Plasmon Polaritons Research Articles

Plasmon-mediated dynamics and lasing of nanoemitters enhanced by dispersing nanorings.

We investigate the plasmon-mediated nonlinear dynamics and the optics of a laser emission of random nanoemitters (NEs) embedded in a two-dimensional (2D) lattice of conducting nanorings (NRs) enhanced by plasmon-polariton (PP) excitations. The interaction of quantum NEs with the PP field in the NRs perturbs the dynamics of the electronic populations in NEs, leading to a significant dependence of laser generation (dynamics) on the plasma frequency ωp of PP. This results in a strong coupling of NE field emission with the PP field and sharp variations of the average current in the NR lattice. The phase transition in the system was found when the macroscopic structures of PP fields are excited simultaneously in different regions of the system if ωp (control parameter) reaches critical value ωc. We have established the analytical dependence of the PP current I = I(ωp/ωc) on the plasma frequency, which is in excellent agreement with the results of numerical simulations. This effect may allow the design of new types of PP active devices with the use of conducting NRs in modern nanoelectronics.

Plasmons in the Kagome metal CsV3Sb5

Plasmon polaritons, or plasmons, are coupled oscillations of electrons and electromagnetic fields that can confine the latter into deeply subwavelength scales, enabling novel polaritonic devices. While plasmons have been extensively studied in normal metals or semimetals, they remain largely unexplored in correlated materials. In this paper, we report infrared (IR) nano-imaging of thin flakes of CsV3Sb5, a prototypical layered Kagome metal. We observe propagating plasmon waves in real-space with wavelengths tunable by the flake thickness. From their frequency-momentum dispersion, we infer the out-of-plane dielectric function ϵc\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{{{{{\\boldsymbol{\\epsilon }}}}}}}_{{{{{{\\boldsymbol{c}}}}}}}$$\\end{document} that is generally difficult to obtain in conventional far-field optics, and elucidate signatures of electronic correlations when compared to density functional theory (DFT). We propose correlation effects might have switched the real part of ϵc\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{{{{{\\boldsymbol{\\epsilon }}}}}}}_{{{{{{\\boldsymbol{c}}}}}}}$$\\end{document} from negative to positive values over a wide range of middle-IR frequencies, transforming the surface plasmons into hyperbolic bulk plasmons, and have dramatically suppressed their dissipation.

Near-field detection of gate-tunable anisotropic plasmon polaritons in black phosphorus at terahertz frequencies

Polaritons in two-dimensional layered crystals offer an effective solution to confine, enhance and manipulate terahertz (THz) frequency electromagnetic waves at the nanoscale. Recently, strong THz field confinement has been achieved in a graphene-insulator-metal structure, exploiting THz plasmon polaritons (PPs) with strongly reduced wavelength (λp ≈ λ0/66) compared to the photon wavelength λ0. However, graphene PPs propagate isotropically, complicating the directional control of the THz field, which, on the contrary, can be achieved exploiting anisotropic layered crystals, such as orthorhombic black-phosphorus. Here, we detect PPs, at THz frequencies, in hBN-encapsulated black phosphorus field effect transistors through THz near-field photocurrent nanoscopy. The real-space mapping of the thermoelectrical near-field photocurrents reveals deeply sub-wavelength THz PPs (λp ≈ λ0/76), with dispersion tunable by electrostatic control of the carrier density. The in-plane anisotropy of the dielectric response results into anisotropic polariton propagation along the armchair and zigzag crystallographic axes of black-phosphorus. The achieved directional subwavelength light confinement makes this material system a versatile platform for sensing and quantum technology based on nonlinear optics.

Transient measurement of near-field thermal radiation between macroscopic objects.

The involvement of evanescent waves in the near-field regime could greatly enhance spontaneous thermal radiation, offering a unique opportunity to study nanoscale photon-phonon interaction. However, accurately characterizing this subtle phenomenon is very challenging. This paper proposes a transient all-optical method for rapidly characterizing near-field radiative heat transfer (NFRHT) between macroscopic objects, using the first law of thermodynamics. Significantly, a full measurement at a fixed gap distance is completed within tens of seconds. By simplifying the configuration, the transient all-optical method achieves high measurement accuracy and reliable reproducibility. The proposed method can effectively analyze the NFRHT in various material systems, including SiO2, SiC, and Si, which involve different phonon or plasmon polaritons. Experimental observations demonstrate significant super-Planckian radiation, which arises from the near-field coupling of bounded surface modes. Furthermore, the method achieves excellent agreement with theory, with a minimal discrepancy of less than 2.7% across a wide temperature range. This wireless method could accurately characterize the NFRHT for objects with different sizes or optical properties, enabling the exploration of both fundamental interests and practical applications.

Dispersion Engineering by Hybridizing the Back-Folded Soft Mode of Monomode Elastic Metamaterials with Stiff Acoustic Modes.

In many cases, the hybridization of two or more excitation modes in solids has led to new and useful dispersion relations of waves. Well-studied examples are phonon polaritons, plasmon polaritons, particle-plasmon polaritons, cavity polaritons, and magnetic resonances at optical frequencies. In all of these cases, the lowest propagating mode couples to a finite-frequency localized resonance. Herein, the unusual metamaterial phonon dispersion relations arising from the hybridization of an ordinary acoustical phonon mode with a back-folded soft or easy phonon mode of a monomode elastic metamaterial are discussed. Conceptually, the single easy mode can have strictly zero wave velocity. In reality, its wave velocity is very much smaller than that of all other modes. Considering polymeric three-dimensional printed elastic monomode metamaterials at ultrasound frequencies, it is shown theoretically and experimentally that the resulting pronounced avoided crossing, with a frequency splitting comparable to the mid-frequency, leads to backward-wave behavior for the lowest band over a broad frequency range, conceptually at zero loss.

Supercavity Modes Excited by Bessel‐Type Plasmon Polaritons

AbstractHigh‐index dielectric resonators are favorable to enhance light‐matter interaction with the advantages of low loss and multipolar resonances. However, realizing a high‐Q factor in a single dielectric cavity remains a challenge especially in lossy systems such as that in plasmonics. Here, the resonant modes of a dielectric cylinder excited is explored by bessel‐type plasmon polaritons and reveal the general dependence of its eigenfrequency on the physical size. Based on this fundamental a universal and robust approach is proposed to find the high‐Q supercavity modes, which arise in the vicinity of the resonance crossing features of two coupled resonant modes in the same radiation channel. Following the proposed principle, one cannot only construct a series of high‐Q modes, but also predict their corresponding size parameters and resonant frequencies without relying on the heavy computations of parameter scanning. Such high‐Q mode can be easily extended from visible wavelengths to other frequency regime due to scale invariance of the eigenfrequency and the insensitivity of the Q‐factor to the permittivity (real part) of the plasmonic substrate. The findings provide guideline for the engineering of high‐Q modes and may open up a pathway to design resonant meta‐optics devices in lossy dielectric‐metal composite system.

Ultrafast and Nanoscale Energy Transduction Mechanisms and Coupled Thermal Transport across Interfaces.

The coupled interactions among the fundamental carriers of charge, heat, and electromagnetic fields at interfaces and boundaries give rise to energetic processes that enable a wide array of technologies. The energy transduction among these coupled carriers results in thermal dissipation at these surfaces, often quantified by the thermal boundary resistance, thus driving the functionalities of the modern nanotechnologies that are continuing to provide transformational benefits in computing, communication, health care, clean energy, power recycling, sensing, and manufacturing, to name a few. It is the purpose of this Review to summarize recent works that have been reported on ultrafast and nanoscale energy transduction and heat transfer mechanisms across interfaces when different thermal carriers couple near or across interfaces. We review coupled heat transfer mechanisms at interfaces of solids, liquids, gasses, and plasmas that drive the resulting interfacial heat transfer and temperature gradients due to energy and momentum coupling among various combinations of electrons, vibrons, photons, polaritons (plasmon polaritons and phonon polaritons), and molecules. These interfacial thermal transport processes with coupled energy carriers involve relatively recent research, and thus, several opportunities exist to further develop these nascent fields, which we comment on throughout the course of this Review.

Exploring Superradiance Effects of Molecular Emitters Coupled with Cavity Photons and Plasmon Polaritons: A Perspective from Macroscopic Quantum Electrodynamics

Exploring Superradiance Effects of Molecular Emitters Coupled with Cavity Photons and Plasmon Polaritons: A Perspective from Macroscopic Quantum Electrodynamics

Theory of plasmon-polaritons in binary metallic supercrystals

We present a theory of optical excitations in binary plasmonic supercrystals that are made out of two types of metal nanoparticles. Compared to monodisperse supercrystals, binary crystals have a larger number of plasmonic bands. Their dispersion is governed by the lattice symmetry, unit cell parameters, and shape and material composition of the nanoparticle building blocks. We develop a quantum description of the plasmon polaritons in supercrystals that starts from the dipole and quadrupole excitations of the nanoparticles, their interaction, and their coupling to photons. We show how to use group theory to analyze the plasmon- and photon-induced supercrystal states and their interaction. Plasmon-polaritons of binary metallic supercrystals are in the regime of ultrastrong and deep strong light-matter interaction; i.e., the coupling strength is on the same order as the photon energy. One consequence of the strong interaction is that quadrupolar plasmon modes and photons with energies well above the plasmon energies have to be taken into account to calculate the polariton dispersion. A cesium chloride crystal of two nanoparticles with different dipole and quadrupole energies serves as the example structure to show how the plasmon-polariton dispersion depends on the properties of the nanoparticles and supercrystal structure. The tools presented here can be used to predict and analyze any type of optically active excitation in supercrystals. The results show how to differentiate the optical properties of binary nanoparticle supercrystals into properties that inflexibly depend on lattice symmetry and properties that can be finely tuned by choosing the nanoparticle composition and shape.

Modified dispersion for graphene plasmon polariton in hydrodynamic model without potential notation

A hydrodynamic model, which discards potential notation but couples with the full Maxwell's equations and boundary conditions, was proposed. The method took into account magnetic field but ascertained the type of surface plasmon-polaritons in the monolayer graphene. Utilizing the method, we investigated the spectrum of surface plasmon-polariton with or without the external magnetic field and found that the plasmon-polariton spectrum was suppressed compared with the traditional method. In the infrared and ultraviolet region, the fluence of external magnetic field can be ignored. There was an uplift in the transition region, which is roughly around q0∼1, which is attributed to the external magnetic field. Finally, the surface plasmon-polariton spectrum in the ultraviolet region was dominated by the nonlocal effect.

Real-space observation of ultraconfined in-plane anisotropic acoustic terahertz plasmon polaritons.

Thin layers of in-plane anisotropic materials can support ultraconfined polaritons, whose wavelengths depend on the propagation direction. Such polaritons hold potential for the exploration of fundamental material properties and the development of novel nanophotonic devices. However, the real-space observation of ultraconfined in-plane anisotropic plasmon polaritons (PPs)-which exist in much broader spectral ranges than phonon polaritons-has been elusive. Here we apply terahertz nanoscopy to image in-plane anisotropic low-energy PPs in monoclinic Ag2Te platelets. The hybridization of the PPs with their mirror image-by placing the platelets above a Au layer-increases the direction-dependent relative polariton propagation length and the directional polariton confinement. This allows for verifying a linear dispersion and elliptical isofrequency contour in momentum space, revealing in-plane anisotropic acoustic terahertz PPs. Our work shows high-symmetry (elliptical) polaritons on low-symmetry (monoclinic) crystals and demonstrates the use of terahertz PPs for local measurements of anisotropic charge carrier masses and damping.

Spatial shifts of reflected light beam on black phosphorus/hexagonal boron nitride structure

We examined Goos-Hänchen (GH) and Imbert-Fedorov (IF) shifts of the reflective beam from the hexagonal boron nitride (hBN) covered by black phosphorus (BP) layers, where the BP layers are rotated by an angle with respect to the incident plane. The interaction of phonon polaritons in hBN and plasmon polaritons in BP, as well as the structure surface and interface between the two media determines the two shifts. In the common frequency–response range of the BP and hBN, the GH- and IF-shifts can be very large in the vicinity of epsilon-near-zero (ENZ) for a linearly-polarized incidence. The GH-shift can be continuously tuned from positive to negative or even to zero at a fixed frequency by adjusting the electron density and anisotropic axis-orientation of the BP. Another fascinating phenomenon is that the IF-shift can be not only excited by the linearly-polarized incidence but also greatly improved, even up to -156λ0. These conclusions are applicable to the other 2D anisotropic materials, which will become a guidance of new polarization-dependent, anisotropic optoelectronics devices.

Morphology-Controlled Reststrahlen Band and Infrared Plasmon Polariton in GaN Nanostructures.

Due to ultrabright and stable blue light emission, GaN has emerged as one of the most famous semiconductors of the modern era, useful for light-emitting diodes, power electronics, and optoelectronic applications. Extending GaN's optical resonance from visible to mid- and-far-infrared spectral ranges will enable novel applications in many emerging technologies. Here we show hexagonal honeycomb-shaped GaN nanowall networks and vertically standing nanorods exhibiting morphology-dependent Reststrahlen band and plasmon polaritons that could be harnessed for infrared nanophotonics. Surface-induced dipoles at the edges and asperities in molecular beam epitaxy-deposited nanostructures lead to phonon absorption inside the Reststrahlen band, altering its shape from rectangular to right-trapezoidal. Excitation of such surface polariton modes provides a novel pathway to achieve far-infrared optical resonance in GaN. Additionally, surface defects in nanostructures lead to high carrier concentrations, resulting in tunable mid-infrared plasmon polaritons with high-quality factors. Demonstration of morphology-controlled Reststrahlen band and plasmon polaritons make GaN nanostructures attractive for infrared nanophotonics.

Axion-plasmon-polariton hybridization in a graphene periodic structure

This study investigated the hybridization between an axion and plasmon polariton, attributed to the coupling achieved by combining modified electrodynamics and hydrodynamic approaches on a plasmon-polariton in a graphene periodic structure. The enhancement of the effective coupling was also studied. Furthermore, corrections for the axion and the lowest plasmon -polariton hybridization state spectra have been presented. An observable was proposed to detect axions, which is significant even when the effective coupling is not large, especially as the axion mass decreases. The study shows that the resulting structure provides a sensitive and wide-mass-spectrum platform for detecting axions at the sub-meV scale.

Polarization properties in grating-gated AlN/GaN HEMTs at mid-infrared frequencies.

The plasmon resonances of grating-gated AlN/GaN HEMTs can occur in wide frequency regions at mid-infrared frequencies. However, the lack of polarization properties research in grating-gated AlN/GaN HEMTs prevents the application potential. In order to solve the problem, the polarization properties in grating-gated AlN/GaN HEMTs at mid-infrared frequencies were studied in the paper. After using the optical transfer matrix method to calculate the dispersion curves in grating-gated AlN/GaN HEMTs, the plasmon polaritons in conductive channel and phonon polaritons in GaN layer occur under TM incident waves rather than TE incident waves. The phenomenon illustrates the potential of polarization-selectivity has existed in grating-gated AlN/GaN HEMTs. To study the polarization properties of grating-gated AlN/GaN HEMTs in detail, the electric field distribution and transmission properties of the structure were simulated in COMSOL. The results show the excellent polarization-selectivity at mid-infrared frequencies in grating-gated AlN/GaN HEMTs. The studies of these characteristics indicate the vast potential for using grating-gated AlN/GaN HEMTs to design mid-infrared polarizers, mid-infrared polarization state modulators and other devices in the future.

Strong Coupling of Carbon Quantum Dots in Liquid Crystals.

Carbon quantum dots (CDs) have recently received a tremendous amount of interest owing to their attractive optical properties. However, CDs have broad absorption and emission spectra limiting their application ranges. We herein, for the first time, show synthesis of water-soluble red emissive CDs with a very narrow line width (∼75 meV) spectral absorbance and hence demonstrate strong coupling of CDs and plasmon polaritons in liquid crystalline mesophases. The excited state dynamics of CDs has been studied by ultrafast transient absorption spectroscopy, and CDs display very stable and strong photoluminescence emission with a quantum yield of 35.4% and a lifetime of ∼2 ns. More importantly, we compare J-aggregate dyes with CDs in terms of their absorption line width, photostability, and ability to do strong coupling, and we conclude that highly fluorescent CDs have a bright future in the mixed light–matter states for emerging applications in future quantum technologies.

Real-space nanoimaging of THz polaritons in the topological insulator Bi2Se3

Plasmon polaritons in topological insulators attract attention from a fundamental perspective and for potential THz photonic applications. Although polaritons have been observed by THz far-field spectroscopy on topological insulator microstructures, real-space imaging of propagating THz polaritons has been elusive so far. Here, we show spectroscopic THz near-field images of thin Bi2Se3 layers (prototypical topological insulators) revealing polaritons with up to 12 times increased momenta as compared to photons of the same energy and decay times of about 0.48 ps, yet short propagation lengths. From the images we determine and analyze the polariton dispersion, showing that the polaritons can be explained by the coupling of THz radiation to various combinations of Dirac and massive carriers at the Bi2Se3 surfaces, massive bulk carriers and optical phonons. Our work provides critical insights into the nature of THz polaritons in topological insulators and establishes instrumentation and methodology for imaging of THz polaritons.

Tunable spin hall effect via hybrid polaritons around epsilon-near-zero on graphene-hBN heterostructures

We present a tunable spin Hall effect of light (SHEL) by introducing a monolayer of graphene on the hexagonal boron nitride (hBN). The interaction between the phonon polaritons in hBN and the plasmon polaritons in graphene can significantly enhance the SHEL around epsilon-near-zero (ENZ) near reststrahlen band-I (RB-I) in a very wide range of incident angles and compress it obviously in reststrahlen band-II (RB-II). The spin shifts can be obtained by adjusting the ratio of reflective coefficient and the phase difference for s- and p-waves which can be easily manipulated by the chemical potential. The effect of the tilted angle, thickness of hBN and incident angle on the SHEL is also discussed. These findings may lead to the potential applications for the nano-optical device based on the spin optics and the control of photons.

Middle- and far-infrared detector based on the plane collection of graphene strips

A concept of a middle- and far-infrared detector has been proposed. The detector is built as a planar collection of parallel graphene strips of different length and width. The feature of the detector scheme is the concurrent utilization of two different detection mechanisms: excitation in the given frequency range of low-frequency interband transitions inherent in armchair graphene strips and antenna resonances of strongly slowed-down surface waves (plasmon polaritons). It has been shown that matching these two resonances results in the essential detector signal amplification, thus providing an alternative way how to solve the problem of the low efficiency of resonant graphene antennas. An approach is proposed to analyze the design of such detectors, as well as to discuss the ways of tuning the both mechanisms.

THz pulse train generation through ultrafast development of surface plasmon-polariton modulation instability

Propagation of high-intensity electromagnetic waves in a waveguide structure could initiate nonlinear effects resulting in drastic changes of their spatial and temporal characteristics. We study the modulation instability effect induced by propagation of surface plasmon polaritons in a silver thin-film waveguide. The nonlinear Schrodinger equation for propagating surface plasmon wave is obtained. It is shown numerically that the modulation instability effect can give rise to ultrafast spatial redistribution and longitudinal localization of surface plasmon-polariton wave energy in subwavelength scale. The dependence of plasmon wave dispersion and nonlinear characteristics on metal film thickness is considered. We demonstrate that the use of films with the thickness varying along the waveguide length allows reduction of the generated pulse width and increase of frequency comb bandwidth. The proposed technique is promising for design of ultra-compact (tens of nm) optical generators delivering pulse trains with the repetition rate higher than 1 THz.