The dependences of critical current on the temperature and magnetic field and the current-voltage characteristics in response to incident microwave radiation are measured in the direction of the c-axis of the 80 K superconducting phase (Bi, Pb)2Sr2CaCu2Oy bulk single crystal. Josephson junctionlike behavior is successfully observed, and it shows that the single crystal itself is composed of Josephson junctions along the c-direction and that its electrical transport in this direction is limited by intrinsic tunnel barriers existing in the single crystal.

Single-crystal cubic NbNx films with thicknesses of a few thousand angstroms were epitaxially grown on cleaved (100) planes of single-crystal MgO plates by the vapor phase growth technique. By heat treatment of some of these films in NH3+H2 or in H2 alone, films having the superlattice structures of Nb4N3, NbN, or Nb4N5 were prepared. The maximum Tc was observed in cubic NbNx. Both Nb4N3 and Nb4N5, the tetragonal phases with long-range-ordered arrangement of vacancies, exhibited superconductivity. NbN1.0 and Nb5N6, both with hexagonal structure, did not exhibit superconductivity down to 1.77 K. As the composition of cubic NbNx became close to stoichiometric, its Tc increased. However, the maximum Tc of cubic NbNx with nearly stoichiometric composition was limited by the lattice instability of cubic NbNx and by the resulting cubic NbNx to hexagonal NbN transformation. It might be expected that a higher Tc for compounds of the NbN family could be obtained if a NaCl-type crystal with less vacancies could exist as a stable or metastable phase at ordinary temperatures.

We report the observation of the highest velocity mode of Josephson vortex motion in mesas consisting of 5–15 intrinsic Josephson junctions with an area of 37×30 μm2 on Bi2Sr2CaCu2Oy single crystals. By applying the dc magnetic field parallel to CuO2 planes in the mesas, resonant steps and flux flow branches have been observed on the current–voltage characteristics along the c-axis of the mesas. The characteristic velocities of the intrinsic Josephson junctions are estimated to be (1.5–1.8)×106 m/s, which corresponds to the highest velocity mode, from the voltages of Fiske steps and the maximum voltages of the flux-flow branches.

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Highly pure single-crystal Nb films (thickness, ∼2000 Å) with high superconducting transition temperatures Tc of ∼9.3 K and high resistance ratios R300/R10 up to ∼200 are successfully grown epitaxially on single-crystal sapphire (α-Al2O3) and MgO substrates at ∼500–∼700 °C by using an electron-beam evaporation technique. The most high-quality single-crystal Nb film (with the maximum Tc of 9.45 K and the maximum R300/R10 of 199) is obtained on a sapphire (11̄02) substrate, which has a thermal expansion coefficient very close to that of Nb as well as a small lattice misfit to Nb. The quality of obtained single-crystal Nb films is found to be lowered by the deposition of the films on substrates with thermal expansion coefficients different far from that of Nb because of the production of internal strains and lattice defects in the films cooled down.