  Optical reflection measurements within the highly conducting (a,b)-plane of
the organic metal (BEDT-TTF)_4[Ni(dto)_2] reveal the gradual development of a
sharp feature at around 200 cm as the temperature is reduced below 150 K. Below
this frequency a narrow Drude-like response is observed which accounts for the
metallic behavior. Since de Haas-von Alphen oscillations at low temperatures
confirm band structure calculations of bands crossing the Fermi energy, we
assign the observed behavior to a two-dimensional metallic state in the
proximity of a correlation induced metal-insulator transition.
