  Chiral structure can be applied to construct metamaterial with negative
refractive index (NRI). In an assembly of double-layered metallic U-shaped
resonators with two resonant frequencies wH and wL, the effective induced
electric and magnetic dipoles, which are contributed by the specific surface
current distributions, are collinear at the same frequency. Consequently, for
left circularly polarized light, NRI occurs at wH, whereas for right circularly
polarized light it occurs at wL. Our design provides a new example to apply
chiral structures to tune electromagnetic properties, and could be enlightening
in exploring chiral metamaterials.
