Plasmon-like Modes Research Articles

High-Q Tamm plasmon-like resonance in spherical Bragg microcavity resonators.

This work proposes what we believe to be a novel Tamm plasmon-like resonance supporting structure consisting of an Au/SiO2 core-shell metal nanosphere structure surrounded by a TiO2/SiO2 spherical Bragg resonator (SBR). The cavity formed between the core metal particle and the SBR supports a localized mode similar to Tamm plasmons in planar dielectric multilayers. Theoretical simulations reveal a sharp absorption peak in the SBR bandgap region, associated with this mode, together with strong local field enhancement. We studied the modification of a dipolar electric emitter's radiative and non-radiative decay rates in this resonant structure, resulting in a quantum efficiency of ∼90% for a dipole at a distance of r=60n m from the Au nanosphere surface. A 30-layer metal-SBR Tamm plasmon-like resonant supporting structure results in a Q up to ∼103. The Tamm plasmon-like mode is affected by the Bragg wavelength and the number of layers of the SBR, and the thickness of the spacer cavity layer. These results will open a new avenue for generating high-Q Tamm plasmon-like modes for switches, optical logic computing devices, and nonlinear applications.

Coupled plasmon-LO-phonon modes in the ground state of a GaAs-based electron-electron biwire system

We study the coupled plasmon-longitudinal optical-phonon (pl-LO-ph) modes in a GaAs-based electron-electron (e-e) biwire system at absolute zero within the dynamic mean-field approximation of Singwi and others (popularly known as the qSTLS theory). Here, in addition to the standard electron-electron (e-e) interactions, we also take into account the electron-phonon (e-ph) coupling and calculate pl-LO-ph modes at some selected values of wire-width, inter-wire separation and electron number density. The coupled modes are found to resonantly split into eight branches, four of which lie outside and four inside the electron-hole (e-h) pair continuum. Out of four branches which exist above the e-h pair continuum, two are plasmon-like modes having energies below than that of transverse optical (TO) phonons, and the other two are phonon-like modes having energies above longitudinal optical (LO) phonons. Additionally, we compare the plasmon-like modes with true plasmons (resulting only from the typical e-e interactions) and note that the e-ph coupling softens the true plasmon modes.

Collective modes of polarizable holographic media in magnetic fields

We consider a neutral holographic plasma with dynamical electromagnetic interactions in a finite external magnetic field. The Coulomb interactions are introduced via mixed boundary conditions for the Maxwell gauge field. The collective modes at finite wave-vector are analyzed in detail and compared to the magneto-hydrodynamics results valid only at small magnetic fields. Surprisingly, at large magnetic field, we observe the appearance of two plasmon-like modes whose corresponding effective plasma frequency grows with the magnetic field and is not supported by any background charge density. Finally, we identify a mode collision which allows us to study the radius of convergence of the linearized hydrodynamics expansion as a function of the external magnetic field. We find that the radius of convergence in momentum space, related to the diffusive transverse electromagnetic mode, increases quadratically with the strength of the magnetic field.

Beating pattern in radiation-induced oscillatory magnetoresistance in 2DES: Coupling of plasmon-like and acoustic phonon modes

We present a microscopic theory on the observation of a beating pattern in the radiation-induced magnetoresistance oscillations at a very low magnetic field. We consider that such a beating pattern develops as a result of the coupling between two oscillatory components: the first is a system of electron Landau states being harmonically driven by radiation. The second is a lattice oscillation, i.e., an acoustic phonon mode. We analyze the dependence of the beating pattern on temperature, radiation frequency, and power. We conclude that the beating pattern is an evidence of the radiation-driven nature of the irradiated Landau states that makes them behave as a collective plasma oscillation at the radiation frequency. Thus, the frequency of such plasmons could be tuned from microwave to terahertz in the same nanodevice with an apparent technological application.

Non-Equilibrium Thermodynamics Approach for QED Heat Conductance Between Graphene and SiC Substrate

Our study aims to explore heat transfer mechanism between graphene and polar insulator substrate. We develop a thermodynamic theory of heat transfer between graphene and SiC substrate based on master equation method and establish the difference of our model to the results obtain earlier by Fischetti (Ref.[1]), their equilibrium theory will be compared with the steady state solution of our non-eqilibrium model. Graphene has attracted much attention due to potential applications in thermoelectric and photoelectric devices. Thermal properties of graphene have been extensively studied both experimentally and theoretically: graphene has very high in-plane thermal conductivity. Thus the thermal applications might be likely limited by the out-of-plane heat transfer [2]. In this context, integration of graphene with a polar substrate, such as SiC, can modify the thermal properties of former [3]. In this paper, we consider strong coupling between the surface plasmon- and phonon-polaritons in graphene and the substrate, respectively. These modes were assumed to provide the efficient QED heat flux channels. Fig.1 (a) shows dispersion relations of two (infinite lifetime) eigenstates E1and E2strongly mixed due to the quasi-electrostatic interaction between surface plasmon- and phonon-polaritons. Such localized surface modes are, in fact, dissipated into reservoir modes representing the bulk of materials, which can be calculated via the corresponding self-energy terms. This interaction between surface modes and their couterparts in the reservoirs (environmental modes) leads to the loss of the quantum coherence and the dissipation of their energy, when driven out of their equilibrium (with the reservoirs). Assuming weak system-reservoir interactions and a short reservoir correlation time, Markovian quantum master equations can be used to describe relaxation dynamics of our system. Time evolution of the system was theoretically obtained. Assuming different temperatures for substrate and graphene, the coupled system is out of equilibrium which creates an non-zero net heat flux. The dynamics of the system towards the steady state can simulated. The average occupation shows an oscillatory behavior (Fig.1 d and e), here we consider the substrate being at a higher temperature. The heat flow from the surface optical phonon-like modes to graphene and from the substrate into the surface plasmon-like modes are shown in Fig.1b and c. In the steady state (long-time limit), the solution of our model does not coincide with thermal equilibrium state. This work is supported by AFOSR (#FA9550-11-1-0185). [1] Z. Y. Ong and Massimo V. Fischetti, Phys. Rev. B 86, 165422 (2011) [2] A. A. Balandin, S. Ghosh, W. Z. Bao, I. Calizo, D. Teweldebrhan, F. Miao, and C. N. Lau, Nano Lett. 8, 902 (2008) [3] J. H. Seol, I. Jo, A. L. Moore, L. Lindsay, Z. H. Aitken, M. T. Pettes, X. Li, Z. Yao, R. Huang, D. Broido, N. Mingo, R. S. Ruoff, and L. Shi, Science 328, 213 (2010). Figure 1

Review of mid-infrared plasmonic materials

The field of plasmonics has the potential to enable unique applications in the mid-infrared (IR) wavelength range. However, as is the case regardless of wavelength, the choice of plasmonic material has significant implications for the ultimate utility of any plasmonic device or structure. In this manuscript, we review the wide range of available plasmonic and phononic materials for mid-IR wavelengths, looking in particular at transition metal nitrides, transparent conducting oxides, silicides, doped semiconductors, and even newer plasmonic materials such as graphene. We also include in our survey materials with strong mid-IR phonon resonances, such as GaN, GaP, SiC, and the perovskite SrTiO3, all of which can support plasmon-like modes over limited wavelength ranges. We will discuss the suitability of each of these plasmonic and phononic materials, as well as the more traditional noble metals for a range of structures and applications and will discuss the potential and limitations of alternative plasmonic materials at these IR wavelengths.

Multiband localized spoof plasmons in closed textured cavities.

In this work, we explore the existence of multiband localized spoof plasmons (LSPs) in closed textured cavities with multiple groove depths. It is interesting to note that the spoof LSPs in each band resemble those generated by the textured 2D cavities of the same periodicity with the corresponding single groove depth, and the field distributions and confinement characteristics of the plasmon-like modes in such a corrugated cavity are different from the conventional cavity. Hence, these multiple resonance band structures can find potential applications in the microwave and terahertz frequencies.

Observation of resonant states in negative refractive photonic crystals

In this paper, experimental evidences about the resonance phenomena in a negative 2D photonic crystal are shown. Localized plasmon-like modes and guided mode resonances are detected in the reflectivity spectrum of a photonic crystal slab irradiated with out-of-plane incident radiation. The strong confinement of the radiation, in addition to the field enhancement, make photonic crystals a very appealing alternative to plasmonic substrates, avoiding the limits of absorption losses in metals.

Plasmon-like surface states in negative refractive index photonic crystals

In this paper, the presence of localized plasmon-like modes at the surface of a silicon two-dimensional photonic crystal slab is demonstrated. In analogy with surface plasmons supported in metals, we observe that, in a photonic crystal metamaterial, the electromagnetic surface waves arise from a negative effective permittivity. The proposed device is dimensioned in order to support surface states in a large spectral window (≃1550–1650 nm). The result opens strategies in light control at the nanoscale, allowing on chip light manipulation in a wide frequency range and avoiding the intrinsic limits of plasmonic structures due to absorption losses in metals.

Surface-plasmon-like modes of graphite powder compact in microwave heating

We determine the mechanism of rapid and selective heating of nonmagnetic conductive particles by the electric and magnetic fields of microwaves. We investigated the dependencies of the heating behaviors of carbon powders on the radius and electrical conductivity for various relative densities. In these experiments, strong microwave absorption was observed in magnetic field at certain radii and ratios of the crystallite size to the radius. Mie theory for a single particle could account for the high heating rates generated by the microwave magnetic field in sintering experiments. In the dependence of the heating behavior on the relative density, that H field exhibited the maximum absorption at certain relative densities of the graphite powders. These surface plasmon-like modes were observed in graphite, but were not observed when an E field was applied. Multiparticle systems such as graphite powder were found to have significantly different heating behaviors from a single particle. Microwave heating of metal particles is expected to be affected by the structure and shape of the particles.

Confined plasmonic modes in a nanocavity

The effect of confinement on surface plasmon polariton in a planar nanocavity was studied. The generalized modes were obtained and studied in detail. It was demonstrated that these modes result from the strong coupling of plasmon-like and photon-like modes.

Structurally dictated anisotropic “designer surface plasmons”

The concept of pseudo-plasmonic surfaces at microwave frequencies is extended to include structures with a high degree of surface anisotropy. The experimental sample is fabricated by patterning a metal with a rectangular array of rectangular holes and is found to support structurally dictated surface plasmon-like modes; the anisotropic dispersion of which results from an ellipsoid of limiting frequencies. By exploiting the anisotropy of the unit cell, the family of higher order surface waves associated with the quantization of the electromagnetic fields within the holes is also explored.

Bloch Oscillations of Surface Plasmon-Like Modes in Waveguide Arrays That Comprise Perforated Perfect Conductor Layers and Dielectric Layers

This study investigates the optical Bloch oscillations (OBOs) in waveguide arrays that consist of alternative perfect electric conductor (PEC) layers and dielectric layers by performing both numerical simulations and theoretical analyses. In PEC dielectric waveguide arrays (PDWAs), the PEC layers are perforated with square holes to support the surface plasmon-like (SPL) modes. The relative permittivities of the dielectric layers have a constant gradient across the waveguide arrays. The OBOs in the PDWAs arise because of the excitation and coupling of the SPL modes. The ray trajectories that are predicted using Hamiltonian optics are consistent with the simulated results. When the position of incidence is fixed, the period of oscillation varies as the reciprocal of the incident frequency. However, the amplitude of oscillation is almost independent of the frequency. For a fixed incident frequency, the amplitude and period of oscillation increases and decreases, respectively as the position of incidence moves toward the dielectric layers with higher relative permittivities.

Highly Confined Hybrid Spoof Surface Plasmons in Ultrathin Metal-Dielectric Heterostructures

Highly confined "spoof" surface plasmons (SSPs) are theoretically predicted to exist in a perforated metal film coated with a thin dielectric layer. Strong modes confinement results from the additional waveguiding by the layer. Spectral characteristics, field distribution, and lifetime of these SSPs are tunable by the holes' size and shape. SSPs exist both above and below the light line, offering two classes of applications: "perfect" far-field absorption and efficient emission into guided modes. It is experimentally shown that these plasmonlike modes can turn thin, weakly absorbing semiconductor films into perfect absorbers.

Plasmon-phonon strongly coupled mode in epitaxial graphene

We report the dispersion measurements, using angle-resolved reflection electron-energy-loss spectroscopy, on two-dimensional (2D) plasmons in single and multilayer graphene which couple strongly to surface optical phonon (FK-phonon) modes of silicon carbide substrate. The coupled modes show discrete dispersion behaviors in the single and bilayer graphene. With increasing graphene layers on SiC(0001), a transition from plasmonlike dispersion to phononlike dispersion is observed. For plasmonlike modes, the dispersion is strongly damped by electron-hole pair excitations at entering single-particle continuum, while phononlike mode is undamped. In the region free of coupling, the graphene 2D plasmon exhibits acoustic behavior with linear dispersion with slope and damping determined by the Fermi-surface topology.

Impact of dynamical screening on the phonon dynamics of metallicLa2CuO4

It is shown within a quantitative calculation that poor dynamical screening of the long-ranged Coulomb interaction due to the slow charge dynamics around the $c$ axis leads in metallic ${\text{La}}_{2}{\text{CuO}}_{4}$ to low-energy electronic collective excitations in a small region around this axis, strongly mixing with certain interlayer phonons. The manifestation of such a phonon-plasmon scenario in layered systems based on a nonadiabatic charge response recently proposed on a qualitative level is quantitatively investigated by a realistic calculation of the frequency and wave-vector-dependent irreducible polarization part of the density response function. Our calculation corrects for a generic deficit of LDA calculations which as a rule predict a too large electronic $c$-axis dispersion insufficient to describe the $c$-axis charge response in general and in particular the phonons along this axis in the cuprates. As shown in this work, the latter are highly sensitive with respect to the interlayer coupling and thus a very accurate electronic dispersion along the $c$ axis is crucial. Linear response theory is used to calculate the coupled mode dispersion in the main symmetry directions of the Brillouin zone and the charge-density redistributions excited by certain strongly coupling phononlike and plasmonlike modes. The corresponding mode induced orbital averaged changes in the self-consistent potential felt by the electrons are assessed. Our analysis should be representative for the optimally to overdoped state of the cuprates where experimental evidence of a coherent three-dimensional Fermi surface and a coherent $c$-axis charge transport is given. It is demonstrated that modes from the outside of a small region around the $c$ axis can reliably be calculated within the adiabatic limit. On the other hand, modes inside this sector have to be determined nonadiabatically. In particular, the relevance of a strongly coupling nonadiabatic phononlike apex oxygen $Z$-point breathing mode ${\text{O}}_{z}^{Z}$ at about 40 meV is emphasized whose mode energy decreases with less doping.

Effect of double heterojunctions on the plasmon–phonon coupling in a GaAs/Al0.24Ga0.76As quantum well

Quasi-two-dimensional (Q2D) Coulomb interactions between plasmons and phonons in a GaAs quantum well are studied numerically. Based on the dielectric continuum model, the plasmon–confined phonon coupling and plasmon–symmetric (±) interface phonon coupling are considered. By using renormalized phonon propagators, six branches involving plasmon-like and phonon-like modes are obtained and used to study the effect on the hot-carrier average energy-loss rate (AELR). Plasmon-like modes are demonstrated to enhance the AELR around the sheet carrier density of 1011 cm−2 due to a significant contribution of the plasmon–symmetric (+) interface phonon coupled mode. The importance of interface phonon modes on the plasmon–phonon coupling (PPC) is also indicated. If the interface phonon is not considered, the AELR enhancement due to the PPC will not appear. In addition, the carrier temperature is found to be important for the AELR enhancement. As the carrier temperature is as low as possible, the AELR enhances more remarkably because the effect of reabsorption of plasmon-like modes for hot carriers (hot-plasmon effect) can be greatly suppressed.

The Role of Low-Frequency Plasmons in Molecular Adsorption: A Theoretical and Spectroscopic Study of Gold and Titanium Compounds

We explore the question of whether surface plasmons arising from metallic nanostructures can be used advantageously to affect binding interactions of adsorbed molecules, specifically, the adsorption of dihydrogen leading to enhanced binding energies under ambient conditions. To begin to address this question, we report a systematic, theoretical survey of the plasmon spectra of gold (AuLi, AuNa2, AuB2, AuAl2, AuGa2, and AuIn2) and titanium (TiB2) compounds, examining closely the low-frequency characteristics of these spectra in relation to crystal structure. First-principle calculations of the real and imaginary components of the dielectric function were performed, and the energy-loss function was derived. These calculations show that most of the compounds give rise to low-intensity, plasmon-like modes at low frequencies and can be attributed to interband transitions between states lying close to the Fermi level. We further determined experimentally whether these plasmon-like modes are excited at low frequencies from clusters of two gold compounds (AuLi and AuAl2) by measuring surface-enhancement effects in the near-infrared Raman spectrum. Strong surface-enhancement effects were indeed observed, and we report the first observation of near-infrared, surface-enhanced Raman from compounds of this kind.

Surface plasmon-like modes on structured perfectly conducting surfaces

Surface plasmon-like (SPL) modes are the electromagnetic surface eigenmodes supported by the structured perfectly conducting surfaces. The standard eigenvalue-solving method is adopted to solve these SPL modes. The field patterns of the SPL modes in the square holes for in-plane wavevectors k(x) = 2pi / 2d and k(x) = 2pi /d are TE(10)-like and TE(11), respectively. However, the field patterns can no longer be identified as any particular waveguide mode for other in-plane wavevectors. The dispersion relations of the SPL modes are obtained numerically. The change in mode character with wavevector prevents the dispersion relation from being derived by assuming only the fundamental mode in the holes. On a thin perfect conductor perforated with structures, the SPL mode splits into a high-frequency anti-symmetric mode and a low-frequency symmetric mode, which is caused by the mutual interaction of the electromagnetic evanescent fields on both sides.

Screening and Phonon-Plasmon Scenario as Calculated from a Realistic Electronic Bandstructure Based on LDA for La2CuO4

The investigations performed in this work primarily deal with the question whether or no phonon-plasmon coupling along the c-axis in metallic La 2 CuO 4 will occur in case a realistic electronic bandstructure based on the local density approximation (LDA) is employed for the calculation of the electronic polarizability II and the dielectric matrix e. Phonon-plasmon mixing will appear in a significant way if the frequency of the free, uncoupled plasmon, as determined from the zeros of the dielectric matrix e, will fall into the frequency range of the phonon modes of appropriate symmetry coupling to the plasmon. For such a possibility to arise the dispersion of the electronic bandstructure along the c-axis must be sufficiently weak (small bandwidth). Qualitatively, we recently have studied phonon-plasmon mixing by using an 11-band tight binding model for the electronic bandstructure of the CuO plane, while the electronic bandstructure along the c-axis was introduced from the outside applying suitable interlayer couplings in parametrized form. In the present calculation the electronic bandstructure employed for the calculation of n and e, respectively, results from a complete tight-binding representation of the first-principles LAPW data including La 5d, Cu 3d, 4s, 4p and O 2p states (31-band model). No additional assumptions concerning the interlayer coupling are introduced in contrast to the 11-band model. Besides the nonadiabatic regime along the Λ∼(0, 0, 1) direction where dynamical screening and phonon-plasmon mixing comes into play, the phonon dispersion is also calculated for the main symmetry directions using the adiabatic approximation, i.e. assuming static screening. Besides other features, from this calculation the growing importance of the itinerant component of the charge response in the CuO plane to achieve high-T c values can be extracted. The charge fluctuations and the self-consistent changes of the crystal potential at the ion sites as induced by the symmetrical apical oxygen breathing mode at the Z point (O Z z ), being important for nonlocal electron-phonon interaction and pair binding, are calculated for the phonon-like and plasmon-like modes. Furthermore, a comparison is made with recent inelastic neutron scattering results for certain phonon anomalies. Finally, a possible solution concerning the apparent inconsistency of the current interpretation of the neutron c-axis data with the infrared c-axis optical spectra in La 2 CuO 4 is shortly outlined. Based on this discussion, the possibility for the application of a typical (LDA) bandstructure result for the description of the c-axis response in LaCuO the other HTSCs is estimated.