  Here we report the designing of chiral metamaterial with metallic helix
array. The effective electric and magnetic dipoles, which originate from the
induced surface electric current upon illumination of incident light, are
collinear at the resonant frequency. Consequently, for the circularly polarized
incident light, negative refractive index is realized. Our design provides a
unique approach to tune the optical properties by assembling helices, and
demonstrates a different approach in exploring three- dimensional chiral
metamaterial.
