Broken Time Reversal of Light Interaction with Planar Chiral Nanostructures

We report unambiguous experimental evidence of broken time-reversal symmetry for the interaction of light with an artificial nonmagnetic material. Polarized color images of planar chiral gold-on-silicon nanostructures consisting of arrays of gammadions show intriguing and unusual symmetry: structures, which are geometrically mirror images, lose their mirror symmetry in polarized light. The symmetry of images can be described only in terms of antisymmetry (black-and-white symmetry) appropriate to a time-odd process. The effect results from a transverse chiral nonlocal electromagnetic response of the structure and has some striking resemblance with the expected features of light scattering on anyon matter.

Figure 1

Intriguing color symmetry of images of metallic planar chiral structures taken in polarized light (a, d, e, h, i, m–u). Grayscale images b, c, f, g, k, l were taken in unpolarized light to show the underlying topography of the adjacent images. All images are $30\mu \mathrm{m}\times 30\mu \mathrm{m}$ apart from image u, which is $20\mu \mathrm{m}\times 20\mu \mathrm{m}$.

Figure 2

An electromagnetic wave interacting with a generic planar chiral object (scenario A), and symmetry transformations: (B) Time reversal, $\mathit{T}$; (C) Enantiomeric transformation of the sample, $\mathit{R}$; (D) Enantiomeric time reversal, $\mathit{R}\mathit{T}$. Boxed part on the right: The upper row shows the topography of the planar chiral object, as it appears when observed from the direction of light propagation, while the lower row shows simplified color patterns for the corresponding polarized images.

Figure 3

Electromagnetic fields of surface plasmon-polariton waves and volume waves with wave vectors $k_{\perp }$ and parallel $k_{\parallel }$ to the plane of the structure in two enantiomeric forms of the gammadion branch show no mirror symmetry. (○) represents field vector directed out of the plane of the picture; (●) represents field vector into the plane of the picture.