A perovskite-like single-crystal substrate material has been investigated that simultaneously permits epitaxial growth of 1-2-3 superconductor films and possesses desirable rf properties of low dielectric constant and loss tangent. The lattice constant of 3.792 Å provides a lattice match to within 1% of the a axis of 1-2-3. Sputtered films of erbium-barium-copper-oxide have been produced on (100) LaAlO3 substrates that exhibit sharp resistive transitions at 90 K (ΔT=1K), bulk superconductivity as determined by ac susceptibility measurements, and nearly single-crystal growth as evidenced by x-ray diffraction and high-resolution scanning electron microscopy. The high-frequency dielectric properties of LaAlO3 were experimentally investigated at several temperatures. The low-frequency dielectric constant was measured to be 15 and the microwave loss tangent ranged from 6×10−4 at room temperature to 5×10−6 at 4 K.

We have grown crystalline thin films of LaAlO3 using off-axis rf sputtering from a single stoichiometric target. The films grow epitaxially on SrTiO3 and LaAlO3  (100) substrates as well as on YBa2Cu3O7 thin films. We report on the growth conditions used to make these films, the properties of the films, and the properties of bilayer and trilayer structures containing both LaAlO3 and YBa2Cu3O7 films. Transmission electron microscopy cross-sectional and x-ray diffraction analyses indicate that all the constituent films in the multilayers grow epitaxially and that the interfaces between the films are sharply defined. Preliminary transport measurements on these multilayers show that LaAlO3 can be used for dielectric layers in a variety of high-temperature superconductor electronic circuits.

We have developed a technique which permits high-yield fabrication of microbridges and low noise YBa2Cu3O7 superconducting quantum interference devices (SQUIDs) in epitaxial thin films. These SQUIDs operate over a wide temperature range extending from 4 K to close to the superconducting transition temperature. Measurements of an rf SQUID operating at 77 K give a peak-to-peak flux sensitivity of 36 μV/Φ0 and a flux noise at 10 Hz of 1.5× 10−4 Φ0/√Hz. Device yields over 80% have been obtained.

The surface impedance of superconducting YBa2Cu3O7 films as a function of temperature at 10 GHz has been measured in a parallel plate resonator geometry. The penetration depth λ(T), complex microwave conductivity σ(T), and quasiparticle scattering rate 1/τ(T) were also determined. After a rapid fall as T is lowered below Tc, the surface resistance Rs exhibits a linear dependence from 65 K down to 6 K. As T drops below Tc, the real part of the conductivity σ1 has a rapid rise, which is attributed to the observed dramatic increase in τ. The normal-fluid density shows a linear behavior at low temperatures, which is inconsistent with s-wave BCS superconductivity.

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