Atsuki Inoue

Y–Ba–Cu–O/Nb Tunnel Type Josephson Junctions

Y-Ba-Cu-O/Au/AlOx/Nb tunnel type Josephson junctions were fabricated and their current-voltage relation exhibited typical characteristics of Josephson tunnel junctions such as supercurrent, hysteresis and rf-induced voltage steps at 4.2 K.

Y-Ba-Cu-O/AlOx/Nb Josephson Tunnel Junctions

We have fabricated Y-Ba-Cu-O/AlOx/Nb Josephson tunnel junctions using electron-beam evaporation of Al and Nb films and natural oxidation. Superconducting Josephson current, hysteresis, and rf-induced voltage steps at a voltage greater than 0.4 mV have been clearly observed at 4.2 K. Moreover, rf-induced subharmonic steps have appeared. Magnetic field dependence of the superconducting Josephson current has also been studied.

Nb/AlOx/Nb Josephson tunnel junctions using electron beam evaporation

Niobium/aluminum-oxide/niobium Josephson tunnel junctions have been fabricated using electron beam evaporation to form all-metal films in a high vacuum system. A quality factor, Vm (the product of the maximum dc Josephson current and the subgap resistance defined at 2 mV) between 36–37 mV, has been obtained for the best junctions of a 6 nm-thick Al layer by cooling down the surface of the base electrode for 100 minutes under a high background pressure, before the deposition of aluminum, after the formation of the base niobium electrode. An array of 80 series-connected junctions has also been fabricated using the selective niobium anodization process and the planarization process. The current-voltage characteristics of the array showed a standard deviation of the maximum dc Josephson current of 3.3%.

Y-Ba-Cu-O/Nb Josephson tunnel junctions

The authors fabricated Y-Ba-Cu-O/Au/AlO/sub x//Nb and Y-Ba-Cu-O/AlO/sub x//Nb Josephson tunnel junctions using electron-beam evaporation of Al and Nb films and natural oxidation. Sintered Y-Ba-Cu-O was used as the base electrode. Superconducting Josephson current and hysteresis of the current-voltage characteristics, which are typical features of Josephson tunnel junctions, have been observed at 4.2 K. RF-induced voltage steps at a voltage greater than 0.4 mV have been clearly observed, and RF-induced subharmonic steps have also appeared. The superconducting Josephson current was modulated by the magnetic field. >

Interaction of La-Sr-Cu-0 and Ln-Ba-Cu-O (Ln= Y, Ho, Yb) Films With Ceramic Substrates

In the preparation of superconducting oxide films, one frequently observes crack formation, crystal orientation, phase seperation, and chemical reaction, all of which involve interactions between superconductors and substrate. Quantitative verification of these phenomena is expected to provide useful information for the preparation and microprocessing of high Tc films. Thermal expansion behavior of representative superconductors and substrate materials has been measured by a dilatometric method. The superconductors have far greater mean thermal expansion coefficients than conventional substrate materials and the difference correspond well with the crack size observed in some of the films. The non-linear expansion of BLnCO also contain information on the kinetics of oxygen uptake and secession as well as on the phase transition temperature. The effect of lattice matching has been investigated on Ba-Yb-Cu-O films. The films were deposited by sputtering on (100) and (110) SrTiO3 and some other ceramic substrates and their orientation was measured by SEM. Furthermore, chemical interaction has been examined by heating mixed powders of superconductors and substrate materials at various temperatures. The structural variation and the reduction in superconducting volume fraction were analyzed by X-ray diffraction and ac-susceptibility measurements, respectively.