Optical singularities associated with the energy flow of two closely spaced core-shell nanocylinders

Optical singularities associated with the energy flow of two closely spaced dielectric-core gold-shell nanocylinders are studied by two-dimensional finite difference time domain method. The simulation results show that optical vortices as well as saddle points can be observed in the energy flow pattern of light interacting with the core-shell nanocylinder pair in its in-phase symmetric dipolar plasmon mode. The rotating direction of the optical vortices can be tuned by varying the width of the gap between the nanocylinder pair and the value of the permittivity of the dielectric core.