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Quantitative Study on Circular Dichroism Induction from Chiral Matter-Achiral Nanostructure Near Field Interactions

The circular dichroism (ICD) induced from interaction of chiral molecules with achiral plasmonic metal nanostructures has improved sensitivity of molecular chirality detection. Although experimental results have presented several orders magnitude of ICD enhancement, but the cause of ICD induction has not arise from previous studies. In this paper, a theory presented for explain mechanism of ICD induction from near field interaction of chiral molecule with achiral nanostructure. By introducing dipole approaching of chiral molecule and a near field approximation of molecule-nanostructure interaction, we derived an analytical formula for ICD. This theory explains mechanism of ICD is that the dipole radiation of chiral molecules breaks the enantiomorphic relationship of the electric field strengths in the nanostructure. Furthermore, the derived formula exhibits ICD proportional to molecules chirality parameter and number density, and it exponentially increases with the inverse cube of distance between molecule and nanostructure. Most importantly, the formula shows that ICD is proportional to strengths of electric field in nanostructure and magnetic field in molecular region. To verify the analytical results, we studied the ICD properties of graphene nanohole metasurface (GNM) and chiral molecule composed system. Numerical results were found consistent with analytical results. Our investigation results are helpful for understanding mechanism of ICD induction, pushing the limit of ICD enhancement and realizing supersensitive detection of molecular chirality.