  Recently the new concepts of transverse spin angular momentum and Belinfante
spin momentum of evanescent waves have drawn considerable attention. Here, we
investigate these novel physical properties of electromagnetic fields in the
context of locally excited surface plasmon polaritons. We demonstrate, both
analytically and numerically, that locally excited surface plasmon polaritons
possess transverse spin angular momentum and Belinfante momentum with rich and
non-trivial characteristics. We also show that the transverse spin angular
momentum of locally excited surface plasmon polaritons leads to the emergence
of transverse chiral forces in opposite directions for chiral objects of
different handedness. The magnitude of such a transverse force is comparable to
the optical gradient force and scattering forces. This finding may pave the way
for realization of optical separation of chiral biomolecules.
