We fabricate and characterize a metal-dielectric nanostructure with an effective refractive index n=0 in the visible spectral range. Light is excited in the material at deep subwavelength resolution by a 30-keV electron beam. From the measured spatially- and angle-resolved emission patterns a vanishing phase advance, corresponding to an effective e = 0 and n=0, is directly observed at the cutoff frequency. The wavelength at which this condition is observed can be tuned over the entire visible/near-infrared spectral range by varying the waveguide width. This n=0 plasmonic nanostructure may serve as a new building block in nanoscale optical integrated circuits and to control spontaneous emission as experimentally demonstrated by the strongly enhanced radiative optical density of states over the entire n=0 structure.

Selected as a Viewpoint in: Physics 6(2013)1, DOI:10.1103/Physics.6.1

Highlighted in:
Science 338, 727 (2012) and Nature 493, 143 (2013)

Phys. Rev. Lett.
Photonic Materials

Vesseur, E. J. R., Coenen, T., Caglayan, H., Engheta, N., & Polman, A. (2013). Experimental verification of n=0 structures for visible light. Phys.Rev.Lett., 110(01, Article number: 13902), 1–5. doi:10.1103/PhysRevLett.110.013902