Switchable Chiroptical Hot-Spots in Silicon Nanodisk Dimers

We demonstrate uniform sign optical chirality generation in dimers of silicon (Si) nanodisks under linear light polarization through combination of experimental spectroscopy and electromagnetic simulations. Excitation of the magnetic dipole resonance in individual Si nanodisks generates enhanced electric and magnetic fields. We show that the fields provided by adjacent Si nanodisks excited with linearly polarized light at the magnetic dipole resonance can align to generate strong near-field chirality in the gap between the Si nanodisks. The near-field chirality enhancement for Si nanodisk dimers is compared with that for resonant gold (Au) nanoparticle dimers that provide almost exclusively electric field enhancement. We experimentally determine the third Stokes parameter, S3, of light transmitted through Si nanodisk dimers fabricated on sapphire as a measure for the chirality flux and the related near-field chirality. The experiments confirm the generation of uniform sign optical chirality in the Si nanodisk dimers whose handedness can be switched through choice of the orientation of the incident linear light polarization and whose amplitude decreases with increasing gap separation.