Properties of epitaxial films of YBa₂Cu₃O_7-δ

We present measurements of the properties of epitaxial thin films of superconducting YBa₂Cu₃O_7-δ, with T_c about 90 K, transition widths of ∼2.5 K, and critical currents in excess of 10⁵A/cm² at 77 K. The temperature dependence of the upper critical field exceeds 4 T/K for fields parallel to the film (i.e., H⊥ to the c axis) and the anisotropy of the upper critical field ranged between two and three. Our tunneling gaps (Δ∼15-21 meV) are similar to previous results on ceramic and single-crystal samples of YBa₂Cu₃O_7-δ. Infrared measurements of the gap energy suggest a larger value than previous measurements on polycrystalline material. The temperature dependence of the Hall coefficient is similar to that for the bulk.