  The plasmonic chirality has drawn a lot of attention because of the tunable
circular dichroism (CD) and the enhancement for the signal of chiral molecules.
Different mechanisms have been proposed for explaining the plasmonic CD,
however, a quantitative one like ab initio mechanism in chiral molecules is
still unavailable. In this work, a mechanism similar to the chiral molecules is
analyzed. The giant extrinsic circular dichroism of plasmonic splitting
rectangle ring is quantitatively investigated theoretically. The interplay of
electric and magnetic modes of the meta-structure is proposed to explain the
giant CD. The interplay is analyzed both in an analytical coupled
electric-magnetic dipoles model and finite element method model. The surface
charge distributions show that the circular current yielded in the splitting
rectangle ring makes it behave like a magneton at some resonant modes, which
interact with electric modes and results in a mixing of the two kinds of modes.
The strong interplay of the two kinds of modes is mainly responsible for the
giant CD.The analysis of the chiral near field of the structure shows potential
applications in chiral molecule sensing.
