ELECTROMAGNETIC SPIN CURRENT DENSITY OF SURFACE PLASMON POLARITONS

A subject of plasmonic spinphotonics is developed for surface plasmon polaritons (SPPs). Since an electromagnetic field is a vectorial field, it has spinning angular momentum, and thus spin current is one of its degrees of freedom. A spin current density tensor has 24 independent components because of its antisymmetry in coordinate indices. By using the law of conservation of electromagnetic angular momentum (i.e., orbital angular momentum plus spinning angular momentum), the electromagnetic spin current density tensor is derived, and its characteristics are indicated. Since surface plasmon polaritons can exhibit various intriguing optical and electromagnetic effects and have many practical applications, we consider a new potential effect relevant to spin current transfer. The electromagnetic spin current density tensor and its intensity profile are analyzed for SPPs sustained on a metal-dielectric interface. The plasmonic spin on a metal ring and a straight thin metal belt is calculated, and based on this, a nanomechanical effect caused by plasmonic spin current transfer is suggested. It is expected that such a nontrivial nanomechanical effect will be useful in the design of new nanophotonic devices aiming at sensitive, accurate measurement techniques.