  We report scanning tunneling microscopy investigation on epitaxial ultrathin
films of pyrite-type copper disulfide. Layer by layer growth of CuS2 films with
a preferential orientation of (111) on SrTiO3(001) and Bi2Sr2CaCu2O8+{\delta}
substrates is achieved by molecular beam epitaxy growth. For ultrathin films on
both kinds of substrates, we observed symmetric tunneling gap around Fermi
level that persists up to ~ 15 K. The tunneling gap degrades with either
increasing temperature or increasing thickness, suggesting new matter states at
the extreme two dimensional limit.
