Surface plasmon polaritons (SPP) are composite electromagnetic field-charge density wave collective modes that propagate at metal/dielectric interfaces at the local speed of light. The circulation of their fields from transverse to longitudinal causes a transverse spin angular momentum (SAM) locking known as quantum spin-Hall effect, which embodies the property of evanescent waves, such as SPPs, that changing the sign of the photon momentum direction changes the sign of its spin. In other words, the oppositely propagating SPP waves possess the opposite spin. SPP fields can also carry optical angular momentum (OAM), which can focus them into plasmonic vortices. [more]