Transport characteristics of Tl2Ba2CaCu2O8 bicrystal grain boundary junctions at 77 K

Abstract

We report the fabrication and characterization of thin-film grain boundary junctions in Tl-based superconductors on bicrystal substrates. Post-deposition processed Tl2Ba2CaCu2O8 films were grown on bicrystal SrTiO3 substrates, with varying degrees of misorientation angle θ. Critical current densities and current-voltage curves had a strong dependence on θ. For θ≥10°, there was a two-to-three order of magnitude reduction in critical current density, and for θ≥20°, the current-voltage curves displayed resistively shunted junction behavior. These high angle grain boundary junctions have features at 77 K that are attractive for device applications, including sharp voltage onsets, well-behaved dc magnetic and rf field dependence, IcRn products as large as 300 μV, and low 1/f noise. Simple dc superconducting quantum interference devices fabricated with these junctions exhibited transfer functions of up to 30 μV/Φ0 at 77 K.

The Nature of Grain Boundaries in the High-Tc Superconductors

“…Evidence that the transition to weak-link behavior can be pushed to e � 20° in bulk-scale YBCO bicrys tals processed by partial melting (6) suggests that it might be possible to reduce the effective size of the dislocation core to the conventional value, if the dislocation model, indeed, pertains. Possibly similar behavior was observed for TBCCO-2212 epitaxial bicrystals, although the fi lm quality caused a question as to whether the lc decrease was continuous or saturated to a plateau (34). However, the characteristics of other types of bicrys tals have revealed an important variation indicative of a more complex origin for the weak-link behavior than dislocation PGBD overlap.…”

A Search for a Low Anisotropic Superconductor

“…The highest critical current density in double layer TlO compounds is attained in Tl-2223 thin films, which is of the order of 107 A/cm 2 (90K, 0T) [5]. On the other hand the critical current density of Tl-2212 superconductor is in the range of 10 5 -10 6 A/cm 2 at 77K depending upon the deposition techniques used [42][43][44][45][46].…”

Defect alignment in grain boundaries as quantum wells

“…17 The strong flux-pinning action at low-angle g.b.s 18 and the application of g.b. conduction anisotropy in SQUIDS 19 as well as the enhanced spectral response of g.b.s with t Ͼ5°with a peak, normalized response of 50 times that of the film 20 and other work in this line 21,22 has shown that the early measured galvanomagnetic effects in the above-defined g.b.s 4 were representative of the particular features of these structues as quantum wells.…”