Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session M56: Collective Modes and Optical Nonlinearities in GrapheneRecordings Available
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Sponsoring Units: DCMP Chair: Ken Burch, Boston College Room: Hyatt Regency Hotel -Burnham |
Wednesday, March 16, 2022 8:00AM - 8:12AM |
M56.00001: Subharmonic intersubband polaritonic responses in metagate-tuned strongly-modulated graphene Minwoo Jung, Gennady Shvets We show that an extreme modulation of carrier density in monolayer graphene deforms the underlying Dirac band dispersion and results in subharmonic inter-subband transition responses in optical conductivity. In our proposed system, hBN-encapsulated graphene is placed on top of a one-dimensional metagate with a periodicity of $L$. Besides the metagate-tuning, a backgate placed beneath the metagate is used as the second gate, further modulating carrier density on regions in graphene that are not directly screened by the metagate. With strong carrier density modulation, graphene optical conductivity, computed by Kubo formula applied to deformed electronic band structures, shows resonances at frequencies $\nu v_F G_0$, where $\nu=0.5,1,1.5,...$, $v_F$ is the fermi velocity of Dirac electrons, and $G_0$ is the reciprocal lattice vector $2\pi/L$. We find that these half-integer subharmonic resonances are caused by transitions between subbands that are equispaced by $0.5v_F G_0$ near the fermi sea. As a result, there appear new polaritonic peaks in far-field reflection spectra that cannot be predicted by local or perturbative-nonlocal graphene conductivity models. Our study opens up an avenue for exploring emergent polaritons in two-dimensional materials with engineered band structures. |
Wednesday, March 16, 2022 8:12AM - 8:24AM |
M56.00002: Nanoscale THz Spectroscopy of Electrically Gated Graphene Nanoribbons Melanie Dieterlen, Erin Sheridan, Pubudu Wijesinghe, Patrick Irvin, Jeremy Levy, Ki-Tae Eom, Chang-Beom Eom, Alexander Sinitskii Graphene nanoribbons (GNRs) have shown many interesting electrical and optical properties that are enabled by the bottom-up synthetic chemistry. We have developed a novel optical spectrometer capable of probing the nonlinear optical response of nanoparticles with dimensions ~10 nm or less, over a wide range of frequencies in THz and NIR [1]. The experiments take advantage of strong nonlinearities in SrTiO3 and the ability to “write” conductive nanowires at the LaAlO3/SrTiO3 (LAO/STO) interface, with ~10 nm gaps that are co-located with a single GNR. We probe GNRs individually under the influence of large electric fields (~1 MV/cm) with various geometries of electric gates aligned parallel and perpendicular to the length of the GNR. The voltage-gated band structure changes are expected to play an important role in developing GNR-based spin qubits. |
Wednesday, March 16, 2022 8:24AM - 8:36AM |
M56.00003: Cryogenic THz Nano Imaging and Spectroscopy of Graphene/α-RuCl3Heterostructures Rocco A Vitalone, Daniel J Rizzo, Bjarke S Jessen, Ran Jing, Brian S Kim, David G Mandrus, Cory R Dean, James C Hone, Dmitri N Basov Several recent studies have shown that graphene can be heavily doped via a charge transfer process when it shares an interface with a number of different materials. One such material is α-RuCl3, which has been shown to dope graphene to a Fermi energy of roughly 0.6 eV. One question of interest is what effect this charge transfer process has on α-RuCl3. Namely, is α-RuCl3 doped into a metallic state. To investigate this claim, we probe graphene/ α-RuCl3 heterostructures in the low-energy THz regime to understand how their Drude characteristics differ from pristine graphene. Using our home-built cryogenic microscope, we image a graphene/ α-RuCl3 stack using THz light and extract local spectra from 0.5 - 1.5 THz, all with nanoscale resolution. In our nanoimaging measurements, we observe clear contrast between the three different regions of our heterostructure stack: graphene/RuCl3, graphene, and α-RuCl3. Changes in contrast is evidence of substantial changes in the number of Drude carriers between the three regions. Further, at physical graphene edges on α-RuCl3, we observe local contrast in both amplitude and phase, which is indicative of a local plasmonic response. Finally, we will report the analysis of nano-spectra of both graphene/α-RuCl3 and graphene. |
Wednesday, March 16, 2022 8:36AM - 8:48AM |
M56.00004: Cyclotron resonance overtones and near-field magnetoabsorption via terahertz Bernstein modes in graphene Denis A Bandurin, Erwin Moench, Kirill Kapralov, Isabelle Y Phinney, Katja Lindner, Song Liu, James H Edgar, Ivan A Dmitriev, Pablo Jarillo-Herrero, Dmitry Svintsov, Sergey Ganichev 2D electron systems subjected to a perpendicular magnetic field absorb electromagnetic radiation via the cyclotron resonance (CR). In this presentation, we will discuss a qualitative breach of this well-known behavior in graphene. Our study of the THz photoresponse reveals a resonant burst at the main overtone of the CR, drastically exceeding the signal due to the ordinary CR. In accordance with the developed theory, the photoresponse dependencies on the magnetic field, doping level, and sample geometry suggest that the origin of this anomaly lies in the near-field magnetoabsorption facilitated by the Bernstein modes, ultra-slow magnetoplasmonic excitations reshaped by nonlocal electron dynamics. These modes are characterized by a diverging plasmonic density of states that strongly amplifies the radiation absorption. Our results show that the radiation absorption via nonlocal collective modes can facilitate a strong photoresponse, a behavior potentially useful for IR and THz technology. |
Wednesday, March 16, 2022 8:48AM - 9:00AM |
M56.00005: Surface plasmons induce topological transition in graphene/MoO3 heterostructures Francesco L Ruta, Brian S Kim, Zhiyuan Sun, Daniel J Rizzo, Alexander S McLeod, Anjaly Rajendran, Song Liu, Andrew J Millis, James C Hone, Dmitri N Basov Polaritons in hyperbolic van der Waals materials – where principal axes have permittivities of opposite signs – have helped develop new nanotechnologies, study fundamental nano-optics, and probe complex response functions. The isofrequency contours of hyperbolic polaritons may undergo topological transitions from open hyperbolas to closed ellipse-like curves, prompting a discontinuous change in physical properties. Electronically-tunable topological transitions are especially desirable for future integrated technologies but have yet to be demonstrated. In this work, we present a doping-induced topological transition effected by plasmon-phonon hybridization in a graphene/MoO3 heterostructure. Scanning near-field optical microscopy was used to image hybrid polaritons in graphene/MoO3. We demonstrate the topological transition and characterize the hybrid modes, studying their evolution from surface waves to bulk waveguide modes and the dependence of properties of hybrid polaritons on plasmon-phonon coupling strength. Graphene/MoO3 is an exciting platform for exploring dynamical topological transitions and directional plasmon-phonon coupling in nanophotonics. |
Wednesday, March 16, 2022 9:00AM - 9:12AM |
M56.00006: Atomically imprinted graphene plasmonic cavities Brian S Kim, Aaron Sternbach, Min Sup Choi, Zhiyuan Sun, Francesco L Ruta, Alexander S McLeod, Lin Xiong, Yinan Dong, Anjaly Rajendran, Song Liu, Ankur Nipane, Sang Hoon Chae, Xiaodong Xu, Andrew J Millis, P J Schuck, Cory R Dean, James C Hone, Dmitri N Basov The ability to design spatial patterns of high carrier density in two-dimensional materials with nanoscale cavity and circuitry features underlies future progress in nonlinear nanophotonics and strong light-matter interactions. Here, we present a general strategy to atomically imprint low-loss graphene plasmonic structures using oxidation-activated charge transfer (OCT). We covered charge-neutral graphene with a monolayer of WSe2, which is subsequently oxidized into a high work-function monolayer WOx to activate charge transfer. Our nano-infrared imaging reveals low-loss plasmon polaritons at the WOx/graphene interface. We insert WSe2 spacers to precisely control the OCT-induced carrier density and to achieve near-intrinsic quality factor of plasmons. Finally, we highlight canonical examples of plasmonic cavities imprinted via programmable OCT, exhibiting laterally abrupt doping profiles with single-digit nanoscale precision. In particular, we demonstrated technologically appealing but elusive plasmonic whispering-gallery resonators based on graphene using OCT-induced free-standing photonic platforms. Our results open avenues for novel quantum photonic architectures incorporating two-dimensional materials. |
Wednesday, March 16, 2022 9:12AM - 9:24AM |
M56.00007: Plasmonics in a graphene cavity Johannes Geurs, Yinan Dong, Dmitri N Basov, Cory R Dean The interaction between light and matter leads to a wide variety of polaritonic phenomena [1]. The confinement of these excitations in van der Waals heterostructures has allowed the direct imaging of surface plasmon polaritons (SPPs), and the effects of gating, sample boundaries and interfaces with different materials [2,3]. |
Wednesday, March 16, 2022 9:24AM - 9:36AM |
M56.00008: Detecting sum-frequency-generated light from gated graphene nanostructures and nanoribbons Pubudu G Wijesinghe, Erin Sheridan, Melanie Dieterlen, Patrick Irvin, Jeremy Levy, Ki-Tae Eom, Chang-Beom Eom Graphene nanostructures and nanoribbons exhibit remarkable nonlinear optical behavior when subjected to intense local electric fields [1,2]. In some instances, signatures of high harmonic generation have been detected in graphene [3], while second harmonic generation and difference frequency mixing is routinely observed. The experimental signatures of these nonlinear processes are detected through interferometric methods [4]. We describe efforts to directly measure blue light emanating from graphene and graphene nanoribbons that are gated at ~10 nm scales. The detection of sum-frequency-generated light in the far field would help in the quantification of these effects. |
Wednesday, March 16, 2022 9:36AM - 9:48AM |
M56.00009: Giant enhancement of third-harmonic generation in graphene–metal heterostructures Philipp K Jenke Nano-optical plasmonic structures have the potential to amplify nonlinear processes by efficiently focusing far-field light into small sub-wavelength volumes. Two dimensional materials such as graphene are promising candidates for nonlinear optoelectronic applications due to their strong intrinsic and electrically tunable optical nonlinear response, while supporting plasmonic excitations. Here, enhance the third-order optical nonlinear response of graphene–insulator–metal heterostructures by three orders of magnitude with respect to bare graphene. We achieve this using metallic nanoribbons to simultaneously launch acoustic graphene plasmons and enhance the far field pump light in the graphene layer. Furthermore, by manipulating the electrical environment we can modulate the nonlinear optical signal. This work shows the potential of nonlinear processes driven by graphene plasmons in graphene–insulator–metal heterostructures for optically controlled and electrically tunable nano-optoelectronic components, compatible with established nanofabrication techniques. |
Wednesday, March 16, 2022 9:48AM - 10:00AM |
M56.00010: Fermi level dependence of ultrafast time-resolved luminescence from single-layer graphene Daiki Inukai, Takeshi Koyama, Kenji Kawahara, Hiroki Ago, Hideo Kishida The photoluminescence (PL) from single-layer graphene has been observed under femtosecond laser pulse excitation. The PL is expected to depend on the Fermi level (EF). An elucidation of the EF dependence of PL intensity is important from the viewpoint of future device applications. In this research, we focus on the ultrafast PL from graphene in the near-infrared energy region and clarify the EF dependence of the PL intensity. To control the EF of graphene, we used the electrochemical doping technique using an ionic liquid [EMIM][TFSI]. We measured the time-resolved PL using the frequency up-conversion method. The experiments were performed with excitation energy of 1.55 eV and emission energy of 0.9 eV. Here, the EF of graphene was varied from approximately -0.6 eV to +0.2 eV. We observed a change in the PL intensity with doping level. Based on the results, we discuss the origin of the PL depending on the Fermi level. |
Wednesday, March 16, 2022 10:00AM - 10:12AM |
M56.00011: Graphene-based nanoscale attosecond light source Erin C Sheridan, Melanie Dieterlen, Aditi Nethwewala, Qing Guo, Muqing Yu, Ki-Tae Eom, Chang-Beom Eom, Patrick R Irvin, Jeremy Levy High harmonic generation (HHG) is an extreme nonlinear optical process in which multiple harmonics of a pump laser frequency are emitted from strongly driven carriers. The unique physics of two-dimensional materials and surfaces such as graphene offers new routes to achieving HHG within the solid-state. Extreme ultraviolet (XUV) HHG sources, in particular, will allow for the study of attosecond dynamics in quantum systems. To date, extreme ultraviolet HHG has not been observed in graphene. We report the experimental observation of XUV HHG in monolayer graphene integrated with electrically biased LaAlO3/SrTiO3 nanoscale junctions. Both odd and even harmonics of VIS-NIR pump frequencies are generated up to the 15th harmonic with energy ~22 eV. HHG is observed at input peak intensities orders of magnitude lower than the pump powers required in many previous studies. To our knowledge, this is the first demonstration of XUV HHG in graphene. |
Wednesday, March 16, 2022 10:12AM - 10:24AM |
M56.00012: Nonlinear optical response of Twisted Bilayer graphene Leone Di Mauro Villari, Alessandro Principi In recent years the interest on graphene based Moire systems has spiked due to discovery of high temperature superconductivity for specific twisting angles. The nonlinear response of such systems to ultra-short pulses, however also represents a very promising field due to the possibility of engineering optical properties through twisting. We characterise the nonlinear optical current spectrum of twisted bilayer graphene in the kp approximation, for different twisting angles. We do this by using the Dirac-Bloch equations (DBEs), a non perturbative version of the semiconductor Bloch equations. The DBEs, used for the first time in 2010 by Ishikawa to study the optical properties of graphene are a powerful tool as they allow to obtain both the interband and intraband optical response relatively easily. We investigate the generation of high harmonics and the emergence of even harmonics when the Moire-bands low energy Hamiltonian breaks the inversion symmetry. In particular we analyse the behaviour of the nonlinear current when flat bands appear which is expected to change quite dramatically due to Berry curvature hotspots and reduced quasiparticle velocities. |
Wednesday, March 16, 2022 10:24AM - 10:36AM |
M56.00013: Theoretical Modeling of Collective Mode Effects in Photocurrent Nanoscopy Andrey A Rikhter, Michael M Fogler, Dmitri N Basov Utilizing scanned probes to focus light beyond the diffraction limit has been shown to be effective for studying collective modes of two-dimensional plasmonic and polaritonic systems, such as graphene and van der Waals heterostructures. |
Wednesday, March 16, 2022 10:36AM - 10:48AM |
M56.00014: Spin-valley Silin modes in graphene with substrate-induced spin-orbit coupling Zachary M Raines, Dmitrii Maslov, Leonid Glazman In the presence of an external magnetic field the Fermi-liquid state supports oscillatory spin modes known as Silin modes. We predict the existence of the generalized Silin modes in a multivalley system, monolayer graphene. Along with the spin, the generalized Silin modes may involve the valley degree of freedom. A gauge- and Berry-gauge- invariant kinetic equation for a multivalley Fermi liquid is developed and applied to the case of graphene with extrinsic spin-orbit coupling (SOC). The interplay of SOC and Berry curvature allows for the excitation of generalized Silin modes in the spin and valley-staggered-spin channels via an AC electric field. The resonant contributions from these modes to the optical conductivity are calculated. |
Wednesday, March 16, 2022 10:48AM - 11:00AM |
M56.00015: Realising time-reversal forbidden photocurrents in non-magnetic materials Ying Xiong, Li-kun Shi, Justin Song Time-reversal symmetry severely constrains the nonlinear optical responses in materials. For example, time-reversal forbidden photocurrents (e.g. linear injection and circular shift photocurrents) have been conventionally thought to only manifest parity violating magnetis such as those of found in antiferromagnets. Here, we propose that by coupling with plasmonic fields, non-vertical interband transitions unblock such time-reversal forbidden photocurrents even in materials that preserve both inversion and time-reversal symmetries. Furthermore, these non-vertical photocurrents exhibit a resonant peak when charge carriers near the Fermi surface are photoexcited. Such Fermi surface resonant effect enables selective sampling of part of the Fermi surface, leading to giant enhancement of optical nonlinearity as well as an ARPES-like photocurrent probe to investigate the quantum geometric properties in non-magnetic and centro-symmetric materials. |
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