs) in its band structure where the two Dirac cones from each layer intersect. These vHSs introduce extra angle-dependent absorption peaks in the optical absorption spectra of tBLG. Here, we experimentally investigate the effects of the overall doping and the interlayer potential on these interlayer absorption features at various angles. We independently tune the doping concentration of each layer with a newly-developed, optically transparent, dual-gate transistor geometry to perform simultaneous optical and electrical measurements. Our data show strong electro-optic phenomena in the optical absorption of tBLG: the peak energy and width of the interlayer resonance feature sensitively depends on the overall doping and interlayer potential. We explain our observation using a simple band picture as well as many-body effects. Our study provides a powerful experimental platform for studying more complicated structures such as rotated tri- and multi-layer graphene systems in the future. Moreover, the understanding of electro-optic and many-body effects in these materials opens up a way for novel electrochromic devices. [Preview Abstract] |
Wednesday, March 4, 2015 1:39PM - 1:51PM |
M17.00013: Doping and Field Dependent Electrical Conductivity of Angle-Resolved Twisted Bilayer Graphene Lujie Huang, Cheol-Joo Kim, Adam Wei Tsen, Lola Brown, Jiwoong Park In twisted bilayer graphene (tBLG), the interlayer interaction induces additional van Hove singularities (VHS) and mini-gaps near the intersections between the Dirac cones of the two layers; this results in several electrical and optical phenomena at an energy level that monotonically increases with the twist angle $\theta $. While there exist previous studies on the electrical and optical properties of tBLG, the electrical conductivity of tBLG and its dependence on the overall doping and interlayer potential (field) have not been measured using tBLG samples with known $\theta $. Here, we report the electrical conductivity of $\theta $-resolved tBLG in a dual-gate field effect transistor geometry which allows an independent control of the doping and interlayer potential. In large$\theta $ tBLG, the total conductivity is approximately proportional to the total carrier density (the sum of the carrier number densities from the top and the bottom layers), indicating that large$\theta $ tBLG acts as two independent single layers carrying the electrical current in parallel. Among tBLG samples with a small $\theta $, however, we observe an extra resistance peak besides the Dirac point, which may correspond to the minigap near the VHS. In order to perform further experiments for this small-$\theta $ tBLG samples, we use a doubletransfer of CVD grown graphene films with a uniform lattice orientation over a large scale. This allows a direct optical characterization in the relevant IR wavelengths, a critical capability for determining and the twist angle $\theta $. [Preview Abstract] |
Wednesday, March 4, 2015 1:51PM - 2:03PM |
M17.00014: Resonant Tunneling and Intrinsic Bistability in Twisted Graphene Structures Joaquin Rodriguez-Nieva, Mildred Dresselhaus, Leonid Levitov Bistable systems exhibit several distinct macroscopic states and can switch between them upon variation of some control parameter. Nonvolatile electronic systems that exhibit intrinsic bistability and fast switching times are desirable for low-power memory and logic. Experimental realizations of such systems, however, are scarce. We propose a novel mechanism for intrinsic bistability in van der Waals heterostructures formed by twisted graphene monolayers. Bistability in these systems originates from resonant tunneling and charge coupling between different graphene layers. These characteristics, governed by Dirac-like spectrum and Moir\'{e} periodicity of the tunneling Hamiltonian, allow multiple stable states in the sequential tunneling regime. In the bistability region, an intermediate electrically decoupled graphene layer can, for the same external bias, be either in a resonant or non-resonant state with respect to the top/bottom layer. Features of interest, such as resonant tunneling, negative differential resistance and bistability, are controlled by parameters easily accessible in experiments, namely the twist angle and interlayer conductances. We estimate the power required to retain this state, switching times, and assess volatility of such intrinsically bistable systems. [Preview Abstract] |
Wednesday, March 4, 2015 2:03PM - 2:15PM |
M17.00015: Discovery of bound excitons in twisted bilayer graphene Hiral Patel, Jiwoong Park, Matt Graham Recent first principle Bethe-Salpeter simulations of twisted bilayer graphene (tBLG), predict that the unique geometry of tBLG's overlapping interlayer 2p orbitals produce a strong destructive coherence effect that results in stable, strongly bound exciton states. We directly probe the electronic dynamics of twisted bilayer graphene for the first time by developing a unique ultrafast confocal microscopy approach that combines transient absorption, and transmission electron microscopy. We find resonantly excited twisted bilayer regions display distinct, long-lived dynamics that are not present in 0$^{\mathrm{o}}$ stacked bilayers. We further map out the electronic structure using one and two-photon transient absorption microscopy to observe signatures of both unbound and strongly bound excitonic states predicted by the theory. The probable existence of the stable excitons opens up the possibility of efficient carrier extraction by exploiting the unusual hybrid metallic-excitonic nature in twisted bilayer graphene systems. [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. |
© 2024 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