Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session L03: Strong Light-matter Coupling and Enhanced Spectroscopy: Strong Coupling IFocus
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Sponsoring Units: DCP DAMOP Chair: Joel Yuen-Zhou, Univ of California - San Diego Room: LACC 150C |
Wednesday, March 7, 2018 11:15AM - 11:51AM |
L03.00001: The Alchemy of Vacuum - Hybridizing Light and Matter Invited Speaker: Thomas Ebbesen Strong coupling of light and matter can give rise to a multitude of exciting physical effects through the formation of hybrid light-matter states. When molecular materials with high transition dipole moments are placed in the confined fields of metallic microcavities or surface plasmons, Rabi splittings approaching 1 eV are observed due to the interaction with the vacuum electromagnetic field. This leads to fundamental changes in the properties of the coupled system, especially in the ultra-strong coupling regime. While strong coupling has been extensively studied due to the potential it offers in physics such as room temperature polariton condensates and thresholdless lasers, the implications for molecular and material science have remained mostly unexplored. After introducing the fundamental concepts, examples of modified properties of strongly coupled systems, such as chemical reactivity and charge and energy transport, will be given to illustrate the potential of light-matter states.1-9 |
Wednesday, March 7, 2018 11:51AM - 12:03PM |
L03.00002: Room-temperature superfluidity of organic polaritons Stephane Kena-Cohen, Giovanni Lerario, Antonio Fieramosca, Fabio Barachati, Kostantinos Daskalakis, Dario Ballarini, Daniele Sanvitto Exciton-polaritons are hybrid light-matter particles that can be created in semiconductor microcavities. These quasiparticles can possess enhanced third-order nonlinearities as compared to bare photons due to the resonant behaviour and the matter component. In this work, we will demonstrate the superfluid flow of polaritons at room-temperature in an organic microcavity. These observations are a result of the strong polariton-polariton nonlinearities present in such structures. Polaritons can be selectively created with a fixed flow velocity and observed to flow in the sample plane. When the density of a polariton condensate is increased, its excitation spectrum acquires a linear shape around the pump wavevector, which is related to the sound velocity for elementary excitations. When this sound velocity increases beyond the flow velocity, scattering becomes disallowed in agreement with the Landau criterion for superfluidity. This transition is observed for flow across defects in the sample both in real space and in phase space as a function of the polariton density. The prospect of creating devices that are immune from scattering is attractive for future room-temperature polaritonic devices. |
Wednesday, March 7, 2018 12:03PM - 12:15PM |
L03.00003: Controlling Chemistry with Cavity Quantum Electrodynamics Felipe Herrera, Frank Spano The demonstration of strong and ultrastrong coupling regimes of cavity QED with organic molecules has opened new routes to control chemical dynamics at the nanoscale. Based on the Holstein-Tavis-Cummings (HTC) model of organic cavities, we prove analytically and confirm numerically that strong resonant cavity-molecule coupling can effectively decouple electronic and nuclear degrees of freedom in a disordered molecular ensemble. This type of polaron decoupling effectively prevents nuclear reorganization in the excited electronic state, and can potentially influence charge and energy transfer processes in molecular ensembles. As an example, we show that polaron decoupling can lead to an exponential enhancement of intramolecular electron transfer rates between donor and acceptor groups in comparison with free-space reactions, which may find applications in the development of novel optoelectronic devices. |
Wednesday, March 7, 2018 12:15PM - 12:51PM |
L03.00004: Strong coupling of single molecules in plasmonic nano- and pico-cavities Invited Speaker: Rohit Chikkaraddy Coupling between plasmonic metal nano-components generates strongly red-shifted resonances combined with intense local field amplification on the nanoscale. This allows directly seeing individual molecules as well as excitations in monolayer semiconductors. We have explored plasmonic coupling which can be tuned dynamically, through reliable bottom-up self-assembly using the nanoparticle-on-mirror geometry (NPoM) [1-5]. We recently demonstrated how precisely placed individual molecules can be strongly coupled to these ultralow volume plasmonic cavities as well as how they act as optomechanical constructs with enormously enhanced coupling. We also demonstrate the possibility to track few molecules using the extreme enhancements. We are able to watch individual electrons hopping onto and off molecules in the gap, and watch redox processes in real time. |
Wednesday, March 7, 2018 12:51PM - 1:03PM |
L03.00005: Control of Vibration-Cavity Polaritons in the Frequency and Time Domains Blake Simpkins, Adam Dunkelberger, Kenan Fears, Wonmi Ahn, Igor Vurgaftman, Jeffrey Owrutsky We focus on light-matter interactions to alter the chemical behavior of molecular species. Strong coupling to molecular vibrations creates vibrational polaritons enabling modified energetics and, potentially, the ability to control chemical reactivity and energy relaxation. We will describe strong coupling between a Fabry-Pérot cavity and several molecular species (e.g., polymers and solvated species) and investigate the transition from the strong to weak coupling regimes. We map the influence of molecule/cavity mode overlap by systematically altering the position of a molecular slab throughout the first and second order cavity. In the time domain, pump-probe infrared spectroscopy is used to characterize the dynamics of vibration-cavity polaritons revealing quantum beats and excited-state absorption from polaritons and uncoupled reservoir modes. Polaritons relax ten times more quickly than uncoupled vibrations and exhibit a cavity tuning-dependent lifetime due to mixed cavity and molecular character of the polariton. Since energy relaxation depends on cavity-vibration coupling, it may provide opportunities to influence chemical reactivity. |
Wednesday, March 7, 2018 1:03PM - 1:15PM |
L03.00006: Revealing Hidden Vibration-Cavity Polariton Interactions by 2D IR Spectroscopy Bo Xiang, Raphael Ribeiro, Adam Dunkelberger, Jiaxi Wang, Yingmin Li, Blake Simpkins, Jeffrey Owrutsky, Joel Yuen-Zhou, Wei Xiong We report the first two-dimensional infrared (2D IR) spectroscopy of new molecular photonic materials – vibrational polaritons. The 2D IR technique is unique in its ability to reveal interactions and state-selective resolving of hybrid light-matter excitations and dark states. Comparing to 2D IR of pure molecular systems, 2D IR of vibrational polariton show drastic different spectral features which are definite evidences of dark states and interactions between dark states and polaritons. This finding is different from the prevalent optical model of polariton derived from linear spectroscopy, which only considers the upper and lower polaritons. Furthermore, our results highlight role of vibrational anharmonicities in generating the observed non-linear signals and disproves the notion that vibration-polaritons are free harmonic Bosons. This work reveals polariton physics that are otherwise difficult to be probed by traditional linear spectroscopy and lay foundations for novel nonlinear optics and polariton chemistry of vibrational polariton. |
Wednesday, March 7, 2018 1:15PM - 1:51PM |
L03.00007: Modified excited states dynamics in the localized plasmon - molecular exciton hybrids Invited Speaker: Timur Shegai Strong light-matter interactions in microcavities have been long known to provide means to alter optical and nonlinear properties of the coupled system. As a result of this interaction, one typically observes the emergence of new polaritonic eigenstates. These states are of hybrid nature and possess both light and matter characteristics, which is reflected in vacuum Rabi splitting, observed in the absorption or transmission spectra. Because of the compositional nature of these states, the excited state temporal dynamics can be significantly altered in comparison to the uncoupled system dynamics. This, in turn, can have profound effects on the emission and photochemical processes. |
Wednesday, March 7, 2018 1:51PM - 2:03PM |
L03.00008: Laser-Induced Transmission on Ultrafast Timescales via Vibrational Strong Coupling Adam Dunkelberger, Roderick Davidson, Wonmi Ahn, Blake Simpkins, Jeffrey Owrutsky Strong coupling between vibrational modes and cavity optical modes leads to the formation of vibration-cavity polaritons, separated by the vacuum Rabi splitting. The splitting depends on the square root of the concentration of absorbers confined in the cavity. This dependence has important implications on the response of the coupled system after ultrafast infrared excitation. In this work, we report on solutions of W(CO)6 in hexane with concentration chosen to access a regime that borders on weak coupling. Under these conditions, huge fractions of the W(CO)6 oscillators can be excited, and the anharmonicity of the molecules leads to a commensurate reduction in the Rabi splitting. We report excitation fractions >0.8 and show drastic increases in transmission that can be modulated on the picosecond timescale. In comparison to previous experiments, the transient spectra we observe are much simpler because excited-state transitions lie outside the transmission spectrum of the cavity and, so, give much smaller contributions to the spectra. We find that the Rabi splitting recovers with the vibrational relaxation lifetime of uncoupled W(CO)6, implying that polaritons are not directly involved in the relaxation after the first few ps. |
Wednesday, March 7, 2018 2:03PM - 2:15PM |
L03.00009: Correlated Electron-Photon Excitations within Quantum Electrodynamical Density-functional Theory Davis Welakuh, Johannes Flick, Michael Ruggenthaler, Heiko Appel, Angel Rubio Novel experiments in cavity QED is at the interface between quantum optics and chemistry. Ab initio methods that treats an interacting many-electron system coupled to photons on an equal quantized footing has been developed and it's termed Quantum-Electrodynamical Density-Functional theory (QEDFT) [1]. The Kohn-Sham scheme of QEDFT has been used to study ground-state properties of an interacting electron-photon system [2]. Here, we present an ab-initio linear-response (LR) formalism that allows to calculate excited states phenomena for general matter-photon coupled systems. Beside the usual density-density response function known in time-dependent DFT, we have three new response functions due to coupling matter to photons. We reformulate the response functions and develop a numerically feasible and tractable pseudo-eigenvalue problem for the coupled electron-photon system. We present first principle calculations for excited state properties for a specific molecule coupled to a cavity photon. Furthermore, we show using LR in QEDFT that Maxwell's equation for coupled matter-photon system are modified. |
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