Anisotropic propagation of surface plasmon polaritons caused by oriented molecular overlayer

We performed reverse attenuated total reflection measurements on 50-nm-thick Ag thin films coated with oriented sexithiophene molecular layers. The dispersion curves obtained clearly demonstrate that the wavevectors of surface plasmon polaritons propagating parallel to the molecular orientation have larger magnitudes than those propagating perpendicular to the molecular orientation. The results provide us with an approach to generate anisotropic propagation of surface plasmon polaritons simply controlled by the molecular orientation of an overlayer.