We present the blueprint for a novel negative-index metamaterial. This
structure is fabricated via three-dimensional two-photon direct laser writing
and silver shadow evaporation. The comparison of measured linear optical
spectra with theory shows good agreement and reveals a negative real part of
the refractive index at around 3.85 micrometer wavelength - despite the fact
that the metamaterial structure is bi-anisotropic due to the lack of inversion
symmetry along its surface normal.Comment: 8 pages, 3 figure