Plasmonic States Research Articles

Plasmonically assisted channels of photoemission from metals

We analyse recently measured nonlinear photoemission spectra from Ag surfaces that reveal resonances whose energies do not scale with the applied photon energy but stay pinned to multiples of bulk plasmon energy $\hbar\omega_p$ above the Fermi level. To elucidate these unexpected and peculiar features we investigate the spectra of plasmons generated in a solid by the optically pumped electronic polarization and their effect on photoemission. By combining quadratic response formalism for calculations of photoemission yield, a nonperturbative approach to inelastic electron scattering, and first-principles calculations for the electronic structure, we demonstrate the dependence of probability amplitude for single- and multiplasmon excitations on the basic parameters characterizing the photon pulse and the system. The resulting multiexcitation spectrum evolves towards a truncated plasmonic coherent state. Analogous concept is extrapolated to interpret plasmon generation by multiphoton excited electronic polarization. Based on this we elaborate a scenario that the thus created real plasmons act as supplementary frequency-locked pump field for non-Einsteinian plasmonically assisted channels of photoemission from metals. The established paradigm enables assignment and assessment of the observed linear $\hbar\omega_p$- and nonlinear $2\hbar\omega_p$-electron yields from Ag. Such effects may be exploited for selective filtering of optical energy conversion in electronic systems.

Metallic ferromagnetic selenospinel composites of CuCr2Se4–CdCr2Se4 with double negative electromagnetic parameters

Random metamaterial with negative electric permittivity (ε < 0) and negative magnetic permeability (μ < 0) is a group of attractive alternatives to ordered double negative metamaterials (DNMs) with periodic unit cells; however, the preparation of random DNMs with a relatively convenient preparation process and their electromagnetic property adjustment are of challenge. Here, we report the preparation of metallic ferromagnetic selenospinel composites, xCdCr2Se4·(1−x)CuCr2Se4, from metallic powders by using a simple solid-state reaction process, and double negative ε and μ have been observed in the frequency range of 120–650 MHz for 0.2CdCr2Se4·0.8CuCr2Se4 and 73–520 MHz for 0.4CdCr2Se4·0.6CuCr2Se4. The negative ε is owing to the plasmonic state of delocalized carriers in the metallic ferromagnetic CuCr2Se4, which can be described with the Drude model. The suppression of the magnetic resonance induced by the eddy current has been alleviated by the proper addition of the paramagnetic semiconductor CdCr2Se4. A theoretical model deduced from Maxwell's equation has been constructed based on the skin effect to elucidate the magnetic resonance-dependent negative permeability. Our work introduces the metallic ferromagnetic chalcospinels into the field of random DNMs and sheds light on the theoretical understanding and tuning mechanism on the double negative properties.

Plasmonic anapole states of active metamolecules

Anapole states, accompanied by strong suppression of light scattering, have attracted extensive attention in recent years due to their supreme performance in enhancing both linear and nonlinear optical effects. Although both low- and high-order anapole states are observed in the dielectric particles with high refractive index, so far few studies have touched on the topic of plasmonic anapole states. Here we demonstrate theoretically and numerically that the ideal plasmonic anapole states (strong suppression of electric dipole scattering) can be achieved in metallic metamolecules via increasing the coupling strength between Cartesian electric dipole and toroidal dipole moments of the system. The increasing coupling is based on compensation of ohmic losses in a plasmon system by introducing of a gain material, the influence of which is well described by the extended coupled oscillator model. Due to suppression of dipole radiation losses, the excitation of anapole states in plasmonic systems can result in enhancement of the near fields in subwavelength spatial regions outside of nanoparticles. That is especially important for developments of nonlinear nanophotonic and plasmonic devices and active functional metamaterials, which provide facilities for strong light energy concentration at the nanoscale. Development of the considered anapole effect with increase of metamolecule components is discussed.

Photoluminescence study of SBA-15@ZnO/Au nanocomposite for potential use in Staphylococcus aureus detection

Staphylococcus aureus is most common causes of hospital-acquired infections and food-associated disease. In the last years, sensing platform based on fluorescence- nanomaterials and nanocomposites have been attracted a great attention for detection of bacteria and macromolecules. In this study, a new modified mesoporous silica SBA-15 with ZnO and Au nanoparticles (SBA-15@ZnO/Au) was prepared to enhance the photoluminescence emission of SBA-15 matrix and investigate the potential use as a nano probe for detection of S. aureus bacteria. Au nanoparticles were added to the SBA-15 after loading ZnO nanoparticles and the SBA-15@ZnO/Au nanocomposite was successfully fabricated. The Structural, morphological, physicochemical and optical properties of the prepared samples have been studied. The low-angle X-ray diffraction (XRD) pattern showed highly ordered two-dimensional hexagonal lattice of SBA-15 and the wide-angle XRD pattern proved the formation of ZnO and Au nanoparticles. The results of the Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) analysis showed that the prepared nanocomposite have a regular two dimensional hexagonal structure with cylindrical channels even after loading ZnO and Au nanoparticles. According to Nitrogen adsorption–desorption isotherm measurement, the pore diameter and the specific surface area of SBA-15@ZnO/Au nanocomposite have been obtained 3.15 nm and 604.19 m2/g. Photoluminescence (PL) spectra of bare SBA-15@ZnO/Au nanocomposite showed three peaks at central wavelength of 410, 500 and 750 nm arising from electron transfer process and radiative decay of collective plasmonic states. After addition of S. aureus bacteria, the nano probe-target complex was formed and the PL re-emission at 640 nm and quenching of PL emissions at 750 and 410 nm was observed. Furthermore, the new nanocomposite was demonstrated to have the proper sensitivity toward bacteria concentrations. The results can open promising prospect for this nanocomposite as a nano probe for detection of S. aureus in the UV–Visible region of electromagnetic spectrum.

Percolated cermets of nickel/yttrium iron garnet for double negative metacomposites

Dielectric and magnetic properties of percolative nickel/yttrium iron garnet cermets were investigated. With nickel content increasing, microstructure evolution of the cermets exhibited characteristics of percolation, resulting in electrical conductivity increased dramatically and conduction mechanism changed from hopping to metallic behaviors. Negative permittivity and negative permeability were observed. Negative permittivity was caused by the plasmonic state of delocalized electrons. Negative permeability was attributed to magnetic resonance of ferromagnetic constituents and diamagnetic responses of eddy currents induced in interconnected nickel networks. The obtained double negative metacomposites enriched metamaterials and have great potential in electromagnetic shielding, cloaking, and attenuation applications.

Tailorable negative permittivity of graphene-carbon nanotube/copper calcium titanate metacomposites

Ceramic metacomposites have been substantially investigated to obtain negative permittivity owing to their promising applications in electronics and dielectric devices. However, the modulation of negative permittivity has still been a challenging issue to be investigated. Herein, CaCu3Ti4O12 (CCTO) ceramic nanocomposites with varying content of graphene-carbon nanotube (GR-CNT) fillers were fabricated. There are two different types of radio-frequency (RF) negative permittivity in GR-CNT/CCTO metacomposites, i.e. induced dielectric resonance and plasma oscillation, which provided original envisage for tailorable negative permittivity. Resonance-type negative permittivity behavior originated from the abundant electric dipoles in the isolated GR-CNT clusters and interfacial polarization between GR-CNT and CCTO. Strongly dispersion of negative permittivity (~-104) was achieved in the metacomposites with high carbon content, which was ascribed to plasmonic state of extensive free carriers in percolating GR-CNT networks. Weakly negative permittivity (~-102) was obtained in the composites above the epsilon-near-zero frequencies, which were ~860 MHz, ~430 MHz and ~370 MHz, respectively. Inductive character of metacomposites was an intrinsic performance exactly as equivalent circuit analysis demonstrated. This work benefits for clarifying the regulation mechanism of negative permittivity, which can pave the way to expand the applications of ceramic composites in the field of metamaterials.

Wavelength-Tunable Purcell Effect in a Surface Plasmon Polariton State on a Metamaterial Edge

Layered metal-dielectric structures are easy-to-fabricate one-dimensional plasmonic metamaterials. Using the effective media approach, we consider surface plasmons that appear on an interface between such metamaterial and a dielectric. We have shown that two types of surface plasmon states appear on an interface. The frequency of the peak in the local density of states of these states is dependent on the fraction of metal in the metamaterial. By reducing the fraction, the frequency can be shifted towards longer wavelengths. There the losses of light in metal are reduced, which, as we have shown, leads to the increase in peak value of the Purcell factor.

Communication—Tunable Epsilon-Negative Property of Nickel/Copper Calcium Titanate Cermets

Nickel/copper calcium titanate (Ni/CCTO) cermets with variated Ni content were prepared. The abrupt shift of ac conductivity, reactance and complex permittivity occurred in composites. Epsilon-negative property is an intrinsically physical performance of inductive character which was explained by low-frequency plasmonic state of Ni networks. Negative value of real permittivity in metacomposites reached 109 and was tuned by adjusting the concentration of free carriers in Ni networks. The epsilon-negative materials are accompanied by strongly dielectric loss and high reactance value. This work expands the applying scope of CCTO into metacomposites and meanwhile facilitates to clarify the regulation mechanism of epsilon-negative.

Enhanced third-harmonic generation from layered graphene/insulator disks array

The non-linear responses of optical materials offer useful mechanisms for optical switching, novel optical sources, and harmonic frequency conversion. However, the non-linear response of traditional materials is usually extremely weak and requires high input power for excitation. In this study, we theoretically propose a scheme for enhancing the third harmonic generation (THG) efficiency and output power of layered graphene disks array by introducing a plasmonic antibonding state with enhanced oscillation strength due to plasmonic coupling. We verify that, the THG efficiency of a double-layer stacked graphene/SiO2 disk structure under relatively low input intensity can be significantly enhanced more than one order of magnitude with appropriate design, as compared with monolayer patterned graphene nanostructure. We also demonstrate that the THG efficiency can be further improved by optimizing the geometry parameters such as spacer distance and Fermi energy. Our results offer an effective mechanism for significantly improving THG efficiency in the mid-infrared and terahertz ranges, thereby paving the way for new frequency converters and modulators in optical communication and signal processing.

TiN/Al2O3 binary ceramics for negative permittivity metacomposites at kHz frequencies

Metacomposites with negative permittivity have attracted much attention due to their potential applications in electromagnetic shielding, novel capacitances and sensors. In this work, percolative TiN/Al2O3 ceramic composites with different TiN content were sintered and the dielectric properties were investigated from 5 kHz to 1 MHz. When the filling content of TiN increased from 20 wt% to 30 wt%, percolating phenomenon was observed and TiN grains became interconnected rather than being isolated in Al2O3 ceramic matrix. Meanwhile, electric conductivity of the ceramic composites was enhanced as TiN was incorporated and the conduction mechanism changed from hopping conduction to metal-like conduction. Compared to pure Al2O3 ceramics, the enhancement of permittivity in composites with 10 wt% and 20 wt% TiN was caused by the increased interfacial polarizations, while negative permittivity observed in composites with 30 wt% and 40 wt% TiN was attributed to the plasmonic state of electrons in percolating networks formed by TiN grains. Thus, it’s demonstrated that TiN/Al2O3 binary ceramics can be negative permittivity metacomposites. This work enriched the electromagnetic properties of TiN/Al2O3 ceramic composites.

Low-frequency plasmonic state and negative permittivity in copper/titanium dioxide percolating composites

The titanium dioxide-based varistor is generally equivalent to a combination of resistor and capacitor, whereas, for the titanium dioxide-based composite with negative permittivity, it can be composed of a resistor, capacitor, and inductor. In this work, ac conductivity, real permittivity, and reactance of copper/titanium dioxide (Cu/TiO2) percolating composites are investigated in detail in the frequency of 10 kHz - 1 MHz. As Cu content increases, percolation occurs in composites, accompanied by the transformation of electron transport mechanism from localization to delocalization. Furthermore, the regulation of permittivity by compositions and microstructures is specifically analyzed. It suggests that the enhanced permittivity before percolation ascribes to the enhancement of interfacial polarization, when reaching the excessively percolating state, plasma-like negative permittivity is achieved, consequently, revealing the low-frequency plasmonic state. Moreover, reactance analyses indicate the negative permittivity is ascribed to the inductive characteristics, and the stronger the inductance, the greater the contribution to the negative permittivity.

Dielectric dispersion of copper/rutile cermets: Dielectric resonance, relaxation, and plasma oscillation

In this work, dielectric behaviors of dielectric resonance, relaxation, and plasma-like negative permittivity are observed in percolative copper/rutile cermets. Transition for permittivity changing from positive to negative is associated with composition and determined by percolation. The resonance and relaxation responses are related to isolated metallic particles or clusters. Negative permittivity is induced by the plasmonic state of electrons within percolating pathways and dielectric loss of epsilon-negative composites is dominated by conduction loss. Besides, the percolative cermets change from electrical capacitive to inductive with the permittivity transition. Epsilon-negative cermets are expected to be used for electromagnetic shielding and coil-less electrical inductors.

Tunable plexciton dynamics in electrically biased nanojunctions

Strong coupling between resonantly coordinated plasmonic modes and excitonic states from quantum emitters or analogous two-level systems has led to the realization of pronounced plexciton dynamics. Here, we present and discuss an unconventional approach for this purpose by designing an electrically driven system composed of quantum dots (QDs) trapped in an opening region between two metallic electrodes. By conducting theoretical and numerical investigations, we quantitatively show that under specific bias, radiatively generated plasmons in the device efficiently couple to the excitonic states arisen from quantum emitters in the tunnel. This resulted in pronounced Rabi oscillations and splitting of the classical dipole mode emitted from the tunnel junctions. By computing the local density of states and electroluminescence spectra, we demonstrated the emission of light from the gated system and verified the fundamental parameters of the proposed unique architecture depending on the current flow at the barrier. By taking advantage of the local nature of the excited plasmons and varying the number of QDs in the tunnel, we precisely modeled the plexcitonic coupling and quantified the Rabi splitting of the fundamental resonances around ħΩ ≈ 200 meV. Possessing immense potential to be exploited in devising advanced technologies, we envision that the electrically driven plexciton dynamics brings on-chip ultrafast and ultradense instruments one step closer to reality.

Two-Photon Spontaneous Emission in Atomically Thin Plasmonic Nanostructures.

The ability to harness light-matter interactions at the few-photon level plays a pivotal role in quantum technologies. Single photons-the most elementary states of light-can be generated on demand in atomic and solid state emitters. Two-photon states are also key quantum assets, but achieving them in individual emitters is challenging because their generation rate is much slower than competing one-photon processes. We demonstrate that atomically thin plasmonic nanostructures can harness two-photon spontaneous emission, resulting in giant far field two-photon production, a wealth of resonant modes enabling tailored photonic and plasmonic entangled states, and plasmon-assisted single-photon creation orders of magnitude more efficient than standard one-photon emission. We unravel the two-photon spontaneous emission channels and show that their spectral line shapes emerge from an intricate interplay between Fano and Lorentzian resonances. Enhanced two-photon spontaneous emission in two-dimensional nanostructures paves the way to an alternative efficient source of light-matter entanglement for on-chip quantum information processing and free-space quantum communications.

Resonant Optical Phenomena in Heterogeneous Plasmon Nanostructures of Noble Metals: A Review

The interaction of electromagnetic radiation with ordered and disordered arrays of noble metal nanoparticles, leading to the excitation of various modes of surface plasmon states in them, is analyzed. The dipole localized surface plasmon resonance in isolated nanoparticles and the influence of various size effects on its optical response are considered. The effect of dipole-dipole interaction between gold and silver nanoparticles on the optical properties of various nanosized and nanostructured objects is discussed. It is shown that both localized and delocalized (propagated) surface plasmon modes can be excited in composite gold and silver nanosystems, in particular, in porous films. The prospects for the practical application of nanostructures with arrays of gold and silver nanoparticles in sensor technology, surface-enhanced Raman spectroscopy, and modern optoelectronics are examined.

Four-wave mixing of topological edge plasmons in graphene metasurfaces.

We study topologically protected four-wave mixing (FWM) interactions in a plasmonic metasurface consisting of a periodic array of nanoholes in a graphene sheet, which exhibits a wide topological bandgap at terahertz frequencies upon the breaking of time reversal symmetry by a static magnetic field. We demonstrate that due to the significant nonlinearity enhancement and large life time of graphene plasmons in specific configurations, a net gain of FWM interaction of plasmonic edge states located in the topological bandgap can be achieved with a pump power of less than 10 nW. In particular, we find that the effective nonlinear edge-waveguide coefficient is about γ ≃ 1.1 × 1013 W-1 m-1, i.e., more than 10 orders of magnitude larger than that of commonly used, highly nonlinear silicon photonic nanowires. These findings could pave a new way for developing ultralow-power-consumption, highly integrated, and robust active photonic systems at deep-subwavelength scale for applications in quantum communications and information processing.

Ultrahigh Brightening of Infrared PbS Quantum Dots via Collective Energy Transfer Induced by a Metal-Oxide Plasmonic Metastructure

We demonstrate that a solution-processed heterojunction interface formed via the addition of a thin buffer layer of CdSe/ZnS quantum dots (QDs) to a functional metal oxide plasmonic metastructure (FMOP) can set up a collective interquantum dot energy-transport process, significantly enhancing the emission of infrared PbS quantum dots. The FMOP includes a Schottky junction, formed via deposition of a Si layer on arrays of Au nanoantennas and a Si/Al oxide charge barrier. We show when these two junctions are separated from each other by about 15 nm and the CdSe/ZnS quantum dot buffer layer is placed in touch with the Si/Al oxide junction, the quantum efficiency of an upper layer of PbS quantum dots can increase by about 1 order of magnitude. These results highlight a unique energy circuit formed via collective coupling of the CdSe/ZnS quantum dots with the hybridized states of plasmons and diffraction modes of the arrays (surface lattice resonances) and coupling between such resonances with PbS QDs via lattice-induced photonic modes.

Communication—Tunable Epsilon-Negative Property in FeCrNi/CaCu3Ti4O12 Metacomposites

In this paper, FeCrNi/CaCu3Ti4O12 metacomposites with different FeCrNi content were fabricated by low-temperature presureless sintering process. With increasing FeCrNi content above percolation threshold, the conduction mechanism changed from hopping conduction to metal-like conduction. Meanwhile, epsilon-negative property was obtained at 70 wt%–90 wt% content of FeCrNi, ascribing to the low frequency plasmonic state from three-dimensional conductive FeCrNi networks. The correlation between epsilon-negative property and inductive character was clarified by reactance spectrum. This work benefited the exploration of metal/ceramic metacomposites which could facilitate their promising applications in invisibility, high-k capacitors, novel antennae and sensors.

Tunneling-induced negative permittivity in Ni/MnO nanocomposites by a bio-gel derived strategy

Tunneling-induced negative permittivity is attributed to the low frequency plasmonic state in tunneling networks, where nickel nanoparticles are still isolated geometrically but connected electrically.

Tunable negative permittivity behavior and electromagnetic shielding performance of silver/silicon nitride metacomposites

The recent rise of metacomposites offered a new research strategy for electromagnetic shielding materials owing to their negative electromagnetic parameters, such as negative permittivity. Herein, we prepared silver/silicon nitride (Ag/Si3N4) metacomposites with tunable negative permittivity by a facile impregnation-calcination process, and explored their electrical conductivity, permittivity and electromagnetic shielding properties. As the Ag content increased, formative metal networks in the composites rendered their conductivity characteristic changing from a hopping conductivity to a metal-like conductivity. Tunable negative permittivity behavior combined with enhanced shielding effectiveness (SE) was observed at 2–18 GHz in the metacomposites with high Ag contents. The plasma-like negative permittivity was accounted for by a low frequency plasmonic state of free electrons in the inductive Ag networks, and the frequency band and absolute magnitude of negative permittivity could be adjusted by controlling Ag content, which was well described by Drude model. The average total SE of our obtained metacomposite could reach ~30 dB, and the reflection was the primary shielding mechanism, which was attributed to the intense impedance mismatching stemmed from the negative permittivity. Our work opens up the possibility of designing metacomposites for promising electromagnetic shielding materials, promoting their application in microwave field.