  Gallium metallic photonic crystals with 100% filling factor have been
fabricated via infiltration of liquid gallium into opals of 300-nm silica
spheres using a novel high pressure-high temperature technique. The electrical
resistance of the Ga-opal crystals was measured at temperatures from 10 to 280
K. The data obtained show that Ga-opal crystals are metallic network with
slightly smaller temperature coefficient of resistivity than that for bulk
gallium. Optical reflectivity of bulk gallium, plain opal and several Ga-opal
crystals were measured at photon energies from 0.3 to 6 eV. A pronounced
photonic stop band in the visible spectral range was found in both the plain
and Ga infiltrated opals. The reflectivity spectra also show increase in
reflectivity below 0.6 eV; which we interpret as a significantly lower
effective plasma frequency of the metallic mesh in the infiltrated opal compare
to the plasma frequency in the pure metal.
