Surface Plasmon Dispersion Research Articles

Hydrodynamics of Fermi arcs: Bulk flow and surface collective modes

The hydrodynamic description of the Fermi arc surface states is proposed. In view of the strong suppression of scattering on impurities, the hydrodynamic regime for Fermi arc states should be, in principle, plausible. By using the kinetic theory, the Fermi arc hydrodynamics is derived and the corresponding effects on the bulk flow and surface collective modes are studied. For the bulk flow, the key effect of the proposed Fermi arc hydrodynamics is the modification of the corresponding boundary conditions. In a slab geometry, it is shown that, depending on the transfer rates between the surface and bulk, the hydrodynamic flow of the electron fluid inside the slab could be significantly altered and even enhanced near the surfaces. As to the spectrum of the surface collective modes, in agreement with earlier studies, it is found that the Fermi arcs allow for an additional gapless spectrum branch and a strong anisotropy of the surface plasmon dispersion relations in momentum space. The gapped modes are characterized by closed elliptic contours of constant frequency in momentum space.

Dispersion of Surface Plasmons in Structures with a Conducting Film

The dispersion equations, the group velocity, the slowdown, and the conditions for forward and backward slow and fast plasmons propagating along thin metal films, as well as along graphene sheets, including those located on a dielectric layer and in a dielectric medium, are investigated. Nondissipative and dissipative surface plasmons are considered. Backward nondissipative symmetric plasmons do not occur in a dissipative silver film. It is shown that the anomalous negative dispersion of a dissipative plasmon does not necessarily mean that this plasmon is backward. For a backward dissipative plasmon, the input impedance of the structure from the side of vacuum should be capacitive, while the plasmon itself should be incoming. Symmetric and nonsymmetric structures with these properties are considered.

Launching low-energy surface plasmons in purple gold (AuAl2)

We confirm that the unusual purple color of the intermetallic compound AuAl2 is of a plasmonic origin by launching surface plasmons (SPs) in thin AuAl2 films. We measure the SP dispersion relation and also use the films to measure the index of refraction of sucrose solutions using standard SP resonance sensing. We find that the SP energy in planar AuAl2 is approximately 2.1 eV, about 0.4 eV lower than in gold, and the material is highly resistant to oxidation. This is close to what is expected from previously reported measurements of the dielectric function of AuAl2. On this basis, we predict that AuAl2 nanoparticles will a have very strong, spectrally nearly uniform light absorbance about an order of magnitude greater than standard carbon black. Such particles may therefore find applications as obscurants or as an alternative to more complex light-absorbing gold structures in areas such as photothermal therapy or solar steam generation, or in plasmonic catalysis.

Magnetic Hyperbolic Metasurface: Concept, Design, and Applications.

A fundamental cornerstone in nanophotonics is the ability to achieve hyperbolic dispersion of surface plasmons, which shows excellent potentials in many unique applications, such as near‐field heat transport, planar hyperlens, strongly enhanced spontaneous emission, and so forth. The hyperbolic metasurfaces with such an ability, however, are currently restricted to electric hyperbolic metasurface paradigm, and realization of magnetic hyperbolic metasurfaces remains elusive despite the importance of manipulating magnetic surface plasmons (MSPs) at subwavelength scale. Here, magnetic hyperbolic metasurfaces are proposed and designed, on which diffraction‐free propagation, anomalous diffraction, negative refraction, and frequency‐dependent strong spatial distributions of the MSPs in the hyperbolic regime are experimentally observed at microwave frequencies. The findings can be applied to manipulate MSPs and design planarized devices for near‐field focusing, imaging, and spatial multiplexers. This concept is also generalizable to terahertz and optical frequencies and inspires novel quantum optical apparatuses with strong magnetic light–matter interactions.

Real-time waveform modulator based on dispersion engineering of magnetic surface plasmons

With the aim to further reduce insertion loss, we propose the design of a real-time waveform modulator by engineering the dispersion of magnetic surface plasmons (MSPs). The magnetic fields of MSPs are strongly localized, which is different from conventional electric surface plasmons (ESPs). Since there are no magnetic media in the design, the transmission loss of MSPs resulting from dielectric loss is lower than that of ESPs. Therefore, a waveform modulator with lower insertion loss can be realized. As an example, we demonstrate a real-time waveform modulator operating in the X band. Both the simulation and experiment prove that the waveform modulator is broadband and high-efficiency. The design method can also be applied to the design of a true-time delayer, a real-time Fourier transformer, a true-time compressor, and so on.

Controlling Surface Plasmon Optical Transmission by Stretching a Silver-Coated Elastomeric Grating Substrate

In this study, transmission surface plasmon resonance (TSPR) of a silver-coated elastomeric grating substrate was tuned via mechanical stretching. The wavelengths of TSPR excitation peaks, corresponding to surface plasmon dispersion modes of + 1 and − 1, were simultaneously observed. The TSPR excitation wavelength was dramatically shifted up to 80 nm when the strain of the substrate reached 13.3%. The fine control of TSPR properties of the silver-coated elastomeric grating substrate has potential applications in mechanically tunable band pass filters, optical sensors, etc.

Surface plasmon dispersion in a mid-infrared Ge/Si quantum dot photodetector coupled with a perforated gold metasurface

The photodetection improvement previously observed in mid-infrared (IR) quantum dot photodetectors (QDIPs) coupled with periodic metal metasurfaces is usually attributed to the surface light trapping and confinement due to generation of surface plasmon waves (SPWs). In the present work, a Ge/Si QDIP integrated with a metal plasmonic structure is fabricated to experimentally measure the photoresponse enhancement and verify that this enhancement is caused by the excitation of the mid-IR surface plasmons. A 50 nm-thick gold film perforated with a 1.2 μm-period two-dimensional square array of subwavelength holes is employed as a plasmonic coupler to convert the incident electromagnetic IR radiation into SPWs. Measurements of the polarization and angular dependencies of the photoresponse allow us to determine the dispersion of plasmon modes. We find that experimental dispersion relations agree well with that derived from a computer simulation for fundamental plasmon resonance, which indicates that the photodetection improvement in the mid-IR spectral region is actually caused by the excitations of surface plasmon Bloch waves.

Broadband wave plates made by plasmonic metamaterials

Although metamaterials wave-plates have been demonstrated previously, many of them suffer from the issue of narrow bandwidth since they typically rely on resonance principles and thus exhibit inevitable frequency dispersions. Here, we show that the dispersion of spoof surface plasmon (SSP) mode supported by a fishbone structure can be freely modulated by varying the structural parameters. This motivates us to establish a general strategy of building broadband wave-plates by cascading two fishbone structures with different propagation constants of SSP modes. We derive a criterion under which the cross-polarization phase-difference across the whole device can maintain at a nearly constant value over a wide frequency band, with frequency dispersions in the two fishbone structures cancelled out. As an illustration, we design and fabricate an efficient microwave quarter-wave plate and experimentally characterize its excellent polarization-control performances over a broad frequency band (7–9.2 GHz). Our findings can stimulate making dispersion-controlled high-performance optical functional devices in different frequency domains.

Spectrally resolved surface plasmon resonance dispersion using half-ball optics

In this work, a variant of a Kretschmann-type surface plasmon resonance (SPR) sensor is introduced. k-space imaging is combined with half-ball glass optics to facilitate the measurement of SPRs across the visible spectral range. In contrast to current state-of-the-art techniques, which are widely utilized in commercially available systems, the presented method allows single-shot-acquisition of the full angular reflection without any moving parts, as well as mapping of the surface plasmon dispersion by scanning across the entire visible wavelength range. Measurements on various thin metallic films demonstrate the sensitivity of the system towards minute changes of the metal surface and its close vicinity. The fast and precise measurement of surface plasmon resonances paves the way for improved detection in applications such as immunoassays or gas-sensors, especially for real-time in situ measurements.

Enhancement of light emission and internal quantum efficiency in orange and red regions for regularly arrayed InGaN/GaN nanocolumns due to surface plasmon coupling

We demonstrate enhanced light emission in the orange and red regions from regularly arrayed InGaN/GaN nanocolumns due to the surface plasmon (SP) coupling. A maximum photoluminescence (PL) enhancement ratio of 5.2 is observed by coating the nanocolumns with an Au thin film. In addition, a 2.1-fold increase in the internal quantum efficiency is obtained. Comparison of an electromagnetic field simulation and a theoretical calculation based on the SP dispersion indicates that the SP originates from a standing wave mode arising from the periodic Au/dielectric interface. The column-diameter dependence of the PL enhancement ratio can be reasonably explained by considering the simulated electric field intensity. The periodic plasmonic nanostructure is effective for improving the emission efficiencies of InGaN-based light emitters in the orange and red regions.

Giant THz surface plasmon polariton induced by high-index dielectric metasurface

We use computational approaches to explore the role of a high-refractive-index dielectric TiO2 grating with deep subwavelength thickness on InSb as a tunable coupler for THz surface plasmons. We find a series of resonances as the grating couples a normally-incident THz wave to standing surface plasmon waves on both thin and thick InSb layers. In a marked contrast with previously-explored metallic gratings, we observe the emergence of a much stronger additional resonance. The mechanism of this giant plasmonic resonance is well interpreted by the dispersion of surface plasmon excited in the air\\TiO2\\InSb trilayer system. We demonstrate that both the frequency and the intensity of the giant resonance can be tuned by varying dielectric grating parameters, providing more flexible tunability than metallic gratings. The phase and amplitude of the normally-incident THz wave are spatially modulated by the dielectric grating to optimize the surface plasmon excitation. The giant surface plasmon resonance gives rise to strong enhancement of the electric field above the grating structure, which can be useful in sensing and spectroscopy applications.

Designer surface plasmon dispersion on a one-dimensional periodic slot metasurface with glide symmetry.

In this Letter, we explore the dispersion of spoof surface plasmons supported by a single-layer glide-symmetric structure. This structure consists of an infinitely long double-notched slot perforated in a metal layer. The presence of a degeneracy of the two lowest-order modes at the Brillouin zone boundary, which have non-zero group velocity is explained and experimentally demonstrated. Further, the dependence of the band structure when glide-symmetric configuration is broken is also explored.

Dual tunable plasmon-induced transparency based on silicon-air grating coupled graphene structure in terahertz metamaterial.

A graphene plasmonic structure consists of three graphene layers mingled with a silicon-air grating is proposed. We theoretically predict and numerically simulate the plasmon-induced transparency effect in this system at terahertz wavelengths, and a dual plasmon-induced transparency peaks can be successfully tuned by virtually shifting the desired Fermi energy on graphene layers. We investigate the surface plasmon dispersion relation by means of analytic calculations, and we can achieve the numerical solution of propagation constant got by the dispersion relation. A suitable theoretical model is established to study spectral features in the plasmonic graphene system, and the theoretical results agree well with the simulations. The proposed model and findings may provide guidance for fundamental research of highly tunable optoelectronic devices.

Surface plasmon dispersion relation at an interface between thin metal film and dielectric using a quantum hydrodynamic model

The plasmon excited at the surface of a thin metal film covering on a semi-infinite dielectric substrate is investigated in detailed. The surface plasmon dispersion relation is derived and presented by using the quantum hydrodynamic theory with taking into the quantum statistical and quantum diffraction effects. The effects of the thin metal film character rs and the dielectric constant ε1 on the dispersion relations are shown and discussed, i.e., without and with quantum effects. The results show that increasing rs weakens the quantum effects while increasing ε1 can enhance the quantum effects. In addition, the plasmon dispersion relation with quantum effects is also compared to a classical model. This simple structure proposed in the paper with quantum hydrodynamic theory can be used for yielding meaningful results for studying more complex systems related to surface plasmons.

Nonlocal extensions of the electromagnetic response of plasmonic and metamaterial structures

Nonlocal effects, requiring wave-vector- $(q$-) dependent dielectric response functions, are becoming increasingly important in studies of plasmonic and metamaterial structures. The phenomenological hydrodynamic approximation is the simplest and most often used model but with limited applicability to problems involving surface plasmons. We show here that the $d$-function formalism, exact to first order in $q$, is a powerful and simple-to-use alternative, which allows for exact nonlocal extensions of local calculation schemes, e.g., finite-difference time-domain methods, without code changes. It is also extendable to order ${q}^{2}$, and we demonstrate this by comparing with various earlier ab initio calculations and experiments as well as by performing our own random-phase-approximation calculations (valid for all $q)$ of the surface-plasmon dispersions for simple metals with various electron-gas densities. Finally we show that this hydrodynamic-extended $d$-function formalism can also be applied to arbitrary plasmonic/metamaterial structures as long as the nonflat interfaces can be modeled as effective media films.

Surface plasmon dispersion in hexagonal, honeycomb and kagome plasmonic crystals.

We present a systematic experimental study on the optical properties of plasmonic crystals (PlC) with hexagonal symmetry. We compare the dispersion and avoided crossings of surface plasmon modes around the Γ-point of Au-metal hole arrays with a hexagonal, honeycomb and kagome lattice. Symmetry arguments and group theory are used to label the six modes and understand their radiative and dispersive properties. Plasmon-plasmon interaction are accurately described by a coupled mode model, that contains effective scattering amplitudes of surface plasmons on a lattice of air holes under 60°, 120°, and 180°. We determine these rates in the experiment and find that they are dominated by the hole-density and not on the complexity of the unit-cell. Our analysis shows that the observed angle-dependent scattering can be explained by a single-hole model based on electric and magnetic dipoles.

Analysis of pulse propagation through multilayer plasmonic waveguides in the quasi-bound mode region

We present a numerical analysis of surface plasmon dispersion and the nonlinear nature of wave propagation on different smooth waveguides with lossy noble metal films. We also analyze the effective parameters that can affect the dispersion behavior of a thin dielectric slab waveguide embedded in a symmetric metal film. Three kinds of metal (silver, gold, and copper) with Johnson–Christy constants have been utilized in waveguides. Four kinds of dielectric material (air, Teflon, FR-4, and silicon) have been employed in the insulator layer of the metal–insulator–metal waveguide. The dispersion curve of the metal–insulator–metal waveguide with different metal and dielectric arrangements has been studied numerically. By multi-nominal fitting of dispersion curves, we have derived the nonlinear properties of Gaussian (chirped) wave propagation, dispersion length, and pulse broadening through a three-layer plasmonic waveguide. A comparison of three-layered plasmonic waveguides with different guiding layers has been accomplished. Simulation results have shown that dispersion curves with a larger peak and a quasi-bound mode cause the Gaussian waves to be dispersed and broadened during longer traveling distances. The achieved results serve an impressive function in the design of optical switches and delay lines.

Influence of polar and metallic substrates on the surface plasmon in semi-infinite superlattice graphene structures

Abstract We investigated the role of polar and metallic substrates on the collective excitations of a semi-infinite layered graphene structures within the self-consistent field approximation. The surface plasmon dispersion in semi-infinite stack of graphene layers is indeed modified via Coulomb interaction with the metallic or polar substrate. At long wavelengths ( q→0), these new surface-polariton are situated above bulk plasmon band of the stack with an infinite number of layers, and they have a very long lifetime. However at large momentum transfer the collective surface modes being sensitive to decay into a continuum plasmon band or by emitting an electron–hole pair excitation and thus are subject to Landau damping due of the relativistic Dirac nature of charge carriers in graphene.

Plasmonic dynamic screening in a gold film by intense femtosecond laser light

It has been found experimentally that in intense femtosecond laser fields the surface plasmon dispersion has an oscillatory character as a function of the exciting laser intensity. It has been interpreted as the result of the dynamic screening of electrons by the strong laser field. A simple model is described in addition to the experimental results, being in good agreement with these findings. The results imply an electron effective mass of around 10 percent lighter than the free electron mass. The effective mass decreases with increasing laser intensity.

Surface plasmon polaritons in topological Weyl semimetals

We consider theoretically surface plasmon polaritons in Weyl semimetals. These materials contain pairs of band touching points - Weyl nodes - with a chiral topological charge, which induces an optical anisotropy and anomalous transport through the chiral anomaly. We show that these effects, which are not present in ordinary metals, have a direct fundamental manifestation in the surface plasmon dispersion. The retarded Weyl surface plasmon dispersion depends on the separation of the Weyl nodes in energy and momentum space. For Weyl semimetals with broken time-reversal symmetry, the distance between the nodes acts as an effective applied magnetic field in momentum space, and the Weyl surface plasmon polariton dispersion is strikingly similar to magnetoplasmons in ordinary metals. In particular, this implies the existence of nonreciprocal surface modes. In addition, we obtain the nonretarded Weyl magnetoplasmon modes, which acquire an additional longitudinal magnetic-field dependence. These predicted surface plasmon results are observable manifestations of the chiral anomaly in Weyl semimetals and might have technological applications.