Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session C12: 2D Materials (General): Transport and Optical Phenomena -- Light-Matter Interactions |
Hide Abstracts |
Sponsoring Units: DMP Chair: Luis Jauregui, Harvard University Room: BCEC 153A |
Monday, March 4, 2019 2:30PM - 2:42PM |
C12.00001: Indirect bandgap measured in β'-phase In2Se3 crystals by angle-resolved photoemission spectroscopy Michael Fuhrer, James Collins, Chutian Wang, Anton Tadich, Yuefeng Yin, Shujie Tang, Sung-Kwan Mo, Chang Liu, Changxi Zheng, Nikhil Medhekar, Mark T Edmonds In2Se3 is a widely studied van der Waals (vdW) layered material and its many structural phases have attracted attention for their promise as semiconducting platforms for photovoltaics, use as an isostructural buffer layers in topological Insulator superlattices, and recently as room temperature ferroelectrics1,2. The details of its electronic structure however have not been fully elucidated by experiments. We report on a combined angle-resolved photoemission spectroscopy and density functional theory study which reveals an indirect bandgap with highly anisotropic conduction and valence bands in bulk crystals of commercially obtained β'-phase In2Se3. The n-doped crystals exhibit large effective mass hole bands with maxima slightly offset from Γ, as well as small effective mass electron valleys which sit at Γ and M/M' points, with minima at M/M’ lower in energy by about 0.3eV, resulting in an indirect bandgap of 1.41eV, and a direct bandgap at Γ in excess of 1.7eV. |
Monday, March 4, 2019 2:42PM - 2:54PM |
C12.00002: Theory of “Emergence of excitonic superfluid at topological-insulator surfaces” Rui Wang, Yasen Hou, Rui Xiao, Luke McClintock, Henry Clark Travaglini, John Paulus Francia, Harry Fetsch, Onur Erten, Sergey Savrasov, Baigeng Wang, Antonio Rossi, Inna Vishik, Eli Rotenberg, Dong Yu We study the BCS condensation of excitons on topological-insulator surfaces. With presence of a screened Coulomb interaction between excited electrons and holes, the BCS excitons can be formed with predicted transition temperature up to 40K. The thermal fluctuation is found to disturb the long-range order by creating vortex excitations. It lowers the mean-field estimation of the transition temperature and drives the transition into the Kosterlitz-Thouless type. The BCS condensation of excitons forms ground state with quantum coherence that leads to the experimentally observed long-range transport of photocurrent. We also discuss possible generation of the topological p+ip excitonic insulators at topological-insulator surfaces. |
Monday, March 4, 2019 2:54PM - 3:06PM |
C12.00003: Optical Selection Rules and Optical Nonlinearities of Excitonic States in Monolayer MoS2 Daniel Soh, Eric Chatterjee, Christopher Rogers, Dodd J Gray, Hideo Mabuchi The monolayer MoS2 exhibits a strong optical response from the stable excitonic states even at room temperature, due to the large binding energy of the reduced dimension. We present that the topological chirality in MoS2 binding the valleys and the spins determines not only the linear but also the nonlinear optical responses. Using the massive Dirac Hamiltonian to provide efficient handling of the nonlinear processes, we perform a perturbative calculation in the low-temperature and weakly excited limit. We then derive the linear and the nonlinear optical susceptibilities. We calculated those for particularly the second- and the third-harmonic generations, two-photon absorption, and optical Kerr effect, based on the prescribed optical selection rules. We compare the optical responses of the monolayer MoS2 with our previous results on graphene, adopting the Keldysh-type wave functions and the S-matrix treatment. We also present the figure of merit for efficient optical Kerr device applications. |
Monday, March 4, 2019 3:06PM - 3:18PM |
C12.00004: Photoluminescence studies of monolayer WSe2 in proximity with BiFeO3 thin films. Anil Rajapitamahuni, Nerea Ontoso, Saeedeh Farokhipoor, Jose Ignacio Pascual, Beatriz Noheda, Reyes Calvo We have studied the photoluminescence (PL) properties of 1-layer WSe2 in proximity with multiferroic BiFeO3 (BFO) thin films. Using pulsed laser deposition, we have grown epitaxial single crystalline BFO films of 20 -80 nm thick on SrRuO3 buffered (001) SrTiO3 substrates. X -Ray and AFM characterizations show the films have high crystallinity and smooth surface. Piezo-response force microscopy studies show that the as-grown PZT films have uniform polarization pointing away from the substrate. We then transferred WSe2 flakes onto 300 nm SiO2 and BFO using elastic film assisted micro-mechanical exfoliation. Optical microscopy combined with Raman spectroscopy is used to identify and determine the layer number of WSe2 flakes. Spatially-resolved PL spectroscopy measurements are performed using a scanning confocal microscope to investigate the valley excitonic properties of WSe2 in proximity with BFO. When compared to SiO2, we observed a quenching in PL signal for WSe2 on BFO at 300 K. We have also studied the effect of temperature and magnetic fields on the valley polarization of monolayer WSe2 in proximity with multiferroic BFO thin films. |
Monday, March 4, 2019 3:18PM - 3:30PM |
C12.00005: Tunable Optical Absorption by Excitons in Xenes via an External Electric Field Matthew Brunetti, Oleg Berman, Roman Kezerashvili We study the binding energies and optical properties of direct and indirect excitons in monolayers and double-layer heterostructures of Xenes: silicene, germanene, and stanene. The exciton eigenenergies, optical transition energy, oscillator strength, and absorption coefficient are calculated [1]. An external electric field tunes the eigenenergies and optical properties of excitons by changing the effective mass of charge carriers. The Schrödinger equation with field-dependent exciton reduced mass is solved by using the Rytova-Keldysh (RK) potential for direct excitons, while both the RK and Coulomb potentials are used for indirect excitons. For indirect excitons, we show that the choice of interaction potential can cause significant changes in the eigenenergies. Finally, our results show that the choice of material parameters has a significant effect on the binding energies and optical properties of direct and indirect excitons. These calculations contribute to the rapidly growing body of research regarding the excitonic and optical properties of this new class of two-dimensional semiconductors. |
Monday, March 4, 2019 3:30PM - 3:42PM |
C12.00006: Emergence of excitonic superfluid at topological-insulator surfaces Yasen Hou, Rui Wang, Rui Xiao, Luke McClintock, Henry Clark Travaglini, John Paulus Francia, Harry Fetsch, Onur Erten, Sergey Savrasov, Baigeng Wang, Antonio Rossi, Inna Vishik, Eli Rotenberg, Dong Yu Excitons are spin integer particles that were predicted to condense into a coherent quantum state at sufficiently low temperature more than 50 years ago. Nonetheless, transport of exciton condensates is not yet understood and it is unclear whether an exciton condensate is a superfluid or an insulating electronic crystal. Topological insulators (TIs) with massless particles and unique spin textures have been theoretically predicted as a promising platform for achieving exciton condensation. Here we report experimental evidence of excitonic superfluid phase at the surface of three-dimensional (3D) TIs. We unambiguously confirmed that electrons and holes are paired into charge neutral bound states by the electric field independent photocurrent distributions. And we observed a millimetre-long transport distance of these excitons up to 40 K, which strongly suggests dissipationless propagation. The robust macroscopic quantum states achieved with simple device architecture and broadband photoexcitation at relatively high temperature are expected to find novel applications in quantum computations and spintronics. |
Monday, March 4, 2019 3:42PM - 3:54PM |
C12.00007: Interlayer exciton diffusion in MoSe2/WSe2 heterostructures Junho Choi, Wei-Ting Hsu, Li-Shuan Lu, Hui-Yu Cheng, Liuyang Sun, Kha Tran, André Zepeda, Marshall Campbell, Matthew Staab, Kayleigh R Jones, Takashi Taniguchi, Kenji Watanabe, Chih-Kang Shih, Xiaoqin (Elaine) Li, Wen-Hao Chang Excitons with large binding energy are formed in atomically thin semiconductors because of the insufficient dielectric screening outside of the 2D layers. In a vertical heterostructure consisting of MoSe2 and WSe2 monolayers, the type-II band alignment leads to the rapid transfer of electron to the MoSe2 layer and hole to the WSe2 layer, forming interlayer excitons with drastically different properties than excitons confined within one monolayer. We investigate the interlayer exciton diffusion in MoSe2/WSe2 heterostructures. We compare a mechanically stacked heterostructure with hexagonal boron nitride (hBN) encapsulation and one grown by chemical vapor deposition (CVD). Spatially and time-resolved photoluminescence measurements are performed at low-temperature. Interlayer exciton diffusion length and coefficient are extracted in both heterostructures and found to be rather different. |
Monday, March 4, 2019 3:54PM - 4:06PM |
C12.00008: Valley Selective Optical Routing in Hyperbolic Metamaterials Sriram Guddala, Mandeep Khatoniar, Nicholas Yama, Vinod M Menon At the monolayer limit, the 2D transition metal dichalcogenides materials such as WS2, WSe2, and MoS2 etc., are endowed with direct bandgap and high binding energy excitons at individually addressable two degenerate valleys in momentum space at K and K' points in the first Brillouin zone. In recent years, there has been growing interest in achieving control over the selective valley excitation/emission by means of optical, electrical, and magnetic fields and explore this valley degree of freedom as an efficient way of data transfer, computing and storage technology, called valleytronics. We describe and experimentally demonstrate the optical control on selective valley excitation and emission routing through spatially confined subwavelength electromagnetic modes in an anisotropic metamaterial with hyperbolic dispersion. The directionality of selective valley exciton emission depends on the handedness of that valley’s circular polarization emission. The demonstrated capability of our hyperbolic metamaterial -TMD hybrid system is free from precise nanoscale structural dimensions and most importantly broadband response and shows great potential to develop prototype devices such as valley filters or valley-based qubits for quantum computing/communications. |
Monday, March 4, 2019 4:06PM - 4:18PM |
C12.00009: Non-adiabatic effects in exciton-mediated Raman scattering from first principles Sven Reichardt, Ludger Wirtz, Andrea Marini We present a fully quantum mechanical, ab initio approach for the calculation of optical properties of solids, in particular resonant Raman scattering. Starting from the fundamental observable, we derive a fully general description of light scattering by matter beyond the commonly used semi-classical approximations for the electron-nuclei interaction. Our approach captures both direct and phonon-mediated light absorption as well as inelastic light scattering. |
Monday, March 4, 2019 4:18PM - 4:30PM |
C12.00010: Probing the nonlinear response of strongly coupled plasmon-WSe2 system Chentao Li, Hayk Harutyunyan, Xin Lu, Ajit Srivastava Two-dimentional transition metal dichalcogenides (TMDs) have recently emerged as a class of material that shows a great potential for strong light-matter interaction at the nanoscale. Signatures of strong coupling, such as Rabi-splitting in the linear optical spectra, have been observed by placing TMDs in optical nanocavities. Typically, plasmonic nanocavities and nanostructures are used to reach the appropriate parameters for the observation of strong coupling regime. However, most studies utilize dark field (DF) scattering experiments rather than photoluminescence (PL) for the demonstration of strong coupling phenomena, whereas the observation of PL splitting in this system has rarely been reported. Thus, more convincing evidences of strong coupling are still needed. |
Monday, March 4, 2019 4:30PM - 4:42PM |
C12.00011: Probing the phonon scattering in the strong light-matter coupling regime Xiaoze Liu, Jun Yi, Sui Yang, Erh-chen Lin, Yue-Jiao Zhang, Jian-Feng Li, Yuan Wang, Yi-Hsien Lee, Zhong-Qun Tian, Xiang Zhang The strong light-matter coupling is the core of cavity quantum electrodynamics (CQED), which leads to discoveries of fascinating phenomena in solid state system such as Bose-Einstein condensation and photon blockade. Indirect evidence indicates non-fluorescence processes such as phonon scattering are critical to these phenomena. However, the understanding of such processes remains elusive due to their non-radiative nature smeared by the overwhelming fluorescence in cavities. Here we directly probe phonon scattering based on Raman spectroscopy in the strong coupling regime in a plasmonic cavity embedded with a monolayer MoS2. The studied non-fluorescence process is significantly modified by the hybrid properties of the newly formed half-light half-matter quasiparticles, i.e., polaritons. For the first time, we observe nonlinearly enhanced valley-dependent phonon modes, involved with stimulated lattice vibrations and inter-valley scatterings. This work provides a new perspective to investigate fundamental quantum processes in the strong coupling regime. |
Monday, March 4, 2019 4:42PM - 4:54PM |
C12.00012: Ultra-long wavelength Dirac plasmons in graphene capacitors David Mele, Holger Graef, Michael Rosticher, Luca Banszerus, Christoph Stampfer, Takashi Taniguchi, Kenji Watanabe, Erwann Bocquillon, Gwendal Fève, Jean-Marc Berroir, Edwin Hang Tong Teo, Bernard Plaçais Graphene is a recognized 2D platform for plasmonics in the THz and mid-IR domains. These high-energy plasmons couple to the dielectric surface modes, giving rise to hybrid plasmon-polariton excitations. The ultra-long wavelength GHz range addresses the low energy end of the spectrum, where Dirac plasmons are damped by ohmic losses but essentially decoupled from environment. Using hBN encapsulated graphene [1], we demonstrate a plasma resonance capacitor [2] showing a quarter-wave plasmon mode, at 40 GHz, with a quality factor Q=2. The resolution of the resonant technique yields precise determinations of the electronic compressibility, kinetic inductance, and mean free-path, in good agreement with theory. The 100µm-long wavelength allows engineering of doping-modulated devices where plasmons are controlled by Klein tunneling. Downscaling for room temperature operation opens up perspectives in microwave detection for wireless communication and sensing [3]. |
Monday, March 4, 2019 4:54PM - 5:06PM |
C12.00013: Strong coupling in metal-WS2 hybrid system Jinwei Shi, Dahe Liu, Chih-Kang Shih, Yi-Hsien Lee, Shangjr Gwo Metallic particle array as an effective plasmonic cavity has attracted great interest. Coupling between such plasmonic cavity and gain materials have been reported. In this work, we studied two kinds of polaritons in such system. First, we studied the strong coupling between groove localized surface plasmon resonance (LSPR) and lattice surface plasmon polariton in a metallic groove array. We found that the optical response of such system is different from the ordinary weak coupling surface lattice resonance. A giant Rabi splitting of ~440 meV was observed, both angle and pitch tuning. The underlying mechanism is analyzed. Next, we studied the coupling between the metallic grating and the exciton in WS2 monolayer. LSPR was used. The parallel electric field within the groove can provide an effective coupling to the excitons of monolayer WS2. To overcome the problem of angle tuning reported in previous work, we developed a depth chirped grating to realize the resonance tuning. A moderate Rabi splitting of 56 meV was observed. These works demonstrate the potential application in strong coupling devices based on plasmonic cavity. |
Monday, March 4, 2019 5:06PM - 5:18PM |
C12.00014: Optical absorption spectra of monolayer transition metal dichalcogenides at high doping levels Minda Deng, Chun-Lan Wu, Ziliang Ye, Yi Cui, Tony F Heinz The absorption spectra of semiconducting transition metal dichalcogenides (TMDCs) at monolayer thickness are dominated by excitonic transitions due to the strong Coulomb interactions associated with the materials’ reduced screening and dimensionality. It has been shown that the excitons in these materials can be tuned electrically by using a Si back gate to achieve carrier density up to several times 1012cm-2. Here we extend these studies to higher carrier densities through the use of electric double layer gating technique with the ionic solid conductor LaF3 as the electrolyte. In this fashion, we are able to electrostatically gate monolayer WSe2 to a density of a few 1013cm-2. While earlier investigations showed shifts in exciton (and charged exciton) energies and binding energies, the excitonic absorption features remained relatively strong and distinct. At carrier densities in the 1013cm-2 range, however, we find that the excitonic absorption features are no longer observable. The progression of the measured absorption spectra with increasing doping density is compatible with the behavior expected for a Mott transition from the excitonic regime to an electron–hole plasma regime, as was previously reported for the case of strong photodoping of TMDC monolayers. |
Monday, March 4, 2019 5:18PM - 5:30PM |
C12.00015: Nonperturbative nonlinear eects in the dispersion relations for TE and TM plasmons on two-dimensional materials Vera Andreeva, Mitchell Luskin, Dionisios Margetis We analytically obtain the dispersion relations for transverse-electric (TE) and transverse-magnetic (TM) surface plasmon-polaritons in a nonlinear two-dimensional (2D) conducting material with inversion symmetry lying between two Kerr-type dielectric media. To this end, we use Maxwell’s equations within the quasielectrostatic, weakly dissipative regime. We show that the wavelength and propagation distance of surface plasmons decrease due to the nonlinearity of the surrounding dielectric. In contrast, the eect of the nonlinearity of the 2D material depends on the signs of the real and imaginary parts of the third-order conductivity. Notably, the dispersion relations obtained by naively replacing the permittivity of the dielectric medium by its nonlinear counterpart in the respective dispersion relations of the linear regime are not accurate. We apply our analysis to the case of doped graphene and make predictions for the TM-polarized surface plasmon wavelength and propagation distance. |
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