Searching for new plasmonic building blocks which offer tunability and design flexibility beyond noble metals is crucial for advancing the field of plasmonics. Herein, we report that solution-synthesized hexagonal Bi2Te3 nanoplates, in the absence of grating configurations, can exhibit multiple plasmon modes covering the entire visible range, as observed by transmission electron microscopy (TEM)-based electron energy-loss spectroscopy (EELS) and cathodoluminescence (CL) spectroscopy. Moreover, different plasmon modes are observed in the center and edge of the single Bi2Te3 nanoplate and a breathing mode is discovered for the first time in a non-noble metal. Theoretical calculations show that the plasmons observed in the visible range are mainly due to strong spin-orbit coupling induced metallic surface states of Bi2Te3. The versatility of shape- and size-engineered Bi2Te3 nanocrystals suggests exciting possibilities in plasmonics-enabled technology.

We used scattering-type scanning near-field optical microscopy (s-SNOM) to investigate the plasmonic properties of edges in well-defined graphene nanostructures, including sharp tapers, nanoribbons and nanogaps, which were all fabricated via the growth-etching chemical vapor deposition (GECVD) method. The obtained near-field images revealed the localized plasmon modes along the graphene nanoribbon; these modes strongly depended on the size of the graphene pattern, the angle of the tapered graphene and the infrared excitation wavelength. These interesting plasmon modes were verified by numerical simulations and explained by the reflection, and interference of electromagnetic waves at the graphene–SiO2 edge. The constructive interference at the graphene nanogap caused by charge accumulation was demonstrated for the first time. Using the infrared nanoimaging technique, greater plasmon broadening was observed in the zigzag edge than in the armchair edge. Our study suggests that graphene edges should be separated by an effective working distance to avoid the overlapping of localized plasmon modes, which is very important for the design of graphene-based plasmonic circuits and devices.

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The mechanical interaction between light and graded index media (both isotropic and anisotropic) is presented from the geometrical optics (GO) perspective. Utilizing Hamiltonian equations to determine ray trajectories combined with a description of the Lorentz force exerted on bound currents and charges, we provide a general method that we denote 'force tracing' for determining the direction and magnitude of the bulk and surface force density in arbitrarily anisotropic and inhomogeneous media. This technique provides the optical community with machinery which can give a good estimation of the force field distribution in different complex media, and with significantly faster computation speeds than full-wave methods allow. Comparison of force tracing against analytical solutions shows some unusual limitations of GO, which we also illustrate.Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. like behavior to some extent, while black-body radiation, the photoelectric effect and the Compton effect are related to the particle-like nature of photons. Distinguishing these two characteristics is crucial in gaining an intuitive understanding of the physics of light, but sometimes it can be baffling when these two views of the nature of light lead to contradictory conclusions in some circumstances. One such puzzling case is the long-lasting Abraham-Minkowski controversy, which is related to the momentum of photons in matter and the distribution of optical force (or stress) and torque within a medium.From the early days of electromagnetic wave theory, the pressure exerted by light on a body was of great interest. In 1891, Maxwell, using his celebrated equations, was able to calculate the momentum density of light in free space and predicted that '[concentrated] rays falling on a thin metallic disc, delicately suspended in a vacuum, might perhaps produce an observable mechanical effect' [1]. At the same time, using the second law of thermodynamics, Bartoli reached a similar conclusion [2]. Not long after that, the idea proposed by Maxwell and Bartoli was experimentally validated by Lebedev [3] and later confirmed by experiments carried out by Nichols and Hull [4,5]. In 1908 Minkowski derived the momentum density of light in dielectrics analytically, reaching the conclusion that a photon inside a medium of refractive index n carries a momentum equal to np, where p is the momentum of the photon in vacuum [6,7]. Conversely, Abraham formulated electromagnetic momentum conservation in a different way, which resulted in the conclusion of p n for the momentum of the photon within a medium [8,9]. This was the start of a controversy which lasted for a century; during this long period of time, there have been many efforts made by theoretical [10][11][12][13][14][15][16][17][18][19][20][21][22] and experimental [23][24][25] researchers to advocate either o...