Plasmon-Mediated Chiroptical Second Harmonic Generation from Seemingly Achiral Gold Nanorods

Throughout nature,simple rules explain complex phenomena, suchas the selective interaction of chiral objects with circularly polarizedlight. Here, we demonstrate chiroptical signals from gold nanorods,which are seemingly achiral structures. Shape anisotropy due to atomic-levelfaceting and rounding at the tips of nanorods, which are free of chiralsurface ligands, induces linear-to-circular polarization modulationduring second harmonic generation. The intrinsic nanorod chiropticalresponse is increased by plasmon-resonant excitation, which preferentiallyamplifies circularly polarized harmonic signals. This structure-plasmoninterplay is uniquely resolved by polarization-resolved second harmonicgeneration measurements. The material's second-order polarizabilityis the product of the structure-dependent lattice-normal susceptibilityand local surface plasmon field vectors. Synthetically scalable plasmon-supportingnanorods that amplify small circular dichroism signals provide a simple,assembly-free platform for chiroptical transduction.