OXYGEN-INDUCED SUPERCONDUCTING, METALLIC OR INSULATING BEHAVIOR IN AS-GROWN EPITAXIAL BI2SR2CUOX THIN-FILMS

Epitaxial Bi2Sr2CuOx thin films were prepared in situ by reactive RF magnetron sputtering. Superconducting films with T(c)(R=0) up to 18 K were obtained which correspond to what we call an optimal oxygen content. It is the highest T(c) reported for films of the 2201 phase. In the case of films made under the same sputtering conditions, the superconducting critical temperature value decreases and superconductivity disappears when the oxygen content in the films is decreased or increased during the cooling process. With reference to the optimal oxygen content, overdoped films tend to display a normal metal behaviour and underdoped films tend to display a semiconductor-like behaviour at low temperature.