title: Superconductivity in two-dimensional CoO2 layers.
abstract: Since the discovery of high-transition-temperature (high-T(c)) superconductivity in layered copper oxides, many researchers have searched for similar behaviour in other layered metal oxides involving 3d-transition metals, such as cobalt and nickel. Such attempts have so far failed, with the result that the copper oxide layer is thought to be essential for superconductivity. Here we report that Na(x)CoO2*yH2O (x approximately 0.35, y approximately 1.3) is a superconductor with a T(c) of about 5 K. This compound consists of two-dimensional CoO2 layers separated by a thick insulating layer of Na+ ions and H2O molecules. There is a marked resemblance in superconducting properties between the present material and high-T(c) copper oxides, suggesting that the two systems have similar underlying physics.
authors.affiliation: Advanced Materials Laboratory, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan. takada.kazunori@nims.go.jp
authors.forename: Kazunori
authors.initials: K
authors.lastname: Takada
authors.forename: Hiroya
authors.initials: H
authors.lastname: Sakurai
authors.forename: Eiji
authors.initials: E
authors.lastname: Takayama-Muromachi
authors.forename: Fujio
authors.initials: F
authors.lastname: Izumi
authors.forename: Ruben A
authors.initials: RA
authors.lastname: Dilanian
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Sasaki