Cut-offs and light-spin flips in surface plasmon resonance between a chiral medium and a metal

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.