Giant plasmonic circular dichroism in Ag staircase nanostructures.

We demonstrate large circular dichroism (CD) in the visible range resulting from electromagnetic couplings in three-dimensional Ag staircase nanostructures. Analytical calculations using effective constitutive parameters show that the CD originates from chiral resonances of the staircase in which the induced magnetic dipole moment has components parallel or antiparallel to the induced electric dipole moment. The strength of the coupling as well as the CD can be tuned by varying the configuration (e.g. the strip width) of staircase nanostructure. More importantly we are able to realize such chiral resonances with large CD in the visible range in topologically similar chiral nanostructures fabricated using a simple shadowing vapor deposition method. Our simple staircase model demonstrates the effect of couplings between electric and magnetic dipole moments in producing large chiral responses in 3D nanostructures and can enhance the understanding of hybrid chiral optical systems.