  We have derived a dispersion relation governing the surface plasmon resonance
established along a planar interface between a metal and a chiral medium
(chiral case). Resulting numerical solutions are compared with the well-known
results obtained for a metal-dielectric interface (achiral case). Comparisons
show that the chiral case exhibits smaller phase speeds than the achiral case.
Such a longitudinal deceleration in the chiral case is caused by the energy
expended on establishing the longitudinal spin density, which turns out
anti-symmetric with respect to medium chirality. Moreover, the low-frequency
range is disallowed in the chiral case. Relevant energy redistributions,
spin-orbital couplings, and applications are discussed.
