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  • Journal article
    Zhao W, Wang S, Liu B, Verzhbitskiy I, Li S, Giustiniano F, Kozawa D, Loh KP, Matsuda K, Okamoto K, Oulton RF, Eda Get al., 2016,

    Exciton-Plasmon Coupling and Electromagnetically Induced Transparency in Monolayer Semiconductors Hybridized with Ag Nanoparticles

    , Advanced Materials, Vol: 28, Pages: 2709-2715, ISSN: 1521-4095
  • Journal article
    Wilkinson JT, Whitehouse CB, Oulton RF, Gennaro SDet al., 2016,

    An undergraduate experiment demonstrating the physics of metamaterials with acoustic waves and soda cans

    , American Journal of Physics, Vol: 84, Pages: 14-20, ISSN: 0002-9505

    We describe a novel undergraduate research project that highlights the physics of metamaterials withacoustic waves and soda cans. We confirm the Helmholtz resonance nature of a single can bymeasuring its amplitude and phase response to a sound wave. Arranging multiple cans in arrayssmaller than the wavelength, we then design an antenna that redirects sound into a preferred direction.The antenna can be thought of as a new resonator, composed of artificially engineered meta-atoms,similar to a metamaterial. These experiments are illustrative, tactile, and open ended so as to enablestudents to explore the physics of matter/wave interaction

  • Journal article
    Nielsen MP, Lafone L, Rakovich A, Sidiropoulos TP, Rahmani M, Maier SA, Oulton RFet al., 2016,

    Adiabatic Nanofocusing in Hybrid Gap Plasmon Waveguides on the Silicon-on-Insulator Platform.

    , Nano Letters, Vol: 16, Pages: 1410-1414, ISSN: 1530-6992

    We present an experimental demonstration of a new class of hybrid gap plasmon waveguides on the silicon-on-insulator (SOI) platform. Created by the hybridization of the plasmonic mode of a gap in a thin metal sheet and the transverse-electric (TE) photonic mode of an SOI slab, this waveguide is designed for efficient adiabatic nanofocusing simply by varying the gap width. For gap widths greater than 100 nm, the mode is primarily photonic in character and propagation lengths can be many tens of micrometers. For gap widths below 100 nm, the mode becomes plasmonic in character with field confinement predominantly within the gap region and with propagation lengths of a few microns. We estimate the electric field intensity enhancement in hybrid gap plasmon waveguide tapers at 1550 nm by three-photon absorption of selectively deposited CdSe/ZnS quantum dots within the gap. Here, we show electric field intensity enhancements of up to 167 ± 26 for a 24 nm gap, proving the viability of low loss adiabatic nanofocusing on a commercially relevant photonics platform.

  • Journal article
    Schnitzer O, Giannini V, Craster RV, Maier SAet al., 2016,

    Asymptotics of surface-plasmon redshift saturation at subnanometric separations

    , Physical Review B, Vol: 93, ISSN: 1550-235X

    Many promising nanophotonics endeavors hinge upon the unique plasmonic properties of nanometallic structures with narrow nonmetallic gaps, which support superconcentrated bonding modes that singularly redshift with decreasing separations. In this Rapid Communication, we present a descriptive physical picture, complemented by elementary asymptotic formulas, of a nonlocal mechanism for plasmon redshift saturation at subnanometric gap widths. Thus, by considering the electron-charge and field distributions in the close vicinity of the metal-vacuum interface, we show that nonlocality is asymptotically manifested as an effective potential discontinuity. For bonding modes in the near-contact limit, the latter discontinuity is shown to be effectively equivalent to a widening of the gap. As a consequence, the resonance-frequency near-contact asymptotics are a renormalization of the corresponding local ones. Specifically, the renormalization furnishes an asymptotic plasmon-frequency lower bound that scales with the 1/4 power of the Fermi wavelength. We demonstrate these remarkable features in the prototypical cases of nanowire and nanosphere dimers, showing agreement between our elementary expressions and previously reported numerical computations.

  • Journal article
    Colombi A, Roux P, Guenneau S, Gueguen P, Craster RVet al., 2016,

    Forests as a natural seismic metamaterial: Rayleigh wave bandgaps induced by local resonances

    , Scientific Reports, Vol: 6, ISSN: 2045-2322

    We explore the thesis that resonances in trees result in forests acting as locally resonant metamaterials for Rayleigh surface waves in the geophysics context. A geophysical experiment demonstrates that a Rayleigh wave, propagating in soft sedimentary soil at frequencies lower than 150 Hz, experiences strong attenuation, when interacting with a forest, over two separate large frequency bands. This experiment is interpreted using finite element simulations that demonstrate the observed attenuation is due to bandgaps when the trees are arranged at the sub-wavelength scale with respect to the incident Rayleigh wave. The repetitive bandgaps are generated by the coupling of the successive longitudinal resonances of trees with the vertical component of the Rayleigh wave. For wavelengths down to 5 meters, the resulting bandgaps are remarkably large and strongly attenuating when the acoustic impedance of the trees matches the impedance of the soil. Since longitudinal resonances of a vertical resonator are inversely proportional to its length, a man-made engineered array of resonators that attenuates Rayleigh waves at frequency ≤10 Hz could be designed starting from vertical pillars coupled to the ground with longitudinal resonance ≤10 Hz.

  • Journal article
    Hamm JM, Page AF, Bravo-Abad J, Garcia-Vidal FJ, Hess Oet al., 2016,

    Nonequilibrium plasmon emission drives ultrafast carrier relaxation dynamics in photoexcited graphene

    , Physical Review B, Vol: 93, ISSN: 1550-235X

    The fast decay of carrier inversion in photoexcited graphene has been attributed to optical phonon emission and Auger recombination. Plasmon emission provides another pathway that, as we show here, drives the carrier relaxation dynamics on ultrafast timescales. In studying the nonequilibrium relaxation dynamics we find that plasmon emission effectively converts inversion into hot carriers, whose energy is then extracted by optical phonon emission. This mechanism not only explains the observed fs-lifetime of inversion but also offers the prospect for atomically thin ultrafast plasmon emitters.

  • Journal article
    Makwana M, Antonakakis T, Maling B, Guenneau S, Craster RVet al., 2016,

    Wave mechanics in media pinned at bravais lattice points

    , SIAM Journal on Applied Mathematics, Vol: 76, Pages: 1-26, ISSN: 1095-712X

    The propagation of waves through microstructured media with periodically arrangedinclusions has applications in many areas of physics and engineering, stretching from photonic crystalsthrough to seismic metamaterials. In the high-frequency regime, modeling such behavior iscomplicated by multiple scattering of the resulting short waves between the inclusions. Our aimis to develop an asymptotic theory for modeling systems with arbitrarily shaped inclusions locatedon general Bravais lattices. We then consider the limit of pointlike inclusions, the advantage beingthat exact solutions can be obtained using Fourier methods, and go on to derive effective mediumequations using asymptotic analysis. This approach allows us to explore the underlying reasons fordynamic anisotropy, localization of waves, and other properties typical of such systems, and in particulartheir dependence upon geometry. Solutions of the effective medium equations are comparedwith the exact solutions, shedding further light on the underlying physics. We focus on examplesthat exhibit dynamic anisotropy as these demonstrate the capability of the asymptotic theory to pickup detailed qualitative and quantitative features.

  • Conference paper
    Shibanuma T, Albella P, Maier SA, 2016,

    Efficient directional control of scattered field at optical frequency with subwavelength asymmetric dielectric dimers

    , 10th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics (METAMATERIALS), Publisher: IEEE, Pages: 331-333
  • Journal article
    Zhao R, Luo Y, Pendry JB, 2016,

    Transformation optics applied to van der Waals interactions

    , SCIENCE Bulletin, Vol: 61, Pages: 59-67, ISSN: 2095-9273

    The van der Waals force originates from the electromagnetic interaction between quantum fluctuation-induced charges. It is a ubiquitous but subtle force which plays an important role and has a wide range of applications in surface related phenomena like adhesion, friction, and colloidal stability. Calculating the van der Waals force between closely spaced metallic nanoparticles is very challenging due to the strong concentration of electromagnetic fields at the nanometric gap. Especially, at such a small length scale, the macroscopic description of the dielectric properties no longer suffices. The diffuse nonlocal nature of the induced surface electrons which are smeared out near the boundary has to be considered. Here, we review the recent progress on using three-dimensional transformation optics to study the van der Waals forces between closely spaced nanostructures. Through mapping a seemingly asymmetric system to a more symmetric counterpart, transformation optics enables us to look into the behavior of van der Waals forces at extreme length scales, where the effect of nonlocality is found to dramatically weaken the van der Waals interactions.

  • Journal article
    Duffin TJ, Nielsen MP, Diaz F, Palomba S, Maier SA, Oulton RFet al., 2015,

    Degenerate four-wave mixing in silicon hybrid plasmonic waveguides

    , Optics Letters, Vol: 41, Pages: 155-158, ISSN: 1539-4794

    Silicon-based plasmonic waveguides show high confinementwell beyond the diffraction limit. Various deviceshave been demonstrated to outperform their dielectriccounterparts at micrometre scales, such as linearmodulators, capable of generating high field confinementand improving device efficiency by increasingaccess to nonlinear processes, limited by ohmiclosses. By using hybridised plasmonic waveguide architecturesand nonlinear materials, silicon-based plasmonicwaveguides can generate strong nonlinear effectsover just a few wavelengths. We have theoreticallyinvestigated the nonlinear optical performance of twohybrid plasmonic waveguides (HPWG) with three differentnonlinear materials. Based on this analysis, thehybrid gap plasmon waveguide (HGPW), combinedwith the DDMEBT nonlinear polymer, shows a fourwavemixing (FWM) conversion efficiency of 16.4dBover a 1mm propagation length, demonstrating that plasmonicwaveguides can be competitive with standardsilicon photonics structures over distances three ordersof magnitude shorter.

  • Journal article
    Levy U, Berini P, Maier SA, Mortensen NAet al., 2015,

    Focus Issue on surface plasmon photonics introduction

    , OPTICS EXPRESS, Vol: 23, Pages: 32075-32079, ISSN: 1094-4087
  • Journal article
    Albella P, Shibanuma T, Maier S, 2015,

    Switchable directional scattering of electromagnetic radiation with subwavelength asymmetric silicon dimers

    , Scientific Reports, Vol: 5, ISSN: 2045-2322

    High refractive index dielectric nanoparticles show high promise as a complementary nanophotonics platform due to compared with plasmonic nanostructures low absorption losses and the co-existence of magnetic and electric resonances. Here we explore their use as resonantly enhanced directional scatterers.We theoretically demonstrate that an asymmetric dimer of silicon nanoparticles shows tuneable directional scattering depending on the frequency of excitation. This is due to the interference between dipoles excited in each nanoparticle, enabling directional control of the scattered light. Interestingly, this control can be achieved regardless of the polarization direction with respect to the dimer axis; however, difference in the polarization can shift the wavelengths at which the directional scattering is achieved. We also explore the application of such an asymmetric nanoantenna as a tuneable routing element in a nanometer scale a full numerical simulation, suggesting applications in optical nanocircuitry.

  • Journal article
    Pusch A, Oh S, Wuestner S, Roschuk T, De Luca A, Chen Y, Boual S, Ali Z, Phillips C, Hong M, Maier S, Udrea F, Hopper R, Hess Oet al., 2015,

    A highly efficient CMOS nanoplasmonic crystal enhanced slow-wave thermal emitter improves infrared gas-sensing devices

    , Scientific Reports, Vol: 5, ISSN: 2045-2322

    The application of plasmonics to thermal emitters is generally assisted by absorptive losses in the metal because Kirchhoff’s law prescribes that only good absorbers make good thermal emitters. Based on a designed plasmonic crystal and exploiting a slow-wave lattice resonance and spontaneous thermal plasmon emission, we engineer a tungsten-based thermal emitter, fabricated in an industrial CMOS process, and demonstrate its markedly improved practical use in a prototype non-dispersive infrared (NDIR) gas-sensing device. We show that the emission intensity of the thermal emitter at the CO2 absorption wavelength is enhanced almost 4-fold compared to a standard non-plasmonic emitter, which enables a proportionate increase in the signal-to-noise ratio of the CO2 gas sensor.

  • Journal article
    Wood JJ, Lafone L, Hamm JM, Hess O, Oulton RFet al., 2015,

    Plasmonic CROWs for Tunable Dispersion and High Quality Cavity Modes

    , Scientific Reports, Vol: 5, ISSN: 2045-2322

    Coupled resonator optical waveguides (CROWs) have the potential to revolutionise integrated optics, to slow-light and enhance linear and non-linear optical phenomena. Here we exploit the broad resonances and subwavelength nature of localized surface plasmons in a compact CROW design where plasmonic nanoparticles are side coupled to a dielectric waveguide. The plasmonic CROW features a low loss central mode with a highly tunable dispersion, that avoids coupling to the plasmonic nanoparticles close to the band-edge. We show that this low loss character is preserved in finite plasmonic CROWs giving rise to Fabry-Perot type resonances that have high quality factors of many thousands, limited only by the CROW length. Furthermore we demonstrate that the proposed CROW design is surprisingly robust to disorder. By varying the geometric parameters one can not only reduce the losses into dissipative or radiative channels but also control the outcoupling of energy to the waveguide. The ability to minimise loss in plasmonic CROWs while maintaining dispersion provides an effective cavity design for chip-integrated laser devices and applications in linear and non-linear nano-photonics.

  • Journal article
    Luo Y, Fernandez-Dominguez AI, Wiener A, Maier SA, Pendry JBet al., 2015,

    Reply to "Comment on “Surface Plasmons and Nonlocality: A Simple Model”

    , Physical Review Letters, Vol: 115, ISSN: 1079-7114
  • Journal article
    Ceresoli L, Abdeddaim R, Antonakakis T, Maling B, Chmiaa M, Sabouroux P, Tayeb G, Enoch S, Craster RV, Guenneau Set al., 2015,

    Dynamic effective anisotropy: Asymptotics, simulations, and microwave experiments with dielectric fibers

    , PHYSICAL REVIEW B, Vol: 92, ISSN: 1098-0121

    We investigate dynamic effective anisotropy in photonic crystals (PCs) through a combination of an effective medium theory, which is a high-frequency homogenization (HFH) method explicitly developed to operate for short waves, as well as through numerical simulations and microwave experiments. The HFH yields accurate predictions of the effective anisotropic properties of periodic structures when the wavelength is of comparable order to the pitch of the array; specifically, we investigate a square array of pitch 2 cm consisting of dielectric rods of radius 0.5 cm and refractive index n=6√ within an air matrix. This behaves as an effective medium, with strong artificial anisotropy, at a frequency corresponding to a flat band emerging from a Dirac-like point in transverse magnetic (TM) polarization. At this frequency, highly directive emission is predicted for an electric source placed inside this PC, and this artificial anisotropy can be shown to coincide with a change of character of the underlying effective equation from isotropic to unidirective, with coefficients of markedly different magnitudes appearing in the effective equation tensor. In transverse electric (TE) polarization, we note a second radical change of character of the underlying effective equation, this time from elliptic to hyperbolic, near a frequency at which a saddle point occurs in the corresponding dispersion curves. Delicate microwave experiments are performed in both polarizations for such a PC consisting of 80 rods, and we demonstrate that a directive emission in the form of a + (respectively, an X) is indeed seen experimentally at the predicted frequency 9.5 GHz in TM polarization (respectively, 5.9 GHz in TE polarization). These are clearly dynamic effects since in the quasistatic regime the PC just behaves as an isotropic medium.

  • Journal article
    Quintanilla FH, Fan Z, Lowe MJS, Craster RVet al., 2015,

    Guided waves' dispersion curves in anisotropic viscoelastic single- and multi-layered media

    , Proceedings of the Royal Society A: Mathematical, Physical & Engineering Sciences, Vol: 471, ISSN: 1471-2946

    Guided waves propagating in lossy media are encountered in many problems across different areas of physics such as electromagnetism, elasticity and solid-state physics. They also constitute essential tools in several branches of engineering, aerospace and aircraft engineering, and structural health monitoring for instance. Waveguides also play a central role in many non-destructive evaluation applications. It is of paramount importance to accurately represent the material of the waveguide to obtain reliable and robust information about the guided waves that might be excited in the structure. A reasonable approximation to real solids is the perfectly elastic approach where the frictional losses within the solid are ignored. However, a more realistic approach is to represent the solid as a viscoelastic medium with attenuation for which the dispersion curves of the modes are, in general, different from their elastic counterparts. Existing methods are capable of calculating dispersion curves for attenuated modes but they can be troublesome to find and the solutions are not as reliable as in the perfectly elastic case. In this paper, in order to achieve robust and accurate results for viscoelasticity a spectral collocation method is developed to compute the dispersion curves in generally anisotropic viscoelastic media in flat and cylindrical geometry. Two of the most popular models to account for material damping, Kelvin–Voigt and Hysteretic, are used in various cases of interest. These include orthorhombic and triclinic materials in single- or multi-layered arrays. Also, and due to its importance in industry, a section is devoted to pipes filled with viscous fluids. The results are validated by comparison with those from semi-analytical finite-element simulations.

  • Journal article
    Ottobre M, Pavliotis GA, Pravda-Starov K, 2015,

    Some remarks on degenerate hypoelliptic Ornstein-Uhlenbeck operators

  • Journal article
    Kraft M, Luo Y, Maier SA, Pendry JBet al., 2015,

    Designing plasmonic gratings with transformation optics

    , Physical Review X, Vol: 5, ISSN: 2160-3308

    Plasmonic gratings that support both localized and propagating plasmons have wide applications in solar cells and optical biosensing. In this paper, we report on a most unusual grating designed to capture light efficiently into surface plasmons and concentrate their energy at hot spots where the field is resonantly enhanced. The dispersion of the surface plasmons shows degeneracy points at k=0, where, despite a strongly modulated grating, hidden symmetries forbid hybridization of plasmons traveling in opposite directions.

  • Journal article
    Lei DY, Appavoo K, Ligmajer F, Sonnefraud Y, Haglund RF, Maier SAet al., 2015,

    Optically-Triggered Nanoscale Memory Effect in a Hybrid Plasmonic-Phase Changing Nanostructure

    , ACS PHOTONICS, Vol: 2, Pages: 1306-1313, ISSN: 2330-4022
  • Journal article
    Liu W, Oulton RF, Kivshar YS, 2015,

    Geometric interpretations for resonances of plasmonic nanoparticles

    , Scientific Reports, Vol: 5, ISSN: 2045-2322

    The field of plasmonics can be roughly categorized into two branches: surface plasmon polaritons (SPPs) propagating in waveguides and localized surface plasmons (LSPs) supported by scattering particles. Investigations along these two directions usually employ different approaches, resulting in more or less a dogma that the two branches progress almost independently of each other, with few interactions. Here in this work we interpret LSPs from a Bohr model based geometric perspective relying on SPPs, thus establishing a connection between these two sub-fields. Besides the clear explanations of conventional scattering features of plasmonic nanoparticles, based on this geometric model we further demonstrate other anomalous scattering features (higher order modes supported at lower frequencies, and blueshift of the resonance with increasing particle sizes) and multiple electric resonances of the same order supported at different frequencies, which have been revealed to originate from backward SPP modes and multiple dispersion bands supported in the corresponding plasmonic waveguides, respectively. Inspired by this geometric model, it is also shown that, through solely geometric tuning, the absorption of each LSP resonance can be maximized to reach the single channel absorption limit, provided that the scattering and absorption rates are tuned to be equal.

  • Journal article
    Daskalakis KS, Maier SA, Kena-Cohen S, 2015,

    Spatial Coherence and Stability in a Disordered Organic Polariton Condensate

    , PHYSICAL REVIEW LETTERS, Vol: 115, ISSN: 0031-9007
  • Journal article
    Tufarelli T, McEnery KR, Maier SA, Kim MSet al., 2015,

    Signatures of the A2 term in ultrastrongly coupled oscillators

    , Physical Review A, Vol: 91, ISSN: 1094-1622

    We study a bosonic matter excitation coupled to a single-mode cavity field via electric dipole. Counter-rotating and A2 terms are included in the interaction model, A being the vector potential of the cavity field. In the ultrastrong coupling regime the vacuum of the bare modes is no longer the ground state of the Hamiltonian and contains a nonzero population of polaritons, the true normal modes of the system. If the parameters of the model satisfy the Thomas-Reiche-Kuhn sum rule, we find that the two polaritons are always equally populated. We show how this prediction could be tested in a quenching experiment, by rapidly switching on the coupling and analyzing the radiation emitted by the cavity. A refinement of the model based on a microscopic minimal coupling Hamiltonian is also provided, and its consequences on our results are characterized analytically.

  • Journal article
    Roeder R, Sidiropoulos TPH, Tessarek C, Christiansen S, Oulton RF, Ronning Cet al., 2015,

    Ultrafast Dynamics of Lasing Semiconductor Nanowires

    , Nano Letters, Vol: 15, Pages: 4637-4643, ISSN: 1530-6992

    Semiconductor nanowire lasers operate at ultrafast timescales; here we report their temporal dynamics, including laser onset time and pulse width, using a double-pump approach. Wide bandgap gallium nitride (GaN), zinc oxide (ZnO), and cadmium sulfide (CdS) nanowires reveal laser onset times of a few picoseconds, driven by carrier thermalization within the optically excited semiconductor. Strong carrier–phonon coupling in ZnO leads to the fastest laser onset time of ∼1 ps in comparison to CdS and GaN exhibiting values of ∼2.5 and ∼3.5 ps, respectively. These values are constant between nanowires of different sizes implying independence from any optical influences. However, we demonstrate that the lasing onset times vary with excitation wavelength relative to the semiconductor band gap. Meanwhile, the laser pulse widths are dependent on the optical system. While the fastest ultrashort pulses are attained using the thinnest possible nanowires, a sudden change in pulse width from ∼5 to ∼15 ps occurs at a critical nanowire diameter. We attribute this to the transition from single to multimode waveguiding, as it is accompanied by a change in laser polarization.

  • Journal article
    Shi F, Choi W, Lowe MJS, Skelton EA, Craster RVet al., 2015,

    The validity of Kirchhoff theory for scattering of elastic waves from rough surfaces

  • Journal article
    Chen Y, Li X, Luo X, Maier SA, Hong Met al., 2015,

    Tunable near-infrared plasmonic perfect absorber based on phase-change materials

    , PHOTONICS RESEARCH, Vol: 3, Pages: 54-57
  • Journal article
    Kalliadasis S, Krumscheid S, Pavliotis GA, 2015,

    A new framework for extracting coarse-grained models from time series with multiscale structure

    , Journal of Computational Physics, Vol: 296, Pages: 314-328, ISSN: 1090-2716

    In many applications it is desirable to infer coarse-grained models from observational data. The observed process often corresponds only to a few selected degrees of freedom of a high-dimensional dynamical system with multiple time scales. In this work we consider the inference problem of identifying an appropriate coarse-grained model from a single time series of a multiscale system. It is known that estimators such as the maximum likelihood estimator or the quadratic variation of the path estimator can be strongly biased in this setting. Here we present a novel parametric inference methodology for problems with linear parameter dependency that does not suffer from this drawback. Furthermore, we demonstrate through a wide spectrum of examples that our methodology can be used to derive appropriate coarse-grained models from time series of partial observations of a multiscale system in an effective and systematic fashion.

  • Journal article
    Gilbertson AM, Francescato Y, Roschuk T, Shautsova V, Chen Y, Sidiropoulos TPH, Hong M, Giannini V, Maier SA, Cohen LF, Oulton RFet al., 2015,

    Plasmon-Induced Optical Anisotropy in Hybrid Graphene-Metal Nanoparticle Systems

    , NANO LETTERS, Vol: 15, Pages: 3458-3464, ISSN: 1530-6984
  • Journal article
    Colquitt DJ, Craster RV, Makwana M, 2015,


  • Journal article
    Okell WA, Witting T, Fabris D, Arrell CA, Hengster J, Ibrahimkutty S, Seiler A, Barthelmess M, Stankov S, Lei DY, Sonnefraud Y, Rahmani M, Uphues T, Maier SA, Marangos JP, Tisch JWGet al., 2015,

    Temporal broadening of attosecond photoelectron wavepackets from solid surfaces

    , Optica, Vol: 2, Pages: 383-387, ISSN: 2334-2536

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