Properties of epitaxial YBa2Cu3O7 thin films on Al2O3 {1̄012}

Abstract

Epitaxial YBa₂Cu₃O₇ films were grown on Al₂O₃ {1̄012} by a laser ablation technique. X‐ray diffraction shows that films are epitaxial with the c axis perpendicular to the substrate surface and ‘‘123’’ [110] aligned with sapphire [101̄1], although the full width at half maximum of the rocking curve is larger than those of epitaxial films on SrTiO₃. Typical T_c’s are between 85 and 88 K with transition widths between 0.5 and 3 K. The normal‐state resistivity is 270 μΩ cm at 300 K and extrapolates to zero at zero temperature while the magnetization J_c is as high as 5×10⁶ A/cm² at 4.2 K. High‐frequency loss measurements show that 2000‐Å‐thick epitaxial films on Al₂O₃ {1̄012} have a surface impedance about 1 mΩ at 13 GHz at 4.2 K.