  Near-infrared epsilon-near-zero (ENZ) metamaterial slabs based on
silver-germanium (Ag-Ge) multilayers are experimentally demonstrated.
Transmission, reflection and absorption spectra are characterized and used to
determine the complex refractive indices and the effective permittivities of
the ENZ metamaterial slabs, which match the results obtained from both the
numerical simulations and the optical nonlocalities analysis. A rapid
post-annealing process is used to reduce the collision frequency of silver and
therefore decrease the optical absorption loss of multilayer metamaterial
slabs. Furthermore, multilayer grating structures are studied to enhance the
optical transmission and also tune the location of ENZ wavelength. The
demonstrated near-infrared ENZ multilayer metamaterial slabs are important for
realizing many exotic applications, such as phase front shaping and engineering
of photonic density of states.
