Paul M. Mankiewich

High-T/sub c/ superconductive delay line structures, and signal conditioning networks

The design and fabrication of high-T/sub c/ chirp-response tapped delay line filters are discussed. The key components in this development were long delay lines with more than 10 ns of delay, impedance transformers, and backward-wave couplers. All of the typical transmission line geometries were examined, including microstrip, coplanar and stripline. Designs were developed using microwave CAD routines and superconducting niobium delay line prototypes. Tapped delay line chirp filters with up to 12 ns of total delay have been successfully fabricated in YBaCuO.

High‐temperature dc superconducting quantum interference device with deep‐submicron YBa2Cu3O7 weak links

We have fabricated a YBa2Cu3O7 (YBCO) thin‐film dc superconducting quantum interference device (SQUID) with lithographically defined deep‐submicron weak links. At 77 K the voltage response to dc flux is sinusoidal and nonhysteretic, with maximum peak‐to‐peak amplitude of 5 μV. The maximum response is 8 μV at 70 K, where 2LI0/Φ0≊1. At lower temperatures, the maximum response oscillates in the range 4–6 μV. Random telegraph noise was observed near 30–40 K. Well‐behaved Shapiro steps were observable at all measured temperatures below Tc.

Fermi surface and critical field of YBCO

Abstract We have measured extremal areas of the Fermi surface of YBa2Cu3O6.97 by the de Haas-van Alphen effect and the superconducting critical field Hc2(T) by resistence measurements on epitaxial thin of films YBa2Cu3O7 (both called YBCO). Magnetic fields up to 140T were used in flux compression experiments. We have tentatively identified another piece of the Fermi surface with an area of 22kT, which is larger than expected. By both the de Haas-van Alphen effect and the resistance measurements, Hc2 with the applied magnetic field H parallel to the c axis of the YBCO is near 130 T. For H perpendicular to the c axis Hc2 is of the order of 900 T.

Switching noise in YBa/sub 2/Cu/sub 3/O/sub x/ 'macrobridges'

Intermittent switching was observed in the voltage current characteristics of thin-film bridges of YBa/sub 2/Cu/sub 3/O/sub x/. At a fixed bias point there are multiple metastable voltage states with lifetimes which depend on the bias current and applied magnetic field. The microbridges are made of thin ( >

Etching and annealing of substrates for superconducting multilayers and devices

The structural and electrical quality of YBa/sub 2/Cu/sub 3/O/sub 7- delta / grown on ion-etched substrates by a variety of techniques was investigated. Co-evaporated YBa/sub 2/Cu/sub 3/O/sub 7- delta / films deposited and postannealed on etched LaAlO/sub 3/ substrates have substantially higher room-temperature resistivities and wider c-axis rocking curve widths than films on unetched substrates. Annealing of the etched substrate prior to evaporation narrows the c-axis rocking curve width and restores resistivity and critical current densities to values comparable to those of the unetched controls. Laser-ablated films on etched substrates show a smaller absolute magnitude of rocking curve broadening and no change in DC electrical properties. An increase of the inhomogeneous strain was also observed in coevaporated postannealed and laser-ablated films on etched substrates.<<ETX>>

Low-temperature critical field of YBCO

We have measured the upper critical fieldHC2(T) of YBa2Cu3O7 (YBCO) thin films in magnetic fields up to 140 T forH applied parallel to thec-axis of the film. The critical field in the zero-temperature limit is 138 T, and the temperature dependence does not fit any simple model.

Two-GHz microstrip thin-film resonators of Nb and YBa/sub 2/Cu/sub 3/O/sub 7/

Dissipation and phase noise have been measured for 2-GHz linear microstrip resonators on 0.5-mm LaAlO/sub 3/. Fifty-ohm YBCO resonators with Nb ground planes (YBCO/Nb) showed quality factors of approximately 100,000 at 2 GHz and 4.2 K, somewhat less than measured in all-Nb resonators of the same geometry. The corresponding surface resistance of 10 microhms was maintained to average current densities of 1 MA/cm/sup 2/. All-YBCO resonators were measured to higher temperatures, and showed significant excess dissipation above about 60 K. The normalized phase noise of S/sub y/=-20/spl plusmn/2 was maintained to at least 30 K. This resonator was also operated in a resonator-stabilized oscillator configuration. The effect of package interactions on microstrip devices was also investigated.<<ETX>>