  The development of new nanophotonic devices requires the understanding and
modulation of the propagating surface plasmon and phonon modes arising in
plasmonic and polar dielectric materials, respectively. Here we explore the
CdZnO alloy as a plasmonic material, with a tunable plasma frequency and
reduced losses compared to pure CdO. By means of attenuated total reflectance,
we experimentally observe the hybridization of the surface plasmon polariton
(SPP) with the surface phonon polariton (SPhP) in the air-CdZnO-sapphire
three-layer system. We show how through the precise control of the CdZnO
thickness, the resonance frequencies of the hybrid surface plasmon-phonon
polariton (SPPP) are tuned in the mid-infrared, and the nature of the hybrid
mode turns from a plasmon-like behavior in the thicker films to a phonon-like
behavior in the thinnest films. The presence of sapphire phonons not only
allows the hybrid mode to be formed, but also improves its characteristics with
respect to the bare SPP. The reduced damping of the phonon oscillators allows
to reduce the losses of the hybrid mode, enhancing the propagation length above
500 microns, one order of magnitude larger than that of typical SPPs, clearing
the path for its application on emerging devices such as plasmonic waveguides.

Applied Physics