Preparation and Electronic Properties of YBa₂Cu₃O_xFilms with Controlled Oxygen Stoichiometries

Abstract

We describe a novel technique capable of controlling the oxygen content of YBa 2 Cu 3 O x (YBCO) films in a precise and reversible manner. The temperature dependence of resistivity and the distinct two-plateau behavior in critical temperature T co versus oxygen content plot of these films are consistent with those observed in the bulk and single crystals of YBCO. The O 1 s and Cu 2 p absorption spectra of these films were measured by polarization-dependent X-ray absorption spectroscopy (XAS). The intensity variations of the pre-edge peaks as a function of oxygen content are discussed. We also used these films to systematically study the electron-phonon coupling strength and the position of Fermi level by using a femtosecond pump-probe technique. A clear sign-reversal of the transient reflectivity, which was consistently explained by the thermomodulation model, was observed. Both of these optical measurements support the idea that the electronic structure of YBCO cuprates is based on the charge transfer model with hybridization between the Cu and O sites.