MgB₂ superconducting thin films with a transition temperature of 39 kelvin

We fabricated high-quality c axis-oriented epitaxial MgB₂ thin films using a pulsed laser deposition technique. The thin films grown on (1 1̄ 0 2) Al₂O₃ substrates have a transition temperature of 39 kelvin. The critical current density in zero field is ∼6 × 10⁶ amperes per cubic centimeter at 5 kelvin and ∼3 × 10⁵ amperes per cubic centimeter at 35 kelvin, which suggests that this compound has potential for electronic device applications, such as microwave devices and superconducting quantum interference devices. For the films deposited on Al₂O₃, x-ray diffraction patterns indicate a highly c axis-oriented crystal structure perpendicular to the substrate surface.