Surface Phonon Polaritons Research Articles

Tailoring Surface Phonon Polariton on SiO2 by Ion-Beam Irradiation

Tailoring Surface Phonon Polariton on SiO₂ by Ion-Beam Irradiation

Giant Enhancement of Negative Friction by Resonant Coupling Between Localized Surface Phonon Polaritons and Graphene Plasmonics

Abstract Negative friction refers to a frictional force that acts in the same direction as the motion of an object, which has been predicted in terahertz (THz) gain systems [Phys. Rev. B 108 (4), 045406(2023)]. In this work, we investigate the enhancement of the negative friction experienced by nanospheres placed near a graphene substrate. We find that the magnitude of negative friction is related to the resonant coupling between the surface plasmon polaritons (SPPs) of the graphene and localized surface phonon-polaritons (LSPhP) of nanospheres. We exam nanospheres consisted of several different materials, including SiO2, SiC, ZnSe, NaCl, lnSb. Our results suggest that the LSPhP of NaCl nanospheres match effectively with the amplified SPPs of graphene sheets. The negative friction for NaCl nanospheres can be enhanced about one-to-two orders of magnitude compared to that of silica (SiO2) nanospheres. At the resonant peak of negative friction, the required quasi-Fermi energy of graphene is lower for NaCl nanospheres. Our finds hold great prospects for the mechanical manipulations of nanoscale particles.

Enhancing Near-Field Radiative Heat Transfer between Dissimilar Dielectric Media by Coupling Surface Phonon Polaritons to Graphene’s Plasmons

Enhancing Near-Field Radiative Heat Transfer between Dissimilar Dielectric Media by Coupling Surface Phonon Polaritons to Graphene’s Plasmons

Enhanced Cherenkov radiation in twisted hyperbolic Van der Waals crystals

AbstractCherenkov radiation in artificial structures experiencing strong radiation enhancements promises important applications in free‐electron quantum emitters, broadband light sources, miniaturized particle detectors, etc. However, the momentum matching condition between swift electrons and emitted photons generally restricts the radiation enhancement to a particular momentum. Efficient Cherenkov radiation over a wide range of momenta is highly demanded for many applications but still remains a challenging task. To this end, we explored the interaction between swift electrons and twisted hyperbolic Van der Waals crystals and observed enhanced Cherenkov radiation at the flatband resonance frequency. We show that, at the photonic magic angle of the twisted crystals, the electron momentum, once matching with that of the flatband photon, gives rise to a maximum energy loss (corresponding to the surface phonon generation), one‐order of magnitude higher than that in conventional hyperbolic materials. Such a significant enhancement is attributed to the excitation of flatband surface phonon polaritons over a broad momentum range. Our findings provide a feasible route for highly directional free‐electron radiation and radiation shaping.

Tunable thermal conductivity of surface phonon polaritons in SiC thin film

As an additional heat carrier besides phonons and electrons, the surface phonon polariton (SPhPs) possesses a large potential to increase the thermal conductivity. In this work, the influences of SPhP frequency, film thickness and film permittivity on the SPhP-contributed thermal conductivity of SiC thin films were probed. Results show that: there are two frequency zones which could lead to a much high thermal conductivity, i. e. the frequency which approaching zero and the frequency in singularity zone. The thermal conductivity decreases with the increase of the film thickness, following a power-function relationship, and a thin film with a thickness of 10-nm could have a thermal conductivity higher than 1×104 W·m−1·K−1. However, the experimental observation of this high thermal conductivity is still difficult because of the size effect of the film length. The thermal conductivity will increase with the decrease of the imaginary part of the film permittivity and/or increase of the real part of the film permittivity, and there is approximately a reciprocal dependence of thermal conductivity on the imaginary part of the film permittivity. The thermal conductivity could be tuned by several times with tailoring its permittivity through adding fillers in it or adding dopant in it. This work provides some potential methods to tune the SPhP thermal conductivity in SiC thin film, which could help its application in microscale heat dissipation.

Advancing high thermal conductivity: novel theories, innovative materials, and applications in thermal management technologies.

Effective thermal management is crucial for the performance and stability of modern electronics, emphasizing the demand for high thermal conductivity (κ). This review summarizes the latest development in highκ, discussing the emerging theories, innovative materials and practical applications for interfacial heat dissipation. Unique phononic thermal transport behaviors are discussed, including four phonon-phonon scattering, hydrodynamic phonons, surface phonon-polaritons, and more. The review also highlights innovative materials with highκ, such as two-dimensional pentagonal structures, boron carbon nitrogen structures, hexagonal boron arsenide andθ-phase tantalum nitride. In addition, the potential of polymer composites reinforced with highκfillers and surface engineering for advanced electronic applications are also discussed. By integrating these theoretical approaches and material innovations, this review offers comprehensive strategies for enhancing thermal management in modern electronic devices.

Resonant Raman Scattering of Surface Phonon Polaritons Mediated by Excitons in WSe2 Films

Resonant Raman Scattering of Surface Phonon Polaritons Mediated by Excitons in WSe₂ Films

Surface phonon activation for broadband high emissivity via textured structure on TiO2 coating

In the pursuit of developing broadband high emissivity coatings for metallic radiation thermal protection, conventional approaches often involve complex photonic structures or the incorporation of transition metals and rare earth additives, which pose significant technological challenges and environmental concerns. Here, we present a straightforward and eco-friendly surface structuring strategy for creating a high emissivity TiO2 coating on titanium, eliminating the need for environmentally hazardous additives. By controlling surface micropore diameter to ∼6 um through soft-sparking discharge, we successfully engineered a textured surface that effectively mitigates the intrinsic emissivity dip of planar TiO2 at wavelengths with weak polarization extinction (3–8 µm) and strong polarization resonance (>12 µm). Finite-difference time-domain (FDTD) simulations highlighted the crucial role of micropores in confining the incident electric field, maximizing the absorption potential of surface phonon polaritons. This improvement yields an impressive emissivity of 0.83 across the thermal infrared spectrum. The coating also demonstrated robust resistance to oxidation and retained its high emissivity at elevated temperatures, presenting a promising solution for sustainability in spacecraft and electronic applications.

Temperature-dependent optical constants of vanadium dioxide thin films deposited on polar dielectrics

Coating polar dielectrics with thin film vanadium dioxide (VO2) enables one to exploit the temperature-dependent phase transition within VO2 to actively tune and modulate surface phonon polaritons at mid-infrared. However, controlling the behavior of such systems requires intimate knowledge of the temperature-dependent optical constants of VO2, which depend greatly on the growth conditions and substrate material. Here, we accurately determine the complex optical constants of VO2 on polar dielectrics across the insulator-to-metal phase transition (IMT) using only normal incident reflectance spectra by analyzing the reflectance with Kramers–Kronig relations and thin film Fresnel equations. This non-ellipsometry technique offers an advantage in determining the refractive index using a standard infrared spectrometer.

Spectroscopic and Interferometric Sum-Frequency Imaging of Strongly Coupled Phonon Polaritons in SiC Metasurfaces.

Phonon polaritons enable waveguiding and localization of infrared light with extreme confinement and low losses. The spatial propagation and spectral resonances of such polaritons are usually probed with complementary techniques such as near-field optical microscopy and far-field reflection spectroscopy. Here, infrared-visible sum-frequency spectro-microscopy is introduced as a tool for spectroscopic imaging of phonon polaritons. The technique simultaneously provides sub-wavelength spatial resolution and highly-resolved spectral resonance information. This is implemented by resonantly exciting polaritons using a tunable infrared laser and wide-field microscopic detection of the upconverted light. The technique is employed to image hybridization and strong coupling of localized and propagating surface phonon polaritons in a metasurface of SiC micropillars. Spectro-microscopy allows to measure the polariton dispersion simultaneously in momentum space by angle-dependent resonance imaging, and in real space by polariton interferometry. Notably, it is possible to directly image how strong coupling affects the spatial localization of polaritons, inaccessible with conventional spectroscopic techniques. The formation of edge states is observed at excitation frequencies where strong coupling prevents polariton propagation into the metasurface. The technique is applicable to the wide range of polaritonic materials with broken inversion symmetry and can be used as a fast and non-perturbative tool to image polariton hybridization andpropagation.

Spatially Resolved Near Field Spectroscopy of Vibrational Polaritons at the Small N Limit.

Vibrational polaritons, which have been primarily studied in Fabry-Pérot cavities with a large number of molecules (N ∼ 106-1010) coupled to the resonator mode, exhibit various experimentally observed effects on chemical reactions. However, the exact mechanism is elusively understood from the theoretical side, as the large number of molecules involved in an experimental strong coupling condition cannot be represented completely in simulations. This discrepancy between theory and experiment arises from computational descriptions of polariton systems typically being limited to only a few molecules, thus failing to represent the experimental conditions adequately. To address this mismatch, we used surface phonon polariton (SPhP) resonators as an alternative platform for vibrational strong coupling. SPhPs exhibit strong electromagnetic confinement on the surface and thus allow for coupling to a small number of molecules. As a result, this platform can enhance nonlinearity and slow down relaxation to the dark modes. In this study, we fabricated a pillar-shaped quartz resonator and then coated it with a thin layer of cobalt phthalocyanine (CoPc). By employing scattering-type scanning near-field optical microscopy (s-SNOM), we spatially investigated the dependency of vibrational strong coupling on the spatially varying electromagnetic field strength and demonstrated strong coupling with 38,000 molecules only-reaching to the small N limit. Through s-SNOM analysis, we found that strong coupling was observed primarily on the edge of the quartz pillar and the apex of the s-SNOM tip, where the maximum field enhancement occurs. In contrast, a weak resonance signal and lack of coupling were observed closer to the center of the pillar. This work demonstrates the importance of spatially resolved polariton systems in nanophotonic platforms and lays a foundation to explore polariton chemistry and chemical dynamics at the small N limit-one step closer to reconcile with high-level quantum calculations.

Highly confined epsilon-near-zero and surface phonon polaritons in SrTiO3 membranes

Recent theoretical studies have suggested that transition metal perovskite oxide membranes can enable surface phonon polaritons in the infrared range with low loss and much stronger subwavelength confinement than bulk crystals. Such modes, however, have not been experimentally observed so far. Here, using a combination of far-field Fourier-transform infrared (FTIR) spectroscopy and near-field synchrotron infrared nanospectroscopy (SINS) imaging, we study the phonon polaritons in a 100 nm thick freestanding crystalline membrane of SrTiO3 transferred on metallic and dielectric substrates. We observe a symmetric-antisymmetric mode splitting giving rise to epsilon-near-zero and Berreman modes as well as highly confined (by a factor of 10) propagating phonon polaritons, both of which result from the deep-subwavelength thickness of the membranes. Theoretical modeling based on the analytical finite-dipole model and numerical finite-difference methods fully corroborate the experimental results. Our work reveals the potential of oxide membranes as a promising platform for infrared photonics and polaritonics.

Long Propagating Polaritonic Heat Transfer: Shaping Radiation to Conduction.

Surface phonon polaritons (SPhPs) originate from the coupling of mid-IR photons and optical phonons, generating evanescent waves along the polar dielectric surface. The emergence of SPhPs gives rise to a phase of quantum matter that facilitates long-range energy transfer (100s μm-scale). Albeit of the recent experimental progress to observe the enhanced thermal conductivity of polar dielectric nanostructures mediated by SPhPs, the potential mechanism to present the high thermal conductivity beyond the Landauer limit has not been addressed. Here, we revisit the comprehensive theoretical framework to unify the distinct pictures of two heat transfer mechanisms by conduction and radiation. We first designed our experimental platform to distinguish contributions of two distinct fundamental modes of SPhPs, resulting in far-field radiation and long propagating conduction, respectively, by tuning the configuration of a nanostructured heat channel integrated into the thermometer. We could effectively control the transmission of long-propagating SPhPs to influence the apparent thermal conductivity of the nanostructure. This study reveals the high thermal conductance of 1.63 nW/K by a fast SPhP mode comparable to that by classical phonons, with measurements showing apparent conductivity values of up to 2 W/m·K at 515 K. The origin of the enhanced thermal conductivity was exploited by observing the interference of dispersive evanescent waves by double heat channels. Furthermore, our experimental observations of length-dependent thermal conductance by SPhPs are in good agreement with the revisited Landauer formula to illustrate a polaritonic mode of heat conduction, considering the dispersive nature of radiation not limited to the physical boundaries of a solid object yet directionally guided along the surface.

Enhancing mid-infrared surface phonon polariton modes: optimization of structural parameters in Nb-doped SrTiO3 with hole array structures for advanced infrared sensors

This study utilized the finite difference time domain method to investigate the mid infrared surface phonon polaritons and localized surface phonon resonances in undoped and niobium (Nb)-doped SrTiO3 (STO) with planar and holes array structures. Research has shown that Nb-doped STO operates in the Reststrahlen band of 8.06–18.48 µm, providing a wider spectral response than undoped STO (12.58–18.26 µm) and effectively covering the atmospheric window of long wave infrared. This indicates that the increase in virtual permittivity has the least impact on spectral broadening, indicating that the new infrared sensor technology has broad prospects. The optimization of structural parameters, including the period, filling factor, and depth of STO holes array, as well as the response to changes in incident light angle, is crucial for guiding the design of high-performance optoelectronic devices. In addition, this study explored the excitation of four resonant modes within a holes array and analyzed their relationship with array parameters to enhance the design of optoelectronic applications.

Enhanced Far-Field Thermal Radiation through a Polaritonic Waveguide.

We experimentally demonstrate the enhancement of the far-field thermal radiation between two nonabsorbent Si microplates coated with energy-absorbent silicon dioxide (SiO_{2}) nanolayers supporting the propagation of surface phonon polaritons. By measuring the radiative thermal conductance between two coated Si plates, we find that its values are twice those obtained without the SiO_{2} coating. This twofold increase results from the hybridization of polaritons with guided modes inside Si and is well predicted by fluctuational electrodynamics and an analytical model based on a two-dimensional density of polariton states. These findings could be applied to thermal management in microelectronics, silicon photonics, energy conversion, atmospheric sciences, and astrophysics.

Lifetime and Molecular Coupling in Surface Phonon Polariton Resonators.

Surface phonon polariton (SPhP) modes in polar semiconductors offer a low-loss platform for infrared nanophotonics and sensing. However, the efficient design of polariton-enhanced sensors requires a quantitative understanding of how to engineer the frequency and lifetime of SPhPs in nanophotonic structures. Here, we study organ-pipe resonances in 4H-SiC trenches as a prototype system for infrared sensing. We use a transmission line framework that accounts for the field distribution within the trench, accurately predicting mode frequency and lifetime when compared against finite element method (FEM) electromagnetic calculations. Accounting for the electric field profile across the gap is critical in our model to accurately predict mode frequencies, quality factor (Q factor), and reflectance, outperforming previous circuit models developed in the literature. Beyond structural simulation, our model can provide insights into the frequency ranges in the Reststrahlen band where enhanced sensor activity should be present. The radiative lifetime is significantly enlarged close to the longitudinal optic phonon, restricting sensor efficiency at this wavelength range. This pushes the optimal frequency for sensing closer to the center of the Reststrahlen band than might be naively expected. This model ultimately demonstrates the primary challenge of designing SPhP-based sensors: only a relatively narrow region of the Reststrahlen band offers efficient sensing, guiding future designs for infrared spectroscopy.

Direct programming of confined surface phonon polariton resonators with the plasmonic phase-change material In3SbTe2

Tailoring light-matter interaction is essential to realize nanophotonic components. It can be achieved with surface phonon polaritons (SPhPs), an excitation of photons coupled with phonons of polar crystals, which also occur in 2d materials such as hexagonal boron nitride or anisotropic crystals. Ultra-confined resonances are observed by restricting the SPhPs to cavities. Phase-change materials (PCMs) enable non-volatile programming of these cavities based on a change in the refractive index. Recently, the plasmonic PCM In3SbTe2 (IST) was introduced which can be reversibly switched from an amorphous dielectric state to a crystalline metallic one in the entire infrared to realize numerous nanoantenna geometries. However, reconfiguring SPhP resonators to modify the confined polaritons modes remains elusive. Here, we demonstrate direct programming of confined SPhP resonators by phase-switching IST on top of a polar silicon carbide crystal and investigate the strongly confined resonance modes with scanning near-field optical microscopy. Reconfiguring the size of the resonators themselves result in enhanced mode confinements up to a value of λ/35.\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{{{{\\boldsymbol{\\lambda }}}}}}{{{{{\\boldsymbol{/}}}}}}{{{{{\\boldsymbol{35}}}}}}{{{{{\\boldsymbol{.}}}}}}$$\\end{document} Finally, unconventional cavity shapes with complex field patterns are explored as well. This study is a first step towards rapid prototyping of reconfigurable SPhP resonators that can be easily transferred to hyperbolic and anisotropic 2d materials.

Fano resonance and enhanced sensing in the excitation of the surface phonon polariton

The surface phonon polariton is a collective oscillation mode of phonons and incident electromagnetic waves in polar dielectric materials. Compared with the surface plasmon polariton, it has low loss and can be applied to the mid-infrared band. A surface phonon resonance sensor based on waveguide-coupling is proposed. The sensor structure is a typical Kretschmann configuration consisting of a germanium (Ge) prism, a silicon carbide (SiC) layer, an indium selenide (In2Se3) film, a titanium dioxide (TiO2) film, and the surrounding dielectric. The reflectivity possesses significant asymmetric Fano resonance dips. In sensing applications, the waveguide-coupling structure yields a sensitivity by intensity of 11278RIU−1 and a figure of merit of 10344RIU−1. Our investigation provides an alternative method for refractive index sensing, thus opening up opportunities for the design of various phonon devices based on Fano resonance.

Temporal dynamics of surface phonon polaritons in polar dielectric nanoparticles with nonlocality

Surface phonon polaritons (SPhPs) supported by polar dielectrics have been a promising platform for nanophotonics in mid-infrared spectral range. In this work, the temporal dynamic behavior of polar dielectric nanoparticles without (or with) spatial dispersion/nonlocality driven by the ultrashort Gaussian pulses is carried out. We demonstrate that three possible scenarios for the temporal evolutions of the dipole moment including ultrafast oscillations with the decay, exponential decay, and keeping a Gaussian shape exist, when the pulse duration of the incident field is much shorter than, similar to, and much longer than the localized SPhP lifetime. Once the nonlocal effect is considered, the oscillation period becomes large slightly, and the exponential decay turns fast. Furthermore, nonlocality-induced novel temporal behavior is found such as the decay with long-period oscillations when the center frequency of the incident pulse lies at the frequency of adjacent longitudinal resonant modes. The positive and negative time-shifts of the dielectric response reveal that the excitation of the dipole moment will be delayed or advanced. These temporal evolutions can pave the way towards potential applications in the modulation of ultrafast signals for the mid-infrared optoelectronic nanodevices.

Multiplication of the orbital angular momentum of phonon polaritons via sublinear dispersion

Optical vortices (OVs) promise to greatly enhance optical information capacity via orbital angular momentum multiplexing. The need for the on-chip integration of orbital angular momentum technologies has prompted research into subwavelength-confined polaritonic OVs. However, the topological order imprinted by the structure used for transduction from free-space beams to surface polaritons is inherently fixed after fabrication. Here we overcome this limitation via dispersion-driven topological charge multiplication. We switch the OV topological charge within a small frequency range (~3%) by leveraging the strong sublinear dispersion of low-loss surface phonon polaritons on silicon carbide membranes. Applying the Huygens principle, we quantitatively evaluate the topological order of experimental OVs detected by near-field imaging. We further explore the deuterogenic effect, which predicts the coexistence of multiple topological charges in higher-order polaritonic OVs. Our work demonstrates a viable method to manipulate the topological charge of polaritonic OVs, paving the way for the exploration of novel orbital-angular-momentum-enabled light–matter interactions at mid-infrared frequencies.