Showing papers on "Dispersion relation published in 2014"
TL;DR: In this paper, a zinc-blende crystal, HgCdTe, at the point of the semiconductor-to-semimetal topological transition was studied.
Abstract: Solid-state physics and quantum electrodynamics, with its ultrarelativistic (massless) particles, meet in the electronic properties of one-dimensional carbon nanotubes, two-dimensional graphene or topological-insulator surfaces. However, clear experimental evidence for electronic states with a conical dispersion relation in all three dimensions, conceivable for certain bulk materials, is still missing. Here, we study a zinc-blende crystal, HgCdTe, at the point of the semiconductor-to-semimetal topological transition. For this compound, we observe three-dimensional massless electrons, as certified from the dynamical conductivity increasing linearly with the photon frequency, with a velocity of about 106 m s−1. Applying a magnetic field B results in a -dependence of dipole-active inter-Landau-level resonances and spin splitting of Landau levels also following a -dependence—well-established signatures of ultrarelativistic particles but until now not observed experimentally in any solid-state electronic system. Graphene and topological-insulator surfaces are well known for their two-dimensional conic electronic dispersion relation. Now three-dimensional hyperconic dispersion is shown for electrons in a HgCdTe crystal—once again bridging solid-state physics and quantum electrodynamics.
187 citations
TL;DR: In this paper, the exact form of the dispersion relation for light-cone string excitations in string theory in AdS3×S 3×T4 with mixed R-R and NS-NS 3-form fluxes was addressed.
128 citations
TL;DR: In this paper, experimental measurements of the refractive index of twelve organic solvents at five different wavelengths (450, 532, 632.8, 964 and 1,551) and a temperature of 300 K were presented.
Abstract: We report on experimental measurements of the refractive index of twelve organic solvents at five different wavelengths (450, 532, 632.8, 964 and 1,551 nm) and a temperature of 300 K. Based on these new data visible to near-infrared dispersion relations are constructed. Group-velocity dispersion (GVD) is theoretically calculated. Zero- and negative-GVD situations are identified for two common solvents in near-infrared wavelengths. Via comparison with refractive index data available in bibliography, estimated values of thermo-optic coefficients are also presented.
124 citations
TL;DR: In this paper, a traveling unidirectional localized edge states in optical honeycomb lattices are constructed analytically and conditions on whether a given pseudofield supports a traveling edge mode are discussed.
Abstract: Traveling unidirectional localized edge states in optical honeycomb lattices are analytically constructed. They are found in honeycomb arrays of helical waveguides designed to induce a periodic pseudomagnetic field varying in the direction of propagation. Conditions on whether a given pseudofield supports a traveling edge mode are discussed; a special case of the pseudofields studied agrees with recent experiments. Interesting classes of dispersion relations are obtained. Envelopes of nonlinear edge modes are described by the classical one-dimensional nonlinear Schr\"odinger equation along the edge. Nonlinear states termed edge solitons are predicted analytically and are found numerically.
121 citations
TL;DR: In this article, the dispersion characteristics of elastic waves propagating in a monolayer piezoelectric nanoplate are investigated with consideration of the surface PAs as well as the nonlocal small-scale effect.
Abstract: In this paper, the dispersion characteristics of elastic waves propagating in a monolayer piezoelectric nanoplate is investigated with consideration of the surface piezoelectricity as well as the nonlocal small-scale effect. Nonlocal electroelasticity theory is used to derive the general governing equations by introducing an intrinsic length, and the surface effects exerting on the boundary conditions of the piezoelectric nanoplate are taken into account through incorporation of the surface piezoelectricity model and the generalized Young–Laplace equations. The dispersion relations of elastic waves based on the current formulation are obtained in an explicit closed form. Numerical results show that both the nonlocal scale parameter and surface piezoelectricity have significant influence on the size-dependent properties of dispersion behaviors. It is also found that there exists an escape frequency above which the waves may not propagate in the piezoelectric plate with nanoscale thickness.
117 citations
TL;DR: In this paper, a method for the realization of gradient index devices for flexural waves in thin plates is presented based on the thickness-dependence of the dispersion relation of flexural wave, which is used to create gradient index device by means of local variations of the plate's thickness.
Abstract: This work presents a method for the realization of gradient index devices for flexural waves in thin plates. Unlike recent approaches based on phononic crystals, the present approach is based on the thickness-dependence of the dispersion relation of flexural waves, which is used to create gradient index devices by means of local variations of the plate's thickness. Numerical simulations of known circularly symmetrical gradient index lenses have been performed. These simulations have been done using the multilayer multiple scattering method and the results prove their broadband efficiency and omnidirectional properties. Finally, finite element simulations employing the full three-dimensional elasticity equations also support the validity of the designed approach.
113 citations
TL;DR: In this article, it was shown that for high plasmon momenta, the reflection phase of the plasmons in the infinite monolayer is Ω( √ 3 √ √ 6π/4 ) with respect to either chemical potential, wavelength, or dielectric substrate.
Abstract: The phase picked up by a graphene plasmon upon scattering by an abrupt edge is commonly assumed to be $\ensuremath{-}\ensuremath{\pi}$. Here, it is demonstrated that for high plasmon momenta this reflection phase is $\ensuremath{\approx}$$\ensuremath{-}3\ensuremath{\pi}/4$, virtually independent on either chemical potential, wavelength, or dielectric substrate. This nontrivial phase arises from a complex excitation of highly evanescent modes close to the edge, which are required to satisfy the continuity of electric and magnetic fields. A similar result for the reflection phase is expected for other two-dimensional systems supporting highly confined plasmons (very thin metal films, topological insulators, transition polaritonic layers, etc.). The knowledge of the reflection phase, combined with the phase picked up by the plasmon upon propagation, allows for the estimation of resonator properties from the dispersion relation of plasmons in the infinite monolayer.
111 citations
TL;DR: In this article, the relativistic chiral transport equation for massless fermions and antifermions was derived by performing a semiclassical Foldy-Wouthuysen diagonalization of the quantum Dirac Hamiltonian.
Abstract: We derive the relativistic chiral transport equation for massless fermions and antifermions by performing a semiclassical Foldy-Wouthuysen diagonalization of the quantum Dirac Hamiltonian. The Berry connection naturally emerges in the diagonalization process to modify the classical equations of motion of a fermion in an electromagnetic field. We also see that the fermion and antifermion dispersion relations are corrected at first order in the Planck constant by the Berry curvature, as previously derived by Son and Yamamoto for the particular case of vanishing temperature. Our approach does not require knowledge of the state of the system, and thus it can also be applied at high temperature. We provide support for our result by an alternative computation using an effective field theory for fermions and antifermions: the on-shell effective field theory. In this formalism, the off-shell fermionic modes are integrated out to generate an effective Lagrangian for the quasi-on-shell fermions/antifermions. The dispersion relation at leading order exactly matches the result from the semiclassical diagonalization. From the transport equation, we explicitly show how the axial and gauge anomalies are not modified at finite temperature and density despite the incorporation of the new dispersion relation into the distribution function.
110 citations
TL;DR: In this article, a unified framework for resonant absorption in periodic arrays of high index semiconductor nanowires that combines a leaky waveguide theory perspective and that of photonic crystals supporting Bloch modes, as array density transitions from sparse to dense.
Abstract: We present a unified framework for resonant absorption in periodic arrays of high index semiconductor nanowires that combines a leaky waveguide theory perspective and that of photonic crystals supporting Bloch modes, as array density transitions from sparse to dense. Full dispersion relations are calculated for each mode at varying illumination angles using the eigenvalue equation for leaky waveguide modes of an infinite dielectric cylinder. The dispersion relations along with symmetry arguments explain the selectivity of mode excitation and spectral red-shifting of absorption for illumination parallel to the nanowire axis in comparison to perpendicular illumination. Analysis of photonic crystal band dispersion for varying array density illustrates that the modes responsible for resonant nanowire absorption emerge from the leaky waveguide modes.
108 citations
TL;DR: In this article, the authors studied wave dispersion in a one-dimensional nonlinear elastic metamaterial consisting of a thin rod with periodically attached local resonators and derived an approximate dispersion relation for this system and provided an analytical prediction of band-gap characteristics.
Abstract: We study wave dispersion in a one-dimensional nonlinear elastic metamaterial consisting of a thin rod with periodically attached local resonators. Our model is based on an exact finite-strain dispersion relation for a homogeneous solid, utilized in conjunction with the standard transfer matrix method for a periodic medium. The nonlinearity considered stems from large elastic deformation in the thin rod, whereas the metamaterial behavior is associated with the dynamics of the local resonators. We derive an approximate dispersion relation for this system and provide an analytical prediction of band-gap characteristics. The results demonstrate the effect of the nonlinearity on the characteristics of the band structure, including the size, location, and character of the band gaps. For example, large deformation alone may cause a pair of isolated Bragg-scattering and local-resonance band gaps to coalesce. We show that for a wave amplitude on the order of one-eighth of the unit cell size, the effect of the nonlinearity in the structure considered is no longer negligible when the unit-cell size is one-fourteenth of the wavelength or larger.
103 citations
TL;DR: An extension of the hydrodynamic model to cope with inhomogeneous density profiles provides a relatively fast and accurate way of describing the optical response of metal surfaces at subnanometer distances.
Abstract: We use an extension of the hydrodynamic model to study nonlocal effects in the collective plasmon excitations at metal surfaces and narrow gaps between metals, including the surface spill-out of conduction band electrons. In particular, we simulate metal surfaces consisting of a smooth conduction-electron density profile and an abrupt jellium edge. We focus on aluminum and gold as prototypical examples of simple and noble metals, respectively. Our calculations agree with the dispersion relations measured from planar surfaces for these materials. Systems involving small gaps display a regime of tunnelling electrons, which is partially captured by the overlap of electron densities. This extension of the hydrodynamic model to cope with inhomogeneous density profiles provides a relatively fast and accurate way of describing the optical response of metal surfaces at subnanometer distances.
TL;DR: The theoretical framework of the general fishbone-like dispersion relation (GFLDR) is applied to cases of practical interest of shear/drift Alfven waves (SAWs/DAWs) excited by energetic particles (EPs) in toroidal fusion plasmas as mentioned in this paper.
Abstract: The theoretical framework of the general fishbone-like dispersion relation (GFLDR), presented and discussed in the Companion Paper [Phys. Plasmas 21, 072120 (2014)], is applied to cases of practical interest of shear/drift Alfven waves (SAWs/DAWs) excited by energetic particles (EPs) in toroidal fusion plasmas. These applications demonstrate that the GFLDR provides a unified approach that allows analytical and numerical calculations of stability properties, as well as mode structures and, in general, nonlinear evolutions, based on different models and with different levels of approximation. They also show the crucial importance of kinetic descriptions, accurate geometries and boundary conditions for predicting linear as well as nonlinear SAW/DAW and EP behaviors in burning plasmas. Thus, the GFLDR unified theoretical framework elevates the interpretative capability for both experimental and numerical simulation results.
TL;DR: In this paper, the authors present omnidirectional near-unity absorption of light in an ultrathin planar semiconductor layer on a metal substrate using full-field simulations and a modal analysis.
Abstract: We present omnidirectional near-unity absorption of light in an ultrathin planar semiconductor layer on a metal substrate. Using full-field simulations and a modal analysis, it is shown that more than 98% of the incident light energy can be absorbed in a mere 12 nm thick Ge layer on a Ag substrate at the wavelength of 625 nm over a wide range of angles (80% absorption up to 66° in the transverse magnetic and 67° in the transverse electric polarizations). The physical origin of such remarkable absorption properties is the coupling of incident light to the Brewster mode supported by the structure. The modal dispersion connects several critical coupling points in a dispersion diagram at which the absorption is unity and exhibits a virtually flat dispersion relation for both polarizations, resulting in omnidirectional, near-unity absorption. Potential applications of this simple, planar geometry such as photodetectors and solar cells made from various semiconductor materials are also discussed along with feas...
TL;DR: In this article, a phononic crystal (PC) composed of a square array of densely packed square iron rods in air is used to construct a near zero-refractive index (ZRI) material.
Abstract: Zero-refractive-index materials may lead to promising applications in various fields. Here, we design and fabricate a near Zero-Refractive-Index (ZRI) material using a phononic crystal (PC) composed of a square array of densely packed square iron rods in air. The dispersion relation exhibits a nearly flat band across the Brillouin zone at the reduced frequency f = 0.5443c/a, which is due to Fabry-Perot (FP) resonance. By using a retrieval method, we find that both the effective mass density and the reciprocal of the effective bulk modulus are close to zero at frequencies near the flat band. We also propose an equivalent tube network model to explain the mechanisms of the near ZRI effect. This FP-resonance-induced near ZRI material offers intriguing wave manipulation properties. We demonstrate both numerically and experimentally its ability to shield a scattering obstacle and guide acoustic waves through a bent structure.
TL;DR: In this paper, a theoretical and numerical investigation of the plasmon-induced transparency (PIT) effect in a dual-ring resonator-coupled metal-dielectric-metal waveguide system is presented.
Abstract: We report a theoretical and numerical investigation of the plasmon-induced transparency (PIT) effect in a dual-ring resonator-coupled metal–dielectric–metal waveguide system. A transfer matrix method (TMM) is introduced to analyse the transmission and dispersion properties in the transparency window. A tunable PIT is realized in a constant separation design. The phase dispersion and slow-light effect are discussed in both the resonance and non-resonance conditions. Finally, a propagation constant based on the TMM is derived for the periodic system. It is found that the group index in the transparency window of the proposed structure can be easily tuned by the period p, which provides a new understanding, and a group index ∼51 is achieved. The quality factor of resonators can also be effective in adjusting the dispersion relation. These observations could be helpful to fundamental research and applications for integrated plasmonic devices.
TL;DR: Zonca et al. as mentioned in this paper presented a unified theoretical framework for analyzing various branches of drift Alfven waves and describing their linear and nonlinear behaviors, covering a wide range of spatial and temporal scales.
Abstract: A unified theoretical framework is presented for analyzing various branches of drift Alfven waves and describing their linear and nonlinear behaviors, covering a wide range of spatial and temporal scales. Nonlinear gyrokinetic quasineutrality condition and vorticity equation, derived for drift Alfven waves excited by energetic particles in fusion plasmas, are cast in integral form, which is generally variational in the linear limit; and the corresponding gyrokinetic energy principle is obtained. Well known forms of the kinetic energy principle are readily recovered from this general formulation. Furthermore, it is possible to demonstrate that the general fishbone like dispersion relation, obtained within the present theoretical framework, provides a unified description of drift Alfven waves excited by energetic particles as either Alfven eigenmodes or energetic particle modes. The advantage of the present approach stands in its capability of extracting underlying linear and nonlinear physics as well as spatial and temporal scales of the considered fluctuation spectrum. For these reasons, this unified theoretical framework can help understanding experimental observations as well as numerical simulation and analytic results with different levels of approximation. Examples and applications are given in Paper II [F. Zonca and L. Chen, “Theory on excitations of drift Alfven waves by energetic particles. II. The general fishbone-like dispersion relation,” Phys. Plasmas 21, 072121 (2014)].
TL;DR: In this paper, the authors quantify the strength of the waves and their impact on the energy cascade in rotating turbulence by studying the wave number and frequency energy spectrum, and the time correlation functions of individual Fourier modes in numerical simulations in three dimensions in periodic boxes.
Abstract: We quantify the strength of the waves and their impact on the energy cascade in rotating turbulence by studying the wave number and frequency energy spectrum, and the time correlation functions of individual Fourier modes in numerical simulations in three dimensions in periodic boxes. From the spectrum, we find that a significant fraction of the energy is concentrated in modes with wave frequency ω ≈ 0, even when the external forcing injects no energy directly into these modes. However, for modes for which the period of the inertial waves τω is faster than the turnover time τ NL , a significant fraction of the remaining energy is concentrated in the modes that satisfy the dispersion relation of the waves. No evidence of accumulation of energy in the modes with τω=τ NL is observed, unlike what critical balance arguments predict. From the time correlation functions, we find that for modes with τω<τ sw (with τ sw the sweeping time) the dominant decorrelation time is the wave period, and that these modes also...
TL;DR: In this article, a single-photon frequency converter via a one-dimensional waveguide coupled to a three-level $V$-type atom is proposed, where an on-demand classical driving field is used to couple to the atom, allowing it to absorb a photon with a given frequency and then emit a photon of a different carried frequency.
Abstract: We propose a single-photon frequency converter via a one-dimensional waveguide coupled to a three-level $V$-type atom. An on-demand classical driving field is used to couple to the atom, allowing it to absorb a photon with a given frequency and then emit a photon with a different carried frequency. We study such a single-photon frequency conversion mechanism in two kinds of realistic physical systems: the system of coupled-resonator waveguide with cosine dispersion relation and the one of waveguide with linear dispersion relation. To demonstrate the single-photon transfer efficiency, we introduce the concept of scattering flows via the calculation of group velocities and find that the driving field prefers to be weak in the coupled-resonator waveguide but arbitrarily strong in the linear waveguide to achieve an optimal transfer efficiency. Furthermore, we demonstrate that our theoretical model is experimentally feasible with currently available technologies.
TL;DR: In this article, the authors investigated the frequency and damping rate of fast axisymmetric waves that are subject to wave leakage for a one-dimensional magnetic cylindrical structure in the solar corona.
Abstract: We investigate the frequency and damping rate of fast axisymmetric waves that are subject to wave leakage for a one-dimensional magnetic cylindrical structure in the solar corona. We consider the ideal magnetohydrodynamic (MHD) dispersion relation for axisymmetric MHD waves superimposed on a straight magnetic cylinder in the zero β limit, similar to a jet or loop in the solar corona. An analytic study accompanied by numerical calculations has been carried out to model the frequency, damping rate, and phase speed of the sausage wave around the cut-off frequency and in the long wavelength limit. Analytic expressions have been obtained based on equations around the points of interest. They are linear approximations of the dependence of the sausage frequency on the wave number around the cut-off wavelength for both leaky and non-leaky regimes and in the long wavelength limit. Moreover, an expression for the damping rate of the leaky sausage wave has been obtained both around the cut-off frequency and in the long wavelength limit. These analytic results are compared with numerical computations. The expressions show that the complex frequencies are mainly dominated by the density ratio. In addition, it is shown that the damping eventually becomes independent of the wave number in the long wavelength limit. We conclude that the sausage mode damping directly depends on the density ratios of the internal and external media where the damping declines in higher density contrasts. Even in the long wavelength limit, the sausage mode is weakly damped for high-density contrasts. As such, sausage modes could be observed for a significant number of periods in high-density contrast loops or jets.
TL;DR: Strong dispersion was found, with two nondispersive behaviors, separated by a negative density regime, and a new model, based on the coupled displacements of films, liquid channels, and gas in the foam, rationalizes all the experimental findings.
Abstract: We measured the dispersion relation for acoustic longitudinal waves in liquid foams, over a broad frequency range (60-600 kHz). Strong dispersion was found, with two non-dispersive behaviors, separated by a negative density regime. A new model, based on the coupled displacements of films, Plateau borders and gas in the foam, rationalizes all the experimental findings.
TL;DR: The dynamic structure factor in aluminum is calculated via the intermediate scattering function and the dispersion relation for the collective excitations is extracted and very good agreement is obtained for the liquid metal domain.
Abstract: We perform ab initio simulations based on finite-temperature density functional theory in order to determine the static and dynamic ion-ion structure factor in aluminum. We calculate the dynamic structure factor via the intermediate scattering function and extract the dispersion relation for the collective excitations. The results are compared with available experimental x-ray scattering data. Very good agreement is obtained for the liquid metal domain. In addition we perform simulations for warm dense aluminum in order to obtain the ion dynamics in this strongly correlated quantum regime. We determine the sound velocity for both liquid and warm dense aluminum which can be checked experimentally using narrow-bandwidth free electron laser radiation.
TL;DR: In this article, the electromagnetic properties of a waveguide loaded by complementary electric split ring resonators (CeSRRs) and the application of the waveguide in vacuum electronics were reported.
Abstract: We report the electromagnetic properties of a waveguide loaded by complementary electric split ring resonators (CeSRRs) and the application of the waveguide in vacuum electronics. The S-parameters of the CeSRRs in free space are calculated using the HFSS code and are used to retrieve the effective permittivity and permeability in an effective medium theory. The dispersion relation of a waveguide loaded with the CeSRRs is calculated by two approaches: by direct calculation with HFSS and by calculation with the effective medium theory; the results are in good agreement. An improved agreement is obtained using a fitting procedure for the permittivity tensor in the effective medium theory. The gain of a backward wave mode of the CeSRR-loaded waveguide interacting with an electron beam is calculated by two methods: by using the HFSS model and traveling wave tube theory; and by using a dispersion relation derived in the effective medium model. Results of the two methods are in very good agreement. The proposed all-metal structure may be useful in miniaturized vacuum electron devices.
TL;DR: In this article, a general dispersion relation for non-perfectly-axisymmetric annular cavities is obtained and analytically solved to provide an explicit expression for the frequencies and growth rates of all azimuthal modes of the configuration.
Abstract: Many physical problems containing rotating symmetry exhibit azimuthal waves, from electromagnetic waves in nanophotonic crystals to seismic waves in giant stars. When this symmetry is broken, clockwise (CW) and counter-clockwise (CCW) waves are split into two distinct modes which can become unstable. This paper focuses on a theoretical study of symmetry breaking in annular cavities containing a number N of flames prone to azimuthal thermo-acoustic instabilities. A general dispersion relation for non-perfectly-axisymmetric cavities is obtained and analytically solved to provide an explicit expression for the frequencies and growth rates of all azimuthal modes of the configuration. This analytical study unveils two parameters affecting the stability of the mode: (i) a coupling strength corresponding to the cumulative effects of the N flames and (ii) a splitting strength due to the symmetry breaking when the flames are different. This theory has been validated using a 3D Helmholtz solver and good agreement is found. When only two types of flames are introduced into the annular cavity, the splitting strength is found to depend on two parameters: the difference between the two burner types and the pattern used to distribute the flames along the azimuthal direction. To first order, this theory suggests that the most stable configuration is obtained for a perfectly axisymmetric configuration. Therefore, breaking the symmetry by mixing different flames cannot improve the stability of an annular combustor independently of the flame distribution pattern.
TL;DR: In this paper, the propagation characteristics of the longitudinal wave in a piezoelectric nanoplate were investigated and the dispersion relation was analyzed with different scale coefficients, wavenumbers, and voltages.
Abstract: The propagation characteristics of the longitudinal wave in a piezoelectric nanoplate were investigated in this study. The nonlocal elasticity theory was used and the surface effects were taken into account. In addition, the group velocity and phase velocity were derived and investigated, respectively. The dispersion relation was analyzed with different scale coefficients, wavenumbers, and voltages. The results showed that the dispersion degree can be strengthened by increasing the wavenumber and scale coefficient.
TL;DR: In this paper, the wave dispersion properties of KAWs and KSWs were studied in the framework of two-fluid magnetohydrodynamics and they were used to discriminate the modes responsible for kinetic-scale pressure-balanced fluctuations and turbulence in the solar wind.
Abstract: Linear properties of kinetic Alfven waves (KAWs) and kinetic slow waves (KSWs) are studied in the framework of two-fluid magnetohydrodynamics. We obtain the wave dispersion relations that are valid in a wide range of the wave frequency. and plasma-to-magnetic pressure ratio beta. The KAW frequency can reach and exceed the ion-cyclotron frequency at ion kinetic scales, whereas the KSW frequency remains sub-cyclotron. At beta similar to 1, the plasma and magnetic pressure perturbations of both modes are in anti-phase, so that there is nearly no total pressure perturbations. However, these modes also exhibit several opposite properties. At high beta, the electric polarization ratios of KAWs and KSWs are opposite at the ion gyroradius scale, where KAWs are polarized in the sense of electron gyration (right-hand polarized) and KSWs are left-hand polarized. The magnetic helicity sigma similar to 1 for KAWs and sigma similar to -1 for KSWs, and the ion Alfven ratio R-Ai > 1 for KSWs. We also found transition wavenumbers where KAWs change their polarization from left-handed to right-handed. These new properties can be used to discriminate KAWs and KSWs when interpreting kinetic-scale electromagnetic fluctuations observed in various solar-terrestrial plasmas. This concerns, in particular, identification of modes responsible for kinetic-scale pressure-balanced fluctuations and turbulence in the solar wind.
TL;DR: In this article, the effect of porous structures on reflection and dissipation of wave energy in two-layer fluid is analyzed. And the effectiveness of three types of porous structure (a semi-infinite porous structure, a finite porous structure backed by a rigid wall, and a porous structure with perforated front and rigid back walls) in reflecting and dissipating wave energy are analyzed.
Abstract: Oblique wave interaction with rectangular porous structures of various configurations in two-layer fluid are analyzed in finite water depth. Wave characteristics within the porous structure are analyzed based on plane wave approximation. Oblique wave scattering by a porous structure of finite width and wave trapping by a porous structure near a wall are studied under small amplitude wave theory. The effectiveness of three types of porous structures—a semi-infinite porous structure, a finite porous structure backed by a rigid wall, and a porous structure with perforated front and rigid back walls—in reflecting and dissipating wave energy are analyzed. The reflection and transmission coefficients for waves in surface and internal modes and the hydrodynamic forces on porous structures of the aforementioned configurations are computed for various physical parameters in two-layer fluid. The eigenfunction expansion method is used to deal with waves past the porous structure in two-layer fluid assuming the associated eigenvalues are distinct. An alternate procedure based on the Green’s function technique is highlighted to deal with cases where the roots of the dispersion relation in the porous medium coalesce. Long wave equations are derived and the dispersion relation is compared with that derived based on small amplitude wave theory. The present study will be of significant importance in the design of various types of coastal structures used in the marine environment for the reflection and dissipation of wave energy.
TL;DR: In this article, the surface effects on the dispersion characteristics of elastic waves propagating in an infinite piezoelectric nanoplate were investigated by using the surface PDE model, based on which the presence of surface stresses and surface electric displacements were taken into account in the modified mechanical and electric equilibrium relations.
Abstract: In this paper, surface effects on the dispersion characteristics of elastic waves propagating in an infinite piezoelectric nanoplate are investigated by using the surface piezoelectricity model. Based on the surface piezoelectric constitutive theory, the presence of surface stresses and surface electric displacements exerting on the boundary conditions of the piezoelectric nanoplate is taken into account in the modified mechanical and electric equilibrium relations. The partial wave technique is employed to obtain the general solutions of governing equations, and the dispersion relations with surface effects are expressed in an explicit closed form. The impacts of surface piezoelectricity, residual surface stress and plate thickness on the propagation properties of elastic waves are analyzed in detail. Numerical results show that the dispersion behaviors in piezoelectric nanoplates are size-dependent, and there exists a critical plate thickness above which the surface effects may vanish.
TL;DR: In this paper, an acoustic plasmon is predicted to occur, in addition to the conventional two-dimensional (2D) plasmons, as the collective motion of a system of two types of electronic carriers coexisting in the same 2D band of extrinsic (doped or gated) graphene.
Abstract: An acoustic plasmon is predicted to occur, in addition to the conventional two-dimensional (2D) plasmon, as the collective motion of a system of two types of electronic carriers coexisting in the same 2D band of extrinsic (doped or gated) graphene. The origin of this novel mode stems from the anisotropy present in the graphene band structure near the Dirac points K and K′. This anisotropy allows for the coexistence of carriers moving with two distinct Fermi velocities along the and directions, which leads to two modes of collective oscillation: one mode in which the two types of carriers oscillate in phase with one another (this is the conventional 2D graphene plasmon, which at long wavelengths () has the same dispersion, , as the conventional 2D plasmon of a 2D free electron gas), and the other mode found here corresponds to a low-frequency acoustic oscillation (whose energy exhibits at long-wavelengths a linear dependence on the 2D wavenumber q) in which the two types of carriers oscillate out of phase. This prediction represents a realization of acoustic plasmons originated in the collective motion of a system of two types of carriers coexisting within the same band.
01 Jan 2014
TL;DR: In this article, the authors used transformation optics (TO) to create anisotropic modulated-impedance metasurfaces able to transform planar surface waves (SW) into a predefined curved wavefront surface wave.
Abstract: Metasurfaces constitute a class of thin metamaterials, which are used from microwave to optical frequencies to create new antennas and microwave devices. This chapter describes how to use transformation optics (TO) to create anisotropic modulated-impedance metasurfaces able to transform planar surface waves (SW) into a predefined curved-wavefront surface wave. In fact, the modulated anisotropic impedance imposes a local modification of the dispersion equation and, at constant operating frequency, of the local wavevector. The general effects of metasurface modulation are similar to those obtained by TO in volumetric inhomogeneous metamaterials, namely readdressing the propagation path of an incident wave; however, significant technological simplicity is gained.
TL;DR: In this paper, the authors derived the equations of motion that govern the nonlinear evolution of the probe-pulse envelope in this scheme and found that, by properly choosing the parameters of the system, the formation and ultra-low propagation of infrared spatial solitons originate from the balance between nonlinear effects and the dispersion properties of the graphene under infrared excitation.
Abstract: Unusual dispersion relation of graphene nanoribbons for electrons can lead to an exceptionally strong optical response in the infrared regime and exhibits a very good tunable frequency. According to quantum optics and solid-material scientific principles, here we show the possibility to generate ultraslow infrared bright and dark solitons in graphene under the action of strong magnetic and infrared laser fields. By means of quantum-mechanical density-matrix formalism, we derive the equations of motion that govern the nonlinear evolution of the probe-pulse envelope in this scheme. It is found that, by properly choosing the parameters of the system, the formation and ultraslow propagation of infrared spatial solitons originate from the balance between nonlinear effects and the dispersion properties of the graphene under infrared excitation. Moreover, the unique electronic properties and selection rules near the Dirac point provide more freedom for us to study the linear and nonlinear dynamical responses of the photonics and graphene system. These results may have potential applications in telecommunication and optical information processing.