Explore the vast range of titles available.

Plasmonic nanostructures can concentrate light and enhance light-matter interactions in the subwavelength domain, which is useful for photodetection, light emission, optical biosensing, and spectroscopy. However, conventional plasmonic devices and systems are typically optimized for the operation in a single wavelength band and thus are not suitable for multiband nanophotonics applications that either prefer nanoplasmonic enhancement of multiphoton processes in a quantum system at multiple resonant wavelengths or require wavelength-multiplexed operations at nanoscale. To overcome the limitations of “single-resonant plasmonics,” we need to develop the strategies to achieve “multiresonant plasmonics” for nanoplasmonic enhancement of light-matter interactions at the same locations in multiple wavelength bands. In this review, we summarize the recent advances in the study of the multiresonant plasmonic systems with spatial mode overlap. In particular, we explain and emphasize the method of “plasmonic mode hybridization” as a general strategy to design and build multiresonant plasmonic systems with spatial mode overlap. By closely assembling multiple plasmonic building blocks into a composite plasmonic system, multiple nonorthogonal elementary plasmonic modes with spectral and spatial mode overlap can strongly couple with each other to form multiple spatially overlapping new hybridized modes at different resonant energies. Multiresonant plasmonic systems can be generally categorized into three types according to the localization characteristics of elementary modes before mode hybridization, and can be based on the optical coupling between: (1) two or more localized modes, (2) localized and delocalized modes, and (3) two or more delocalized modes. Finally, this review provides a discussion about how multiresonant plasmonics with spatial mode overlap can play a unique and significant role in some current and potential applications, such as (1) multiphoton nonlinear optical and upconversion luminescence nanodevices by enabling a simultaneous enhancement of optical excitation and radiation processes at multiple different wavelengths and (2) multiband multimodal optical nanodevices by achieving wavelength multiplexed optical multimodalities at a nanoscale footprint.

The properties of propagating surface plasmon polaritons (SPPs) along one-dimensional metal structures have been investigated for more than 10 years and are now well understood. Because of the high confinement of electromagnetic energy, propagating SPPs have been considered to represent one of the best potential ways to construct next-generation circuits that use light to overcome the speed limit of electronics. Many basic plasmonic components have already been developed. In this review, researches on plasmonic waveguides are reviewed from the perspective of plasmonic circuits. Several circuit components are constructed to demonstrate the basic function of an optical digital circuit. In the end of this review, a prototype for an SPP-based nanochip is proposed, and the problems associated with building such plasmonic circuits are discussed. A plasmonic chip that can be practically applied is expected to become available in the near future. Plasmonics: nanophotonic circuitry The prospects for creating sophisticated nanophotonic circuits by harnessing the opportunities provided by plasmonics are exciting. Yurui Fang and Mengtao Sun from the Beijing National Laboratory for Condensed Matter Physics review recent progress in the development of various components and devices for generating, manipulating and detecting surface plasmon polaritons — tightly confined waves that can be excited by light at the interface between a metal and a dielectric. Their small size offers opportunities for constructing photonic devices that are smaller than the wavelength of light, a major barrier to the miniaturization of optical integrated circuits. Fang and Sun describe how nanoscale waveguides, multiplexers, lasers, high-speed modulators, logic gates and detectors for surface plasmon polaritons are all coming to fruition. They also consider the future prospects of this technology.

Ferroelectricity, a spontaneous and reversible electric polarization, is found in certain classes of van der Waals (vdW) materials. The discovery of ferroelectricity in twisted vdW layers provides new opportunities to engineer spatially dependent electric and optical properties associated with the configuration of moiré superlattice domains and the network of domain walls. Here, we employ near-field infrared nano-imaging and nano-photocurrent measurements to study ferroelectricity in minimally twisted WSe 2 . The ferroelectric domains are visualized through the imaging of the plasmonic response in a graphene monolayer adjacent to the moiré WSe 2 bilayers. Specifically, we find that the ferroelectric polarization in moiré domains is imprinted on the plasmonic response of the graphene. Complementary nano-photocurrent measurements demonstrate that the optoelectronic properties of graphene are also modulated by the proximal ferroelectric domains. Our approach represents an alternative strategy for studying moiré ferroelectricity at native length scales and opens promising prospects for (opto)electronic devices. Recent experiments have shown the formation of ferroelectric domains in twisted van der Waals bilayers. Here, the authors report near-field infrared nano-imaging and nano-photocurrent measurements to investigate ferroelectricity in minimally twisted WSe 2 by visualizing the plasmonic and photo-thermoelectric response of an adjacent graphene monolayer.

Surface plasmonic sensors have been widely used in biology, chemistry, and environment monitoring. These sensors exhibit extraordinary sensitivity based on surface plasmon resonance (SPR) or localized surface plasmon resonance (LSPR) effects, and they have found commercial applications. In this review, we present recent progress in the field of surface plasmonic sensors, mainly in the configurations of planar metastructures and optical-fiber waveguides. In the metastructure platform, the optical sensors based on LSPR, hyperbolic dispersion, Fano resonance, and two-dimensional (2D) materials integration are introduced. The optical-fiber sensors integrated with LSPR/SPR structures and 2D materials are summarized. We also introduce the recent advances in quantum plasmonic sensing beyond the classical shot noise limit. The challenges and opportunities in this field are discussed.

A compact microwave bandpass filter with fishbone-shaped and hourglass-shaped groove structures based on substrate integrated plasmonic waveguide (SIPW) and spoof surface plasmon polariton (SSPP) is proposed and investigated. The dispersion and transmission characteristics of the proposed unit-cell structures of SSPP and SIPW were analyzed numerically, respectively. Numerical results indicate that the high and low cut-off frequencies of the bandpass filter can be independently adjusted by changing geometric parameters of unit-cell structures of SSPP and SIPW, respectively. The proposed microwave bandpass filter has a smaller electrical size because of its better electromagnetic (EM) field constraints than the traditional SIW ones with combed groove lines SSPPs. To verify the design method and concept, a microwave bandpass filter with fishbone-shaped and hourglass-shaped groove structures has been designed, fabricated, and measured. The results demonstrate that the proposed passband is in the range of 7.3–10.1 GHz, the return loss is higher than 10 dB and the insertion loss is less than 2 dB. The microwave bandpass filter is very compact in size, only about 0.99 λ 0  × 0.35 λ 0 , where λ 0 is the wavelength at the center frequency.

Temporal and spectral control of hot electron decay can be achieved using specific plasmonic nanostructures. The interaction of light and matter in metallic nanosystems is mediated by the collective oscillation of surface electrons, called plasmons 1 . After excitation, plasmons are absorbed by the metal electrons through inter- and intraband transitions, creating a highly non-thermal distribution of electrons 2 , 3 , 4 . The electron population then decays through electron–electron interactions, creating a hot electron distribution within a few hundred femtoseconds, followed by a further relaxation via electron–phonon scattering on the timescale of a few picoseconds 5 , 6 , 7 , 8 . In the spectral domain, hot plasmonic electrons induce changes to the plasmonic resonance of the nanostructure by modifying the dielectric constant of the metal 5 , 9 . Here, we report on the observation of anomalously strong changes to the ultrafast temporal and spectral responses of these excited hot plasmonic electrons in hybrid metal/oxide nanostructures as a result of varying the geometry and composition of the nanostructure and the excitation wavelength. In particular, we show a large ultrafast, pulsewidth-limited contribution to the excited electron decay signal in hybrid nanostructures containing hot spots. The intensity of this contribution correlates with the efficiency of the generation of highly excited surface electrons. Using theoretical models, we attribute this effect to the generation of hot plasmonic electrons from hot spots. We then develop general principles to enhance the generation of energetic electrons through specifically designed plasmonic nanostructures that could be used in applications where hot electron generation is beneficial, such as in solar photocatalysis, photodetectors and nonlinear devices 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 .

For almost two decades, researchers have observed the preservation of the quantum statistical properties of bosons in a large variety of plasmonic systems. In addition, the possibility of preserving nonclassical correlations in light-matter interactions mediated by scattering among photons and plasmons stimulated the idea of the conservation of quantum statistics in plasmonic systems. It has also been assumed that similar dynamics underlie the conservation of the quantum fluctuations that define the nature of light sources. So far, plasmonic experiments have been performed in nanoscale systems in which complex multiparticle interactions are restrained. Here, we demonstrate that the quantum statistics of multiparticle systems are not always preserved in plasmonic platforms and report the observation of their modification. Moreover, we show that optical near fields provide additional scattering paths that can induce complex multiparticle interactions. Remarkably, the resulting multiparticle dynamics can, in turn, lead to the modification of the excitation mode of plasmonic systems. These observations are validated through the quantum theory of optical coherence for single- and multi-mode plasmonic systems. Our findings unveil the possibility of using multiparticle scattering to perform exquisite control of quantum plasmonic systems. So far, experimental results have favoured the often unstated assumption that quantum statistical properties of multiparticle systems are preserved in plasmonic platforms. Here, the authors show how multiparticle interference in photon-plasmon scattering can modify the excitation mode of plasmonic systems.

The authors report the observation of plasmons that exhibit quantized velocities in carbon nanotubes. Surface plasmons 1 , collective oscillations of conduction electrons, hold great promise for the nanoscale integration of photonics and electronics 1 , 2 , 3 , 4 . However, nanophotonic circuits based on plasmons have been significantly hampered by the difficulty in achieving broadband plasmonic waveguides that simultaneously exhibit strong spatial confinement, a high quality factor and low dispersion. Quantum plasmons, where the quantum mechanical effects of electrons play a dominant role, such as plasmons in very small metal nanoparticles 5 , 6 and plasmons affected by tunnelling effects 7 , can lead to novel plasmonic phenomena in nanostructures. Here, we show that a Luttinger liquid 8 , 9 of one-dimensional Dirac electrons in carbon nanotubes 10 , 11 , 12 , 13 exhibits quantum plasmons that behave qualitatively differently from classical plasmon excitations. The Luttinger-liquid plasmons propagate at ‘quantized’ velocities that are independent of carrier concentration or excitation wavelength, and simultaneously exhibit extraordinary spatial confinement and high quality factor. Such Luttinger-liquid plasmons could enable novel low-loss plasmonic circuits for the subwavelength manipulation of light.

Structural coloring is production of color by surfaces that have microstructure fine enough to interfere with visible light; this phenomenon provides a novel paradigm for color printing. Plasmonic color is an emergent property of the interaction between light and metallic surfaces. This phenomenon can surpass the diffraction limit and achieve near unlimited lifetime. We categorize plasmonic color filters according to their designs (hole, rod, metal–insulator–metal, grating), and also describe structures supported by Mie resonance. We discuss the principles, and the merits and demerits of each color filter. We also discuss a new concept of color filters with tunability and reconfigurability, which enable printing of structural color to yield dynamic coloring at will. Approaches for dynamic coloring are classified as liquid crystal, chemical transition and mechanical deformation. At the end of review, we highlight a scale-up of fabrication methods, including nanoimprinting, self-assembly and laser-induced process that may enable real-world application of structural coloring.