We have measured the angular dependence of the Josephson critical current density (J(C)) in c-axis tilt biepitaxial grain boundary YBa(2)Cu(3)O(7-delta) junctions. We observe for the first time intrinsic d-wave pairing symmetry effects manifested as an oscillatory dependence of J(C) on angle. This intrinsic effect is evident even though spontaneous currents, possibly induced by faceting or barrier impurities, are observed in the grain boundaries.

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We present various concepts and experimental procedures to produce biepitaxial YBa 2 Cu 3 O 7Ϫx grainboundary Josephson junctions. The device properties have an interesting phenomenology, related in part to the possible influence of '' loops.'' The performance of our junctions and superconducting quantum interference devices indicates significant improvement in the biepitaxial technique. Further, we propose methods for fabricating circuits in which 0 and loops are controllably located on the same chip.

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We have recently reported on the persistence of a significant zero voltage current across bicrystal grain boundary junctions of YBa2Cu3O7−δ in an external magnetic field of several Tesla. In this note we present data on the dependence of this residual current on temperature and orientation of the grain boundary. A description of the grain boundary as being comprised of superconducting microbridges separated by normal regions is consistent with the experimental data.

Fabrication of high-temperature superconductor Josephson junctions by focused ion beam milling

The properties of symmetric 24 • and asymmetric 45 • [100] tilt YBa 2 Cu 3 O 7−x bicrystal grain boundary junctions (GBJs) have been extensively investigated. A large number of junctions, with dimensions ranging from 2 to 20 µm, have been fabricated and characterized at 4.2 K. Experimental data have been compared with [001] tilt bicrystal and [100] tilt biepitaxial YBa 2 Cu 3 O 7−x junctions. [100] GBJs show high I c R n products in the range 5-10 mV at T = 4.2 K, these being slightly sensitive to the critical current density values. A direct tunnelling mechanism for both Cooper pair and quasiparticles has been evidenced. The reduced I c R n values of asymmetric 45 • with respect to symmetric 24 • [100] tilt GBJs have been accounted for by considering a d-wave symmetry of the order parameter using the Sigrist-Rice equation.

We report on the magnetic field and angular dependence of the critical current density of epitaxial FeTe0.5Se0.5 thin films. The films exhibit high critical current values and weak dependence on the applied magnetic field. The Jc is larger for field parallel to the c-axis, which is the opposite behavior of what expected from the critical field anisotropy. The analysis of the activation energy for vortex motion indicates that the single pinning regime holds up to 9 T, suggesting that correlated pinning centers are more effective than the vortex-vortex interaction even at the largest applied fields. Scanning tunneling microscope analysis indicates threading dislocations as possible pinning centers.