We report the first observation of a magnetic dipolar contribution to the nonlinear optical
(NLO) response of colloidal metal nanostructures. Second-order NLO responses from
several individual solid gold nanosphere (SGN) dimers, which we prepared by a bottom-up
approach, were examined using polarization-resolved second harmonic generation (SHG)
spectroscopy at the single-particle level. Unambiguous circular dichroism in the SH signal
was observed for most of the dimeric colloids, indicating that the plasmon field located within …