title: Symmetry breaking and optical negative index of closed nanorings.
abstract: Metamaterials have extraordinary abilities, such as imaging beyond the diffraction limit and invisibility. Many metamaterials are based on split-ring structures, however, like atomic orbital currents, it has long been believed that closed rings cannot produce negative refractive index. Here we report a low-loss and polarization-independent negative-index metamaterial made solely of closed metallic nanorings. Using symmetry breaking that negatively couples the discrete nanorings, we measured negative phase delay in our composite 'chess metamaterial'. The formation of an ultra-broad Fano-resonance-induced optical negative-index band, spanning wavelengths from 1.3 to 2.3 μm, is experimentally observed in this structure. This discrete and mono-particle negative-index approach opens exciting avenues towards symmetry-controlled topological nanophotonics with on-demand linear and nonlinear responses.
authors.affiliation: NSF Nanoscale Science and Engineering Centre, 3112 Etcheverry Hall, University of California, Berkeley, California 94720, USA.
authors.forename: Boubacar
authors.initials: B
authors.lastname: Kanté
authors.forename: Yong-Shik
authors.initials: YS
authors.lastname: Park
authors.forename: Kevin
authors.initials: K
authors.lastname: O'Brien
authors.forename: Daniel
authors.initials: D
authors.lastname: Shuldman
authors.forename: Norberto D
authors.initials: ND
authors.lastname: Lanzillotti-Kimura
authors.forename: Zi
authors.initials: Z
authors.lastname: Jing Wong
authors.forename: Xiaobo
authors.initials: X
authors.lastname: Yin
authors.forename: Xiang
authors.initials: X
authors.lastname: Zhang