42 results found
Proctor M, Xiao X, Craster RV, et al., 2020, Near- and Far-Field Excitation of Topological Plasmonic Metasurfaces, Photonics, Vol: 7, Pages: 81-81
<jats:p>The breathing honeycomb lattice hosts a topologically non-trivial bulk phase due to the crystalline-symmetry of the system. Pseudospin-dependent edge states, which emerge at the interface between trivial and non-trivial regions, can be used for the directional propagation of energy. Using the plasmonic metasurface as an example system, we probe these states in the near- and far-field using a semi-analytical model. We provide the conditions under which directionality was observed and show that it is source position dependent. By probing with circularly-polarised magnetic dipoles out of the plane, we first characterise modes along the interface in terms of the enhancement of source emissions due to the metasurface. We then excite from the far-field with non-zero orbital angular momentum beams. The position-dependent directionality holds true for all classical wave systems with a breathing honeycomb lattice. Our results show that a metasurfac,e in combination with a chiral two-dimensional material, could be used to guide light effectively on the nanoscale.</jats:p>
Galiffi E, Wang Y-T, Lim Z, et al., 2020, Wood Anomalies and Surface-Wave Excitation with a Time Grating, Physical Review Letters, Vol: 125, ISSN: 0031-9007
Yang F, Huidobro PA, Pendry JB, 2020, Electron Energy Loss Spectroscopy of Singular Plasmonic Metasurfaces, LASER & PHOTONICS REVIEWS, Vol: 14, ISSN: 1863-8880
Proctor M, Huidobro PA, Maier SA, et al., 2020, Manipulating topological valley modes in plasmonic metasurfaces, Nanophotonics, Vol: 9, Pages: 657-665, ISSN: 2192-8606
The coupled light-matter modes supported by plasmonic metasurfaces can be combined with topological principles to yield subwavelength topological valley states of light. We give a systematic presentation of the topological valley states available for lattices of metallic nanoparticles: All possible lattices with hexagonal symmetry are considered, as well as valley states emerging on a square lattice. Several unique effects which have yet to be explored in plasmonics are identified, such as robust guiding, filtering and splitting of modes, as well as dual-band effects. We demonstrate these by means of scattering computations based on the coupled dipole method that encompass the full electromagnetic interactions between nanoparticles.
Yang F, Galiffi E, Huidobro PA, et al., 2020, Nonlocal effects in plasmonic metasurfaces with almost touching surfaces, PHYSICAL REVIEW B, Vol: 101, ISSN: 2469-9950
Galiffi E, Arroyo Huidobro P, Pendry J, et al., Probing Graphene's nonlocality with singular metasurfaces, Nanophotonics, ISSN: 2192-8606
: Singular graphene metasurfaces, conductivity gratings realized by periodically suppressing the local dopinglevel of a graphene sheet, have recently been proposed to efficiently harvest THz light and couple it to surface plasmonsover broad absorption bands, achieving remarkably highfield enhancement. However, the large momentum wavevectors thus attained are sensitive to the nonlocal behaviourof the underlying electron liquid. Here, we extend the theory of singular graphene metasurfaces to account for thefull nonlocal optical response of graphene and discuss theresulting impact on the plasmon resonance spectrum. Finally, we propose a simple local analogue model that isable to reproduce the effect of nonlocality in local-responsecalculations by introducing a constant conductivity offset,which could prove a valuable tool in the modelling of morecomplex experimental graphene-based platforms.
Proctor M, Craster RV, Maier SA, et al., 2019, Exciting Pseudospin-Dependent Edge States in Plasmonic Metasurfaces, ACS PHOTONICS, Vol: 6, Pages: 2985-2995, ISSN: 2330-4022
Galiffi E, Huidobro PA, Goncalves PAD, et al., 2019, Probing graphene's nonlocality with singular metasurfaces, Publisher: arXiv
Singular graphene metasurfaces, conductivity gratings realized by periodically suppressing the local doping level of a graphene sheet, have recently been proposed to efficiently harvest THz light and couple it to surface plasmons over broad absorption bands, achieving remarkably high field enhancement. However, the large momentum wavevectors thus attained are sensitive to the nonlocal behaviour of the underlying electron liquid. Here, we extend the theory of singular graphene metasurfaces to account for the full nonlocal optical response of graphene and discuss the resulting impact on the plasmon resonance spectrum. Finally, we propose a simple local analogue model that is able to reproduce the effect of nonlocality in local-response calculations by introducing a constant conductivity offset, which could prove a valuable tool in the modelling of more complex experimental graphene-based platforms.
Huidobro PA, Galiffi E, Guenneau S, et al., 2019, Fresnel drag in space-time-modulated metamaterials, Publisher: arXiv
A moving medium drags light along with it as measured by Fizeau and explained by Einstein's theory of special relativity. Here we show that the same effect can be obtained in a situation where there is no physical motion of the medium. Modulations of both the permittivity and permeability, phased in space and time in the form of travelling waves, are the basis of our model. Space-time metamaterials are represented by effective bianisotropic parameters, which can in turn be mapped to a moving homogeneous medium. Hence these metamaterials mimic a relativistic effect without the need for any actual material motion. We discuss how both the permittivity and permeability need to be modulated in order to achieve these effects, and we present an equivalent transmission line model.
Pocock S, Huidobro PA, Giannini V, 2019, Bulk-edge correspondence and long range hopping in the topological plasmonic chain, Nanophotonics, Vol: 8, Pages: 1337-1347, ISSN: 2192-8606
The existence of topologically protected edge modes is often cited as a highly desirable trait of topological insulators. However, these edge states are not always present. A realistic physical treatment of long-range hopping in a one-dimensional dipolar system can break the symmetry that protects the edge modes without affecting the bulk topological number, leading to a breakdown in bulk-edge correspondence (BEC). Hence, it is important to gain a better understanding of where and how this occurs, as well as how to measure it. Here we examine the behaviour of the bulk and edge modes in a dimerised chain of metallic nanoparticles and in a simpler non-Hermitian next-nearest-neighbour model to provide some insights into the phenomena of bulk-edge breakdown. We construct BEC phase diagrams for the simpler case and use these ideas to devise a measure of symmetry-breaking for the plasmonic system based on its bulk properties. This provides a parameter regime in which BEC is preserved in the topological plasmonic chain, as well as a framework for assessing this phenomenon in other systems.
Galiffi E, Huidobro PA, Pendry JB, 2019, Broadband nonreciprocal THz amplification in luminal graphene metasurfaces, Publisher: arXiv
Time has emerged as a new degree of freedom for metamaterials, promising newpathways in wave control. However, electromagnetism suffers from limitations inthe modulation speed of material parameters. Here we argue that theselimitations can be circumvented by introducing a traveling-wave refractiveindex modulation, with the same phase velocity of the waves. We show how theconcept of "luminal grating" can yield giant nonreciprocity, achieve efficientone-way amplification, pulse compression and frequency up-conversion, proposinga realistic implementation in double-layer graphene.
Guerra Hernandez LA, Huidobro PA, Cortes E, et al., 2019, Resonant Far- to Near-Field Channeling in Synergetic Multiscale Antennas, ACS PHOTONICS, Vol: 6, Pages: 1466-1473, ISSN: 2330-4022
Yang F, Wang Y-T, Huidobro PA, et al., 2019, Nonlocal effects in singular plasmonic metasurfaces, Physical Review B, Vol: 99, ISSN: 2469-9950
A local model of the dielectric response of a metal predicts that singular surfaces, such as sharp-edged structures, have a continuous absorption spectrum and extreme concentration of energy at the singularity. Here, we show that nonlocality drastically alters this picture: The spectrum is now discrete and the energy concentration, though still substantial, is greatly reduced.
Rider MS, Palmer SJ, Pocock SR, et al., 2019, A perspective on topological nanophotonics: current status and future challenges, Journal of Applied Physics, Vol: 125, ISSN: 0021-8979
Topological photonic systems, with their ability to host states protectedagainst disorder and perturbation, allow us to do with photons what topological insulators do with electrons. Topological photonics can refer to electronic systems coupled with light or purely photonic setups. By shrinking these systems to the nanoscale, we can harness the enhanced sensitivity observed in nanoscale structures and combine this with the protection of the topological photonic states, allowing us to design photonic local density of states and to push towards one of the ultimate goals of modern science: the precise control of photons at the nanoscale. This is paramount for both nano-technological applications and also for fundamental research in light matter problems. For purely photonic systems, we work with bosonic rather than fermionic states, so the implementation of topology in these systems requires new paradigms. Trying to face these challenges has helped in the creation of the exciting new field of topological nanophotonics, with far-reaching applications. In this prospective article we review milestones in topological photonics and discuss how they can be built upon at the nanoscale.
Galiffi E, Pendry J, Arroyo Huidobro P, 2019, Singular Graphene Metasurfaces, EPJ Applied Metamaterials, Vol: 6, ISSN: 2272-2394
The spatial tunability of the electron density in graphene enables the dynamic engineering of metasurfaces in the form of conductivity gratings, which can bridge the momentum gap between incident radiation and surface plasmons. Here, we discuss singular graphene metasurfaces, whose conductivity is strongly suppressed at the grating valleys. By analytically characterising their plasmonic response via transformation optics, we first review the physical principles underlying these structures, which were recently found to exhibit broadband, tunable THz absorption. We characterise the spectrum with different common substrates and then move to study in further detail how conductivity gratings may be finely tuned by placing an array of charged gold nanowires at sub-micron distance from the graphene.
Pendry JB, Huidobro PA, Ding K, 2019, Computing one-dimensional metasurfaces, Physical Review B, Vol: 99, ISSN: 2469-9950
We show that complex periodic metasurfaces can be simply represented by conformal transformations from the flat surface of a slab of material to a periodic grating leading to a methodology for computing their properties. Matrix equations are solved to give accurate solutions of Maxwell's equations with detailed derivations given in the Supplemental Material.
Yang F, Huidobro PA, Pendry JB, 2018, Transformation optics approach to singular metasurfaces, Physical Review B, Vol: 98, ISSN: 2469-9950
Surface plasmons dominate the optical response of metal surfaces, and their nature is controlled by surface geometry. Here we study metasurfaces containing singularities in the form of sharp edges and characterized by three quantum numbers despite the two-dimensional nature of the surface. We explore the nature of the plasmonic excitations, their ability to generate large concentrations of optical energy, and the transition from the discrete excitation spectrum of a nonsingular surface to the continuous spectrum of a singular metasurface.
Pocock SR, Xiao X, Huidobro PA, et al., 2018, The topological plasmonic chain with retardation and radiative effects, ACS Photonics, Vol: 5, Pages: 2271-2279, ISSN: 2330-4022
We study a one-dimensional plasmonic system with nontrivial topology: a chain of metallic nanoparticles with alternating spacing, which in the limit of small particles is the plasmonic analogue to the Su-Schrieffer-Heeger model. Unlike prior studies we take into account long-range hopping with retardation and radiative damping, which is necessary for the scales commonly used in plasmonics experiments. This leads to a non-Hermitian Hamiltonian with frequency dependence that is notably not a perturbation of the quasistatic model. We show that the resulting band structures are significantly different, but that topological features such as quantized Zak phase and protected edge modes persist because the system has the same eigenmodes as a chirally symmetric system. We discover the existence of retardation-induced topological phase transitions, which are not predicted in the SSH model. We find parameters that lead to protected edge modes and confirm that they are highly robust under disorder, opening up the possibility of protected hotspots at topological interfaces that could have novel applications in nanophotonics.
Galiffi E, Pendry JB, Huidobro PA, 2018, Broadband tunable THz absorption with singular graphene metasurfaces, ACS Nano, Vol: 12, Pages: 1006-1013, ISSN: 1936-0851
By exploiting singular spatial modulations of the graphene conductivity, we design a broadband, tunable THz absorber whose efficiency approaches the theoretical upper bound for a wide absorption band with a fractional bandwidth of 185%. Strong field enhancement is exhibited by the modes of this extended structure, which is able to excite a wealth of high-order surface plasmons, enabling deeply subwavelength focusing of incident THz radiation. Previous studies have shown that the conductivity can be modulated at GHz frequencies, which might lead to the development of efficient high-speed broadband switching by an atomically thin layer.
Pendry JB, Huidobro PA, Luo Y, et al., 2017, Compacted dimensions and singular plasmonic surfaces, Science, Vol: 358, Pages: 915-917, ISSN: 0036-8075
In advanced field theories, there can be more than four dimensions to space, the excess dimensions described as compacted and unobservable on everyday length scales. We report a simple model, unconnected to field theory, for a compacted dimension realized in a metallic metasurface periodically structured in the form of a grating comprising a series of singularities. An extra dimension of the grating is hidden, and the surface plasmon excitations, though localized at the surface, are characterized by three wave vectors rather than the two of typical two-dimensional metal grating. We propose an experimental realization in a doped graphene layer.
Ma Z, Hanham SM, Huidobro PA, et al., 2017, Terahertz particle-in-liquid sensing with spoof surface plasmon polariton waveguides, APL Photonics, Vol: 2, ISSN: 2378-0967
We present a highly sensitive microfluidic sensing technique for the terahertz (THz) region of the electromagnetic spectrum based on spoof surface plasmon polaritons (SPPs). By integrating a microfluidic channel in a spoof SPP waveguide, we take advantage of these highly confined electromagnetic modes to create a platform for dielectric sensing of liquids. Our design consists of a domino waveguide, that is, a series of periodically arranged rectangular metal blocks on top of a metal surface that supports the propagation of spoof SPPs. Through numerical simulations, we demonstrate that the transmission of spoof SPPs along the waveguide is extremely sensitive to the refractive index of a liquid flowing through a microfluidic channel crossing the waveguide to give an interaction volume on the nanoliter scale. Furthermore, by taking advantage of the insensitivity of the domino waveguide’s fundamental spoof SPP mode to the lateral width of the metal blocks, we design a tapered waveguide able to achieve further confinement of the electromagnetic field. Using this approach, we demonstrate the highly sensitive detection of individual subwavelength micro-particles flowing in the liquid. These results are promising for the creation of spoof SPP based THz lab-on-a-chip microfluidic devices that are suitable for the analysis of biological liquids such as proteins and circulating tumour cells in buffer solution.
Pocock SR, Huidobro PA, Giannini V, 2017, The effects of retardation on the topological plasmonic chain: plasmonic edge states beyond the quasistatic limit, Publisher: arXiv
We study a one-dimensional plasmonic system with non-trivial topology: achain of metallic nanoparticles with alternating spacing, which is theplasmonic analogue to the Su-Schreiffer-Heeger model. We extend previousefforts by including long range hopping with retardation and radiative damping,which leads to a non-Hermitian Hamiltonian with frequency dependence. Wecalculate band structures numerically and show that topological features suchas quantised Zak phase persist due to chiral symmetry. This predicts parametersleading to topologically protected edge modes, which allows for positioning ofdisorder-robust hotspots at topological interfaces, opening up novelnanophotonics applications.
Siroki G, Huidobro PA, Giannini V, 2017, Topological photonics: From crystals to particles, PHYSICAL REVIEW B, Vol: 96, ISSN: 2469-9950
Arroyo-Huidobro P, Maier SA, Pendry, 2017, Tunable plasmonic metasurface for perfect absorption, EPJ Applied Metamaterials, Vol: 4, ISSN: 2272-2394
Tunable metasurfaces, whose functionality can be dynamically modified, open up the possibil-ity of ultra-compact photonic components with reconfigurable applications. Here we consider agraphene monolayer subject to a spatially periodic gate bias, which, thank to surface plasmons inthe graphene, acts as a tunable and extremely compact metasurface for terahertz radiation. Aftercharacterizing its functionality, we show that it serves as the basic building block of an ultrathincomplete absorber. In this subwavelength-thickness device, transmission and reflection channels areblocked and electromagnetic energy is completely absorbed by the metasurface building blocks. Theproposed structure can be used as a modulator, and its frequency of operation can be changed byscaling its size or adjusting the doping level.
Cortés E, Huidobro PA, Sinclair HG, et al., 2016, Plasmonic nanoprobes for stimulated emission depletion nanoscopy, ACS Nano, Vol: 10, Pages: 10454-10461, ISSN: 1936-0851
Plasmonic nanoparticles influence the absorption and emission processes of nearby emitters due to local enhancements of the illuminating radiation and the photonic density of states. Here, we use the plasmon resonance of metal nanoparticles in order to enhance the stimulated depletion of excited molecules for super-resolved nanoscopy. We demonstrate stimulated emission depletion (STED) nanoscopy with gold nanorods with a long axis of only 26 nm and a width of 8 nm. These particles provide an enhancement of up to 50% of the resolution compared to fluorescent-only probes without plasmonic components irradiated with the same depletion power. The nanoparticle-assisted STED probes reported here represent a ∼2 × 103 reduction in probe volume compared to previously used nanoparticles. Finally, we demonstrate their application toward plasmon-assisted STED cellular imaging at low-depletion powers, and we also discuss their current limitations.
Huidobro PA, Kraft M, Maier SA, et al., 2016, Graphene as a Tunable Anisotropic or IsotropicPlasmonic Metasurface, ACS Nano, Vol: 10, Pages: 5499-5506, ISSN: 1936-086X
We demonstrate a tunable plasmonic metasurface by considering a graphene sheetsubject to a periodically patterned doping level. The unique optical properties ofgraphene result in electrically tunable plasmons that allow for extreme confinementof electromagnetic energy in the technologically significant regime of THz frequencies.Here we add an extra degree of freedom by using graphene as a metasurface, proposingto dope it with an electrical gate patterned in the micron or sub-micron scale. Byextracting the effective conductivity of the sheet we characterize metasurfaces periodicallymodulated along one or two directions. In the first case, and making use of theanalytical insight provided by transformation optics, we show an efficient control ofTHz radiation for one polarization. In the second case, we demonstrate a metasurfacewith an isotropic response that is independent of wave polarization and orientation.
Here we study subwavelength gratings for coupling into graphene plasmons by means of an an-alytical model based on transformation optics that is not limited to very shallow gratings. Weconsider gratings that consist of a periodic modulation of the charge density in the graphene sheet,and gratings formed by this conductivity modulation together with a dielectric grating placed inclose vicinity of the graphene. Explicit expressions for the dispersion relation of the plasmon po-laritons supported by the system, and reectance and transmittance under plane wave illuminationare given. We discuss the conditions for maximising the coupling between incident radiation andplasmons in the graphene, finding the optimal modulation strength for a conductivity grating.
Huidobro PA, Moreno E, Martin-Moreno L, et al., 2015, Magnetic Localized Surface Plasmons Supported by Metal Structures, 9th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics (METAMATERIALS), Publisher: IEEE, Pages: 13-15
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