Role of magnetic induction currents in nanoslit excitation of surface plasmon polaritons.

We present a method for exciting surface plasmon polaritons (SPPs) caused by a magnetic field component perpendicular to the direction of slit. The excitation mechanism is based on the spatially oscillating induced current along the edges of the slit under obliquely incident electromagnetic waves. Our finding distinguishes itself from previous mechanisms based on transverse electric fields and unveils the missing point of the SPP-excitation problem in a nanoslit. The use of a magnetic field for SPP excitation can be highly efficient and even comparable to that with an electric field, so that their composition can lead to selective unidirectional excitation.