Chirality arising from small defects in gold nanoparticle arrays

The symmetry of metal nanostructures may be broken by their overall features or small-scale defects. To separate the roles of these two mechanisms in chiral symmetry breaking, we prepare gold nanostructures with chirality occurring on different levels. Linear optical measurements reveal small chiral signatures, whereas the chiral responses from second-harmonic generation are enormous. The responses of all structures are remarkably similar, suggesting that uncontrollable defects play an important role in symmetry breaking.