Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session K31: THz and Ultrafast Measurements in 2D Materials |
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Sponsoring Units: DCMP DMP Chair: Abdel El Fatimy, Georgetown University Room: 294 |
Wednesday, March 15, 2017 8:00AM - 8:12AM |
K31.00001: Magneto-plasmonic terahertz resonances in patterned graphene metasurfaces Jean-Marie Poumirol, Peter Liu, Michele Tamagnone, Tetiana Slipchenko, Luis Martin-Moreno, Juan Mosig, Jerome Faist Faist, Alexey B. Kuzmenko When the time reversal symmetry is broken by a magnetic field, graphene displays strong non-reciprocal magneto-optical effects in the terahertz range such as magnetic circular dichroism and the Faraday rotation. Here we demonstrate that both these effects can be tuned over a large portion of the THz range due to strong magneto-plasmonic resonances that appear in patterned graphene. We studied different patterned types of graphene metasurfaces, such as periodic arrays of anti-dots, squares and metal-ring resonators. Importantly, the frequency and the intensity of the resonances can be efficiently controlled by electrostatic doping. Overall, combining this plasmonic control with magnetic and electronic biasing demonstrated that that non-reciprocity in graphene can be modulated and tuned at frequencies well beyond the cyclotron resonance in unpatterned graphene samples. [Preview Abstract] |
Wednesday, March 15, 2017 8:12AM - 8:24AM |
K31.00002: THz-circuits driven by photo-thermoelectric, gate-tunable graphene-junctions Alexander Holleitner We show that dual-gated graphene junctions can be functional parts of THz-circuits. As the underlying optoelectronic process, we exploit ultrafast photo-thermoelectric currents. We describe an immediate photo-thermoelectric current of the unbiased device following a femtosecond laser excitation. For a picosecond time-scale after the optical excitation, an additional photo-thermoelectric contribution shows up, which exhibits the fingerprint of a spatially inverted temperature profile. The latter can be understood by the different time-constants and thermal coupling mechanisms of the electron and phonon baths within graphene to the substrate and the metal contacts. The interplay of the processes gives rise to ultrafast electromagnetic transients in high-frequency circuits, and it is equally important for a fundamental understanding of graphene-based ultrafast photodetectors and switches. [Preview Abstract] |
Wednesday, March 15, 2017 8:24AM - 8:36AM |
K31.00003: Ultrafast Optical Response of Graphene/$LaAlO_3/SrTiO_3$ Heterostructure Lu Chen, Erin Sutton, Jianan Li, Qing Guo, Mengchen Huang, Jen-Feng Hsu, Brian D'Urso, Jung-Woo Lee, Hyungwoo Lee, Chang-Beom Eom, Patrick Irvin, Jeremy Levy Graphene is a promising tunable plasmonic material in the terahertz regime. Plasmons can be induced in graphene by femtosecond laser excitation, and their resonance frequency can be gate-tuned over a broad terahertz range\footnote{L. Ju, \textit{et al.}, Nature Nanotech. \textbf{6}, 630 (2011)}. Another 2D electron system, the complex-oxide heterostructure LaAlO$_3$/SrTiO$_3$, has been shown to exhibit great promise for control and detection of broadband THz emission at extreme nanoscale dimensions\footnote{Y. Ma, \textit{et al.}, Nano Lett. \textbf{13}, 2884 (2013)}. Recently, we have successfully integrated these two platforms: we have created graphene/LaAlO$_3$/SrTiO$_3$ structures with high mobility in the graphene channel and oxide nanostructures directly underneath the graphene layer. Here we describe new experiments that probe graphene plasmonic behavior using this nanoscale THz spectrometer. This unprecedented control of THz radiation at 10 nm length scales creates a pathway toward hybrid THz functionality in graphene/LaAlO$_3$/SrTiO$_3$ heterostructures. [Preview Abstract] |
Wednesday, March 15, 2017 8:36AM - 8:48AM |
K31.00004: GHz and THz properties of graphene and graphene patch antennas David Carey, Mojtaba Dashti The distinctive band structure of graphene allows for both inter- and intra-band contributions to sheet conductivity at different energy and frequency scales. Here we report the variation of 2D sheet conductivity and related electronic properties of single layer graphene in the GHz to THz regime. We identify the different contributions to conduction of both the real and imaginary part of the 2D sheet conductivity as function of temperature, chemical potential and scattering time within the random-phase approximation. With knowledge of the high frequency variation of the 2D sheet conductivity, a circular microstrip graphene patch antenna with a central frequency of 2 THz has been designed. We report the factors that control the antenna frequency, bandwidth as well as the voltage standing wave ratio, radiation efficiency, and the radiation pattern of both the electric and magnetic field components. Comparison with a similar copper patch antenna demonstrates the advantages of using graphene. The prospects for graphene based antennas operating in the THz part of the spectrum are also discussed. [Preview Abstract] |
Wednesday, March 15, 2017 8:48AM - 9:00AM |
K31.00005: Observation of Gate-Tunable Coherent Perfect Absorption of Terahertz Waves in Graphene Coskun Kocabas, Nurbek Kakenov, Osman Balci, Taylan Takan, Vedat Ali Ozkan, Hakan Altan We report experimental observation of electrically tunable coherent perfect absorption (CPA) of terahertz (THz) radiation in graphene. We develop a reflection-type tunable THz cavity formed by a large-area graphene layer, a metallic reflective electrode, and an electrolytic medium in between. Ionic gating in the THz cavity allows us to tune the Fermi energy of graphene up to 1 eV and to achieve a critical coupling condition at 2.8 THz with absorption of 100 {\%}. With the enhanced THz absorption, we were able to measure the Fermi energy dependence of the transport scattering time of highly doped graphene. Furthermore, we demonstrate flexible active THz surfaces that yield large modulation in the THz reflectivity with low insertion losses. We anticipate that the gate-tunable CPA will lead to efficient active THz optoelectronics applications. [Preview Abstract] |
Wednesday, March 15, 2017 9:00AM - 9:12AM |
K31.00006: Ultrafast Electron Dynamics in hBN-Encapsulated Graphene Steven Drapcho, Long Ju, Guorui Chen, Yinchuan Lv, Ilyoun Na, Yuanbo Zhang, Feng Wang We perform ultrafast transient absorption spectroscopy on high quality graphene encapsulated in hexagonal boron nitride and non-encapsulated graphene on a silicon-silicon dioxide substrate, using a near-IR pump and a mid-IR probe. We measure the transient absorption signal as a function of graphene doping and pump fluence for both room temperature and 77K, and compare our results to models taking into account the interband and intraband electronic transitions in graphene. We compare our experimental carrier lifetimes to theoretical models to investigate the electron decay mechanisms in high quality graphene. [Preview Abstract] |
Wednesday, March 15, 2017 9:12AM - 9:24AM |
K31.00007: Control of ultrafast electron dynamics in graphene by the shape of the optical pulse Seyyedeh Azar Oliaei Motlagh, Vadym Apalkov, Mark Stockman We study theoretically the interband and intraband electron dynamics in graphene, a layer of one atom thick carbon, in the presence of an ultrafast optical pulse. The electron system is described within the effective low energy Dirac Hamiltonian for graphene near $K$ and $K'$ points in the first Brillouin zone. After the pulse, a nonzero residual conduction band population shows high irreversibility of electron dynamics. Our calculations show that the distribution of residual conduction band populations in the reciprocal space strongly depends on the profile of the pulse and the number of oscillations of the field in the pulse. We also calculated the transferred charge for optical pulses of different shapes. Our computations demonstrate that the dependence of the transferred charge on the pulse's amplitude is strongly affected by the pulse waveform, i.e., by the number of oscillations within the pulse. For one oscillation of the optical field, the transferred charge has a monotonic dependence on the amplitude of the pulse, while for many oscillations of the field, the transferred charge shows oscillatory behavior as a function of the pulse's amplitude. [Preview Abstract] |
Wednesday, March 15, 2017 9:24AM - 9:36AM |
K31.00008: Layer-Dependent Third-Harmonic Generation in Graphene Hao Yang, Honghua Guan, Jerry Dadap, Richard Osgood Graphene has become a subject of intense interest and study because of its remarkable 2D electronic properties. Multilayer graphene also offers an array of properties that are also of interest for optical physics and devices. Despite its second-order-nonlinear optical response is intrinsically weak, third-order nonlinear optical effects in graphene are symmetry-allowed thus leading to studies of several third-order process in few-layer graphene. In this work, we report third-harmonic generation in multilayer graphene mounted on fused silica and with thicknesses which approach the bulk continuum. THG signals show cubic power dependence with respect to the intensity of fundamental beam. Third-harmonic generation spectroscopy enables a good fit using linear optical detection, which shows strong contrast for different layer number graphene. The maximum THG efficiency appears at layer number around 30. Two models are used for describing this layer dependent phenomenon and shows absorption plays a key role in THG of multilayer graphene. This work also provides a new imaging technology for graphene detection and identification with better contrast and resolution. [Preview Abstract] |
Wednesday, March 15, 2017 9:36AM - 9:48AM |
K31.00009: Electrically controlled magnetic circular dichroism and Faraday rotation in graphene. Alexey Kuzmenko, Jean-Marie Poumirol, Peter Q. Liu Liu, Tetiana Slipchenko, Alexey Nikitin, Luis Martin-Moreno, Jerome Faist Magnetic circular dichroism (MCD) and Faraday rotation (FR) are the fundamental phenomena of great practical importance arising from the breaking of the time reversal symmetry by a magnetic field. In most materials the strength and the sign of these effects can be only controlled by the field value and its orientation. Using broadband terahertz magneto-electro-optical spectroscopy, we demonstrate that in graphene both the MCD and the FR can be modulated in intensity, tuned in frequency and, importantly, inverted using only electrostatic doping at a fixed magnetic field due to the unique properties of the Dirac fermions. Our results indicate the fundamental possibility of compact, efficient, electrically invertible and wavelength-tunable non-reciprocal passive terahertz elements based on graphene operating at ambient temperature. [Preview Abstract] |
Wednesday, March 15, 2017 9:48AM - 10:00AM |
K31.00010: Ultrafast electron diffraction study of ab-plane dynamics in superconducting Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+d}$ Tatiana Konstantinova, Alexander Reid, Lijun Wu, Hermann Durr, Xijie Wang, Yimei Zhu The role of phonons and other collective modes in cooperative electron phenomena in high-T$_{C}$ cuprate superconductors is an extensively interesting topic. Time-resolved experiments provide temporal hierarchy of the bosonic modes interacting with electrons. However, majority of research in this field explore dynamics of electronic states and can only make indirect conclusion about involvement of the lattice. We report time-resolved study of optimally doped Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+d}$ lattice response to photo-excitation by means of ultrafast electron diffraction that is directly sensitive to atomic motion. Data analysis utilizing Bloch-wave calculation of diffraction peak intensity allows separation of Cu-O in-plane vibration building up on the sub picosecond time scale from the low energy phonon population growth with a much slower rate. This study confirms the assumption of strong electron coupling to the Cu-O plane phonons. [Preview Abstract] |
Wednesday, March 15, 2017 10:00AM - 10:12AM |
K31.00011: Ultrafast photocurrents in monolayer MoS$_2$ Eric Parzinger, Ursula Wurstbauer, Alexander W. Holleitner Two-dimensional transition metal dichalcogenides such as MoS$_2$ have emerged as interesting materials for optoelectronic devices. In particular, the ultrafast dynamics and lifetimes of photoexcited charge carriers have attracted great interest during the last years. We investigate the photocurrent response of monolayer MoS$_2$ on a picosecond time scale utilizing a recently developed pump-probe spectroscopy technique based on coplanar striplines. We discuss the ultrafast dynamics within MoS$_2$ including photo-thermoelectric currents and the impact of built-in fields due to Schottky barriers as well as the Fermi level pinning at the contact region. [Preview Abstract] |
Wednesday, March 15, 2017 10:12AM - 10:24AM |
K31.00012: Fast Photo-detection in Phototransistors based on Group III-VI Layered Materials. Prasanna Patil, Sujoy Ghosh, Milinda Wasala, Sidong Lei, Robert Vajtai, Pulickel Ajayan, Saikat Talapatra Response time of a photo detector is one of the crucial aspect of photo-detection. Recently it has been shown that direct band gap of few layered group III-VI materials helps in increased absorption of light thereby enhancing the photo responsive properties of these materials. Ternary system of Copper Indium Selenide has been extensively used in optoelectronics industry and it is expected that 2D layered structure of Copper Indium Selenide will be a key component of future optoelectronics devices based on 2D materials. Here we report fast photo detection in few layers of Copper Indium Selenide (CuIn$_{7}$Se$_{11})$ phototransistor. Few-layers of CuIn$_{7}$Se$_{11}$ flakes were exfoliated from crystals grown using chemical vapor transport technique. Our photo response characterization indicates responsivity of 10$^{4}$ mA/W with external quantum efficiency exceeding 10$^{3}$. We have found response time of few $\mu $s which is one of the fastest response among photodetectors based on 2D materials. We also found specific detectivity of \textasciitilde 10$^{12}$ Jones which is an order higher than conventional photodetectors. A comparison between response times of various layered group III-VI materials will be presented and discussed. This work is supported by the U.S. Army Research Office through a MURI grant {\#} W911NF-11-1-0362. [Preview Abstract] |
Wednesday, March 15, 2017 10:24AM - 10:36AM |
K31.00013: Ultrafast resolution of photocurrent generation bottlenecks in stacked van der Waals materials Kyle Vogt, Sufei Shi, Feng Wang, Matt Graham Combining E-Field dependent ultrafast photocurrent and transient absorption microscopy, we determine the fundamental electron extraction rates that determine photocurrent efficiency in stacked WSe$_{2}$ devices. We find that both measurement techniques yield the same rate limited ultrafast time constant of 87 ps, associated with exciton dissociation and electron escape. Using the corresponding the recombination rates, we can calculate the upper bound of IQE in our device to be $\sim$51$\%$ which agrees with our directly measured ‘on-chip’ photoefficiency. [Preview Abstract] |
Wednesday, March 15, 2017 10:36AM - 10:48AM |
K31.00014: Continuous-wave Landau-level laser in graphene Alexey Belyanin, Yongrui Wang, Mikhail Tokman We prove the general feasibility and demonstrate the design of a continuous-wave terahertz laser operating between Landau levels in graphene placed on a polar substrate. Steady state population inversion under a continuous wave optical pumping becomes possible due to surface-phonon mediated relaxation of carriers. Our microscopic kinetics simulations including all relevant scattering processes show the existence of a steady state gain of magnitude up to 5{\%} per monolayer. The laser concept is transferable to other materials with massless Dirac fermions, notably to surface states in 3D topological insulators such as Bi$_{\mathrm{2}}$Se$_{\mathrm{3}}$. [Preview Abstract] |
Wednesday, March 15, 2017 10:48AM - 11:00AM |
K31.00015: Photon-assisted shot noise in graphene in the Terahertz range Francois Parmentier, Laura Serkovic-Loli, Preden Roulleau, Christian Glattli When subjected to electromagnetic radiation, the fluctuation of the electronic current across a quantum conductor increases. This additional noise, called photon-assisted shot noise, arises from the generation and subsequent partition of electron-hole pairs in the conductor. The physics of photon-assisted shot noise has been thoroughly investigated at microwave frequencies up to 20 GHz, and its robustness suggests that it could be extended to the terahertz (THz) range. Here, we present measurements of the quantum shot noise generated in a graphene nanoribbon subjected to a THz radiation. Our results show signatures of photon-assisted shot noise, further demonstrating that hallmark time-dependant quantum transport phenomena can be transposed to the THz range.\\ F.D. Parmentier \textit{et al.}, Phys. Rev. Lett. \textbf{116,} 227401 (2016). [Preview Abstract] |
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