We point out that plasmons in doped graphene simultaneously enable low-losses and significant wave localization for frequencies below that of the optical phonon branch ω Oph ≈ 0.2 eV. Large plasmon losses occur in the interband regime (via excitation of electron-hole pairs), which can be pushed towards higher frequencies for higher doping values. For sufficiently large dopings, there is a bandwidth of frequencies from ω Oph up to the interband threshold, where a plasmon decay channel via emission of an optical phonon together with an electron-hole pair is nonegligible. The calculation of losses is performed within the framework of a random-phase approximation and number conserving relaxation-time approximation. The measured DC relaxation-time serves as an input parameter characterizing collisions with impurities, whereas the contribution from optical phonons is estimated from the influence of the electron-phonon coupling on the optical conductivity. Optical properties of plasmons in graphene are in many relevant aspects similar to optical properties of surface plasmons propagating on dielectric-metal interface, which have been drawing a lot of interest lately because of their importance for nanophotonics. Therefore, the fact that plasmons in graphene could have low losses for certain frequencies makes them potentially interesting for nanophotonic applications.

We show that a Hamiltonian with Weyl points can be realized for ultracold atoms using laser-assisted tunneling in three-dimensional optical lattices. Weyl points are synthetic magnetic monopoles that exhibit a robust, three-dimensional linear dispersion, identical to the energy-momentum relation for relativistic Weyl fermions, which are not yet discovered in particle physics. Weyl semimetals are a promising new avenue in condensed matter physics due to their unusual properties such as the topologically protected "Fermi arc" surface states. However, experiments on Weyl points are highly elusive. We show that this elusive goal is well within experimental reach with an extension of techniques recently used in ultracold gases. DOI: 10.1103/PhysRevLett.114.225301 PACS numbers: 67.85.-d, 03.65.Vf, 03.75.Lm In relativistic quantum field theory there are three types of fermions: Dirac, Majorana, and Weyl fermions [1]. The latter two have never been observed. It was conjectured that neutrinos could be Weyl fermions before the discovery of neutrino oscillations ruled out such a possibility. Nowadays, there is a great excitement on Weyl semimetals: gapless topological states of matter with bulk low-energy electrons behaving as Weyl fermions, and intriguing "Fermi arc" topological surface states [2][3][4]. Besides the fundamental importance of Weyl fermions and related phenomena such as the Adler-Bell-Jackiw chiral anomaly, the topological surface states of Weyl semimetals also hold great potential for applications [3]. These systems followed the development of topological insulators [5,6], emphasizing the role of band topology in describing exotic phases of matter. However, experiments on Weyl fermions are highly elusive.Recent experiments on synthetic magnetic fields in ultracold atomic gases [7][8][9][10][11][12][13][14][15][16][17], alongside advances in photonics [18][19][20][21][22][23][24], have propelled these systems as promising platforms for investigating topological effects and novel states of matter (see for reviews). However, Weyl points have been scarcely addressed in these fields [24,[30][31][32][33]. In photonics, a double gyroid photonic crystal with broken time reversal and/or parity symmetry was predicted to have Weyl points [24]. Theoretical lattice models possessing Weyl points [30,32,33], and Weyl spin-orbit coupling [31], were studied in the context of ultracold atomic gases. Because of the elusive nature of Weyl fermions, a viable and possibly simple scheme for their experimental realization in ultracold atomic gases would be of great importance, exploiting advantages of atomic systems to contribute to Weyl physics research across disciplines.Here, we propose the realization of the Weyl Hamiltonian for ultracold atoms in a straightforward modification of the experimental system that was recently employed to obtain the Harper Hamiltonian [12]. As an example of phenomena inherent to Weyl points, but most suitable for observing in ultracold systems, we discuss the unique spherical-shell expansion ...

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It is shown that thermally excited plasmon-polariton modes can strongly mediate, enhance and \emph{tune} the near-field radiation transfer between two closely separated graphene sheets. The dependence of near-field heat exchange on doping and electron relaxation time is analyzed in the near infra-red within the framework of fluctuational electrodynamics. The dominant contribution to heat transfer can be controlled to arise from either interband or intraband processes. We predict maximum transfer at low doping and for plasmons in two graphene sheets in resonance, with orders-of-magnitude enhancement (e.g. $10^2$ to $10^3$ for separations between $0.1\mu m$ to $10nm$) over the Stefan-Boltzmann law, known as the far field limit. Strong, tunable, near-field transfer offers the promise of an externally controllable thermal switch as well as a novel hybrid graphene-graphene thermoelectric/thermophotovoltaic energy conversion platform.Comment: 4 pages, 3 figure

The recent proposal of optical induction for producing nonlinear photonic lattices has revolutionized the study of nonlinear waves in waveguide arrays. In particular, it enabled the first observation of (2+1) dimensional lattice solitons, which were the first 2D solitons observed in any nonlinear periodic system in nature. Since then, progress has been rapid, with many fundamental discoveries made within the past two years. Here, we review our theoretical and experimental contributions to this effort.