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Plasmons in doped graphene exhibit relatively large confinement and long lifetime compared to noble-metal plasmons. Here, we study the propagation properties of plasmons guided along individual and interacting graphene nanoribbons. Besides their tunability via electrostatic gating, an additional handle to control these excitations is provided by the dielectric environment and the relative arrangement of the interacting waveguides. Plasmon interaction

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Recently, we witnessed a tremendous effort to conquer the realm of acoustics as a possible playground to test with sound waves topologically protected wave propagation. Acoustics differ substantially from photonic and electronic systems since longitudinal sound waves lack intrinsic spin polarization and breaking the time-reversal symmetry requires additional complexities that both are essential in mimicking the quantum effects leading to topologically robust sound propagation. In this article, we review the latest efforts to explore with sound waves topological states of quantum matter in two-and three-dimensional systems where we discuss how spin and valley degrees of freedom appear as highly novel ingredients to tailor the flow of sound in the form of one-way edge modes and defect-immune protected acoustic waves. Both from a theoretical stand point and based on contemporary experimental verifications, we summarize the latest advancements of the flourishing research frontier on topological sound. arXiv:1807.09544v1 [cond-mat.mes-hall] 25 Jul 2018Recently, another discrete degree of freedom, namely the valley, has also been proposed to realize a topological state, known as the valley Hall effect (VHE), which is related to valleytronics 9,10 . Valley refers to the two energy extrema of the band structure in momentum space, at which the Berry curvature exhibits opposite signs and therefore its integral over the full Brillouin zone is zero, while the integral within each valley is non-zero. As a result, the system shows a valley-selective topologically non-trivial property (Fig. 1(d)). It is

A complete landscape is presented of the acoustic transmission properties of subwavelength apertures (slits and holes). First, we study the emergence of Fabry-Perot resonances in single apertures. When these apertures are placed in a periodic fashion, a new type of transmission resonance appears in the spectrum. We demonstrate that this resonance stems from the excitation of an acoustic guided wave that runs along the plate, which hybridizes strongly with the Fabry-Perot resonances associated with waveguide modes in single apertures. A detailed discussion of the similarities and differences with the electromagnetic case is also given.

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We study a class of acoustic metamaterials formed by layers of perforated plates and producing negative refraction and backward propagation of sound. A slab of such material is shown to act as a perfect acoustic lens, yielding images with subwavelength resolution over large distances. Our study constitutes a nontrivial extension of similar concepts from optics to acoustics, capable of sustaining negative refraction over extended angular ranges, with potential application to enhanced imaging for medical and detection purposes, acoustofluidics, and sonochemistry. DOI: 10.1103/PhysRevLett.108.124301 PACS numbers: 43.35.+d, 42.79.Dj, 81.05.Xj Optical negative refraction is a counterintuitive phenomenon that consists in bending light the wrong way at the interface between suitably engineered materials. Homogeneous substances with refraction indices of opposite signs provide an ideal combination on which this effect can take place. Over four decades ago, Veselago [1] realized that a material with simultaneous negative magnetic permeability and electric permittivity must have negative index and, therefore, can produce negative refraction. Subsequently, Pendry [2] showed that a slab of such material can amplify evanescent fields, from which a perfect lens can be constructed, capable of yielding images with deep subwavelength resolution. These concepts have been realized in artificial metamaterials, textured on a small scale compared to the wavelength and displaying homogeneous resonant electric and magnetic response [3,4].Inspired by these exotic optical phenomena, the quest for acoustic superlensing and negative refraction started with the prediction of negative index of refraction in materials exhibiting negative effective mass density and negative bulk modulus at the operating frequency [5]. In this context, several acoustic metamaterial designs have been proposed containing resonators in the form of coated metallic spheres [6], lumped elements [7], or perforations [8]. However, isotropic acoustic negative-index materials have not been experimentally realized to date, despite a long tradition of sound control using resonant linear devices [9,10], including applications to diffraction-limited imaging [11]. An alternative approach to acoustic negative refraction and lensing is suggested by electromagnetic metamaterials relying on anisotropy [12].In this Letter, we show that a holey anisotropic metamaterial can exert subwavelength control over sound waves beyond what is achieved with naturally occurring materials. We predict that, for appropriate choices of geometrical parameters, these metamaterials support negative refraction, backward-wave propagation along a direction opposite with respect to the acoustic energy flow, and subwavelength imaging with both the source and the image situated many wavelengths away from the material. Acoustic subwavelength control can be advantageous for (bio)medical ultrasonography and diagnostic imaging [13], acoustofluidic steering of microparticles and microorganisms [14], and sono...