title: A single-layer wide-angle negative-index metamaterial at visible frequencies.
abstract: Metamaterials are materials with artificial electromagnetic properties defined by their sub-wavelength structure rather than their chemical composition. Negative-index materials (NIMs) are a special class of metamaterials characterized by an effective negative index that gives rise to such unusual wave behaviour as backwards phase propagation and negative refraction. These extraordinary properties lead to many interesting functions such as sub-diffraction imaging and invisibility cloaking. So far, NIMs have been realized through layering of resonant structures, such as split-ring resonators, and have been demonstrated at microwave to infrared frequencies over a narrow range of angles-of-incidence and polarization. However, resonant-element NIM designs suffer from the limitations of not being scalable to operate at visible frequencies because of intrinsic fabrication limitations, require multiple functional layers to achieve strong scattering and have refractive indices that are highly dependent on angle of incidence and polarization. Here we report a metamaterial composed of a single layer of coupled plasmonic coaxial waveguides that exhibits an effective refractive index of -2 in the blue spectral region with a figure-of-merit larger than 8. The resulting NIM refractive index is insensitive to both polarization and angle-of-incidence over a +/-50 degree angular range, yielding a wide-angle NIM at visible frequencies.
authors.affiliation: Kavli Nanoscience Institute, California Institute of Technology, MS 128-95, Pasadena, California 91125, USA.
authors.forename: Stanley P
authors.initials: SP
authors.lastname: Burgos
authors.forename: Rene
authors.initials: R
authors.lastname: de Waele
authors.forename: Albert
authors.initials: A
authors.lastname: Polman
authors.forename: Harry A
authors.initials: HA
authors.lastname: Atwater
references.citation: Opt Express. 2008 Nov 10;16(23):19001-17
references.pmid: 19581993
references.citation: Opt Lett. 2005 Dec 15;30(24):3356-8
references.pmid: 16389830
references.citation: Opt Lett. 2007 Jan 1;32(1):53-5
references.pmid: 17167581
references.citation: Science. 2001 Apr 6;292(5514):77-9
references.pmid: 11292865
references.citation: Phys Rev Lett. 2005 Sep 23;95(13):137404
references.pmid: 16197179
references.citation: Phys Rev E Stat Nonlin Soft Matter Phys. 2005 Mar;71(3 Pt 2B):036617
references.pmid: 15903615
references.citation: Phys Rev E Stat Phys Plasmas Fluids Relat Interdiscip Topics. 1994 Nov;50(5):4094-4106
references.pmid: 9962466
references.citation: Phys Rev Lett. 2000 Oct 30;85(18):3966-9
references.pmid: 11041972
references.citation: Science. 2005 Apr 22;308(5721):534-7
references.pmid: 15845849
references.citation: Nano Lett. 2009 Aug;9(8):2832-7
references.pmid: 19603794
references.citation: Phys Rev Lett. 2003 Mar 14;90(10):107401
references.pmid: 12689029
references.citation: Opt Express. 2008 Mar 31;16(7):4785-96
references.pmid: 18542577
references.citation: Opt Express. 2008 Sep 29;16(20):15439-48
references.pmid: 18825180
references.citation: Science. 2007 Jan 5;315(5808):47-9
references.pmid: 17204630
references.citation: Opt Lett. 2007 Jun 15;32(12):1671-3
references.pmid: 17572742
references.citation: Science. 2006 Jun 23;312(5781):1780-2
references.pmid: 16728597
references.citation: Science. 2009 Jan 16;323(5912):366-9
references.pmid: 19150842
references.citation: Science. 2007 Apr 20;316(5823):430-2
references.pmid: 17379773
references.citation: Nature. 2008 Sep 18;455(7211):376-9
references.pmid: 18690249
references.citation: Phys Rev Lett. 2008 Mar 21;100(11):113901
references.pmid: 18517786
references.citation: Opt Lett. 2007 Mar 1;32(5):551-3
references.pmid: 17392918
references.citation: Phys Rev Lett. 2000 May 1;84(18):4184-7
references.pmid: 10990641
references.citation: Science. 2006 May 12;312(5775):892-4
references.pmid: 16690860