Theory of fishnet negative-index optical metamaterials

We theoretically study fishnet metamaterials at optical frequencies. In contrast to earlier works, we provide a microscopic description by tracking the transversal and longitudinal flows of energy through the fishnet mesh composed of intersecting subwavelength plasmonic waveguides. The analysis is supported by a semi-analytical model based on surface-plasmon coupled-mode equations, which provides accurate formulas for the fishnet refractive index, including the real-negative and imaginary parts. The model simply explains how the surface plasmons couple at the waveguide intersections and it shines new light on the fishnet negative-index paradigm at optical frequencies. Extension of the theory for loss-compensated metamaterials with gain media is also presented.Comment: 4 figure

Bounded Gaps Between Products of Distinct Primes

Let $r \ge 2$ be an integer. We adapt the Maynard-Tao sieve to produce the asymptotically best-known bounded gaps between products of $r$ distinct primes. Our result applies to positive-density subsets of the primes that satisfy certain equidistribution conditions. This improves on the work of Thorne and Sono

Structural and electronic properties of ScnOm (n=1~3, m=1~2n) clusters: Theoretical study using screened hybrid density functional theory

The structural and electronic properties of small scandium oxide clusters ScnOm (n = 1 - 3, m = 1 - 2n) are systematically studied within the screened hybrid density functional theory. It is found that the ground states of these scandium oxide clusters can be obtained by the sequential oxidation of small "core" scandium clusters. The fragmentation analysis demonstrates that the ScO, Sc2O2, Sc2O3, Sc3O3, and Sc3O4 clusters are especially stable. Strong hybridizations between O-2p and Sc-3d orbitals are found to be the most significant character around the Fermi level. In comparison with standard density functional theory calculations, we find that the screened hybrid density functional theory can correct the wrong symmetries and yield more precise description for the localized 3d electronic states of scandium.Comment: 8 figure

Resonant versus anti-resonant tunneling at carbon nanotube A-B-A heterostructures

Narrow antiresonances going to zero transmission are found to occur for general (2n,0)(n,n)(2n,0) carbon nanotube heterostructures, whereas the complementary configuration, (n,n)(2n,0)(n,n), displays simple resonant tunneling behaviour. We compute examples for different cases, and give a simple explanation for the appearance of antiresonances in one case but not in the other. Conditions and ranges for the occurence of these different behaviors are stated. The phenomenon of anti-resonant tunneling, which has passed unnoticed in previous studies of nanotube heterostructures, adds up to the rich set of behaviors available to nanotube based quantum effect devices.Comment: Published in phys. stat. sol. (b); 6 pages, 4 figure