Generation of Hot Electrons with Chiral Metamaterial Perfect Absorbers: Giant Optical Chirality for Polarization-Sensitive Photochemistry

Abstract

Chiral plasmonic metamaterials have shown very interesting possibilities as chiral optical absorbers for circularly polarized light detection, as their optical response can be manipulated through the careful design of their geometry. Exhibiting the generation of hot electrons, chiral plasmonic nanostructures can be potentially used for polarization-sensitive photochemistry and chiral photocatalysis, in which the excited hot electrons induce surface reactions. In this study, we show that chiral metamaterial perfect absorbers (MMPAs) can be utilized for plasmon-induced polarization-sensitive photochemistry involving hot electrons, with extremely strong differential chiral responses. The calculated nearly perfect optical absorption (∼98%) of metamaterials demonstrate that the MMPAs can strongly absorb the photons and direct a significant part of the radiant energy to the generation of energetic (hot) carriers. Through the elaborate design of the plasmonic antenna geometry, we theoretically present a MMPA exhibiting a very large circular dichroism in its optical response. In addition, the greatly asymmetric electromagnetic field enhancement response of the MMPA to left and right circularly polarized light leads to a large chiral effect in the hot electron generation. In our calculations with the optimized designs, the g-factor reaches a value of 1.52, close to the theoretical upper limit of 2, higher than that of chiral colloidal nanocrystals with plasmonic resonances and much higher than for any chiral molecules. The remarkably strong chiral effect in hot electron generation, predicted in our study, suggests that plasmonic MMPAs can be used in polarization-sensitive photochemical applications and for photodetection.