The in-plane optical conductivity of Bi 2 Sr 2 CaCu 2 O 8+δ thin films with small carrier density (underdoped) up to large carrier density (overdoped) is analyzed with unprecedented accuracy. Integrating the conductivity up to increasingly higher energies points to the energy scale involved when the superfluid condensate builds up. In the underdoped sample, states extending up to 2 eV contribute to the superfluid. This anomalously large energy scale may be assigned to a change of in-plane kinetic energy at the superconducting transition, and is compatible with an electronic pairing mechanism. 74.25.Gz, 74.72.Hs Typeset using REVT E X

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Single phase, c-axis oriented, e-doped, Sr 1-x La x CuO 2 thin films were epitaxially grown on KTaO 3 and DyScO 3 substrates by reactive rf sputtering. As-grown films being insulating due to oxygen excess, oxygen reduction is necessary to observe superconductivity. Two different procedures were employed to reach superconductivity.On one hand an in-situ reduction process was conducted on a series of films deposited on both types of substrates. On the other hand, an ex-situ reduction procedure was performed sequentially on a single film deposited on DyScO 3 . The study of the influence of oxygen reduction on the structural and electronic properties of the thin films is presented and discussed.

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We report a transport study down to 2 K and in high magnetic fields up to 20 T of a highly c-axis-oriented epitaxial thin film of electron-doped "infinite-layer" cuprate superconductor Sr 1−x La x CuO 2 with T c of 26 K. A 16 T magnetic field perpendicular to the ab plane of the film completely suppresses superconductivity, even at the lowest temperature. Perpendicular magnetic fields shift the resistive transition to lower temperatures, without significant broadening, in a way similar to that seen in conventional superconductors. The upper critical field H c2Ќ ͑T͒ exhibits an almost linear temperature dependence. It is shown that electron-doped infinite-layer cuprate presents three-dimensional superconductivity due to a weaker anisotropy ͑␥ =15͒ and smaller H c2Ќ ͑T͒ values than the ones of hole-doped cuprates.

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