Chiral coupling in gold nanodimers

Second-harmonic generation from T-shaped gold nanodimers with nanogaps has different efficiencies for left- and right-hand circularly polarized fundamental light. The difference arises from the chiral symmetry breaking of the dimers due to nonorthogonal mutual orientations of the horizontal and vertical bars of the T shape and depends on the gap size. Unexpectedly, the smallest gap with presumably the strongest coupling gives rise to only a small difference. All results can be explained by considering the distribution of the polarized local field in the structure.