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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