  Controlling low power light beam self-confinement with ultrafast response
time opens up opportunities for the development of signal processing in
microdevices. The combination of highly nonlinear medium with the tight
confinement of plasmonic waves offers a viable but challenging configuration to
reach this goal. Here, we report the experimental observation of
plasmon-soliton waves propagating in a chalcogenide-based four-layer planar
geometry engineered to limit plasmon propagation losses while exhibiting
efficient Kerr self-focusing at moderate power. The observations reveal a
strongly enhanced self-focusing undergone by a self-trapped beam propagating
inside the structure. As expected, only TM polarized waves exhibit such a
behavior. Different experimental arrangements are tested that unambiguously
reveal the nonlinear plasmon-soliton coupling which is corroborated by
numerical simulations.
