The development of sputtering-magnetron techniques makes possible the manufacturing of thin-film coated rf cavities for high-energy accelerators of various superconducting alloys or compounds. In this context high-quality (Nb1-xTix)N films have been produced by dc magnetron sputtering and carefully characterized. These films, for xâ\u89¤0.5, exhibit a critical temperature Tc as high as NbN (Tc=17 K) but show a markedly lower normal state resistivity. The calculated BCS surface impedance of the films is also lower than for NbN. The overall properties of the (Nb1-xTix)N films are compared with those of other superconductors, and the suitability of this material for the production of superconducting sputter-coated copper cavities for particle physics accelerators is demonstrated. The potential interest of (Nb1-xTix)N films for superconducting electronics is also briefly outlined. © 1990 Plenum Publishing Corporation

We report a demonstration of S-I-S quasiparticle tunneling in c-axis oriented planar junctions consisting of YBaCuO͞PrBaCuO͞HoBaCuO thin film heterostructures. In the conductance curves at low temperatures well developed peaks indicative of gap structures are found at 645 mV. The high bias conductance shows flat dependence on energy and the best quality junction has a zero-bias conductance less than 0.05 of the normal state value. We discuss our spectra in the framework of a BCS-like density of states as well as in terms of a d x 2 2y 2 symmetry of the superconducting order parameter. PACS numbers: 74.50.+r, 74.80.Dm Tunneling studies in high-T c heterostructures composed of superconducting-insulating-superconducting ͑S-I-S͒ layers are of great interest from both a fundamental and a technological point of view. Junction characteristics in fact can provide important information on the quasiparticle density of states and on the mechanism responsible for superconductivity which still are open questions about high-T c superconductors (HTS). On the other hand, trilayers are the basic structure for high-frequency transmission lines, for filters, and for the realization of Josephson junctions for high-T c integrated circuits.Problems associated with multilayer structures arise from the insulating barriers and interfaces. Barrier materials need to have a close lattice match and compatible deposition conditions with the HTS in order to propagate epitaxial growth. Formation of good quality interfaces is also important. The roughness of the surfaces can produce the mixing of properties of different directions in these anisotropic materials. In addition, due to the extremely short coherence length j, the superconducting properties are easily degraded at the interfaces. To overcome this last difficulty, superconductor-normal-superconductor ͑S-N-S͒ junctions have been developed for Josephson devices, since, due to the proximity effect, they show Josephson coupling even if the metal barrier thickness is greater than j.Recently, different kinds of all-oxide S-N-S structures, including grain boundary, step edge, ramp-type, and sandwich-type junctions, have been realized by several groups for high-T c device applications. In particular, YBa 2 Cu 3 O 72d ͞PrBa 2 Cu 3 O 72d 0 ͞YBa 2 Cu 3 O 72d junctions have been investigated in detail by using a-axis oriented [1-3] and, more recently, (103)-oriented films [4].In contrast with the excellent results obtained in Josephson coupled S-N-S trilayers, clear evidence for quasiparticle tunneling is difficult to obtain in alloxide S-I-S junctions. Several attempts to realize HTS-I-HTS structures have been reported in the literature., and Bi 2 -Sr 2 CaCu 2 O 8 ͞Bi 2 Sr 2 YCu 2 O 8 ͞Bi 2 Sr 2 CaCu 2 O 8 junctions [8] have been measured. However, in all these structures, due to the difficulty of realization of good quality interfaces between the insulating barrier and the counterelectrodes, quasiparticle tunneling shows a S-I-N behavior with gaplike features developed well below the measured ...

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