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Transport in ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ was studied by modulating the resistance and superconductive kinetic inductance via capacitively charging (001) surfaces. The mobility varies inversely with temperature, the effective mass is 5(\ifmmode\pm\else\textpm\fi{}1)${\mathit{m}}_{\mathit{e}}$ at low tmeperature, and hole carrier densities are temperature independent and nearly the same in normal and superconducting states. Transition temperatures at ideal surfaces are equal to the bulk and show notably weak modulation with carrier density.

The authors give a revised effective mass of the cooper pairs and its temperature dependence for the YBCO high{minus}Tc superconductors. (AIP)

Milling with Xenon ions directed at grazing angles onto the surfaces of c-axis oriented YBa2Cu3O7 films is shown to give smooth films which superconduct at thicknesses approaching a lattice constant. The observed linear dependence of the room temperature sheet conductance with milling time allows a determination of the effective electrical thickness after each milling stage. The resistance transitions of all films having a superconducting transition show a metallic behavior with a positive temperature coefficient of resistance. Degradation of superconducting properties becomes significant for films less than 100A thick although this degradation is appreciably less for films which initially (before milling) have sharp resistance transitions and a strong c-axis orientation. Reproducible and controlled fabrication of ultrathin films using this milling technique shows promise as an important step in the post-deposition processing of high- Tc thin films for electronic device applications.

Discrete conductance increments in the current-voltage characteristics of superconductor-insulator-superconductor tunnel junctions (of area ⪕25 μ m 2 ) associated with single flux quanta (“vortices”) trapped in the thin film electrodes have been observed. These tunneling results were obtained for both Sn and Pb and provide, for the first time, a direct measure of the density of quasiparticle states corresponding to a single vortex. Simultaneous measurements of the Josephson critical current suppresion indicate that the vortex cores are on the average not aligned across the barrier on the scale of the coherence lenght. The measured vortex density of states is in disagreement with predictions of the normal cores model and previously published data.

Sputtering of a magnesium target with a beam of argon ions in the presence of a partial pressure of reactive oxygen gas has been found to yield smooth MgOx thin‐film dielectrics with low electrical loss, good mechanical stability, and excellent reproducibility. The films consist of polycrystalline MgO with a grain size ≲50 A and an OH‐containing component. The thickness dependence of the areal capacitance is discussed in the context of a two‐layer model in which this oxygen‐rich phase (x≂1.4) overlays a thin (≲40 A) stoichiometric phase (x≂1.0). Observation of superconducting tunneling characteristics in trilayer Au‐MgOx‐Pb structures confirms pinhole‐free coverage which may have possible application as artificial tunnel barriers.

An electrodynamic balance has been constructed in which the perturbative forces from applied magnetic fields are used to probe the superconducting properties of single levitated charged grains of high Tc superconductors with diameters ≲10 μm. The low‐temperature magnetization of selected Ba2YCu3O7 grains has been observed to exhibit a flux exclusion near 80% of the theoretical maximum. Hysteresis, flux creep, and the lower critical field are identified.

We describe a method for measuring the position of a Josephson junction from outside the cryostat. An inhomogeneous ac magnetic field from two opposed coils modulates the critical current of the junction unless it is in the central region where the field is small. We use the technique to measure the critical current of individual junctions in a series‐connected array, using electrical contacts across the entire string.