Possible origins of resistive tails and critical currents in high-temperature superconductors in a magnetic field

Abstract

The universal lack of a Lorentz-force dependence on dissipation for fields parallel to the CuO2 planes of the highly anisotropic high-temperature superconductor Tl2Ba2CaCu2Ox questions whether flux motion is the cause of this dissipation. We report measurements over a wide range of current densities, in the broadened resistive transitions, current-voltage characteristics I(V), and critical current densities Jc. We rule out the suggestion that this effect is caused by vortices in the CuO2 planes, due to a small misalignment of fields parallel to these planes: That model requires a significantly larger field component perpendicular to the planes than is reasonable, based on the measured alignment of the samples and crystal axes. Instead, we consider a Josephson-coupling model that is consistent with the broadened resistive transitions and the lack of Lorentz-force dependence. A detailed comparison of the predictions of these models is made: The Josephson-coupling model is consistent with the temperature dependences of the activation energy U and Jc, and is better matched to the weak-field dependence of Jc; while the flux-creep model fits the experimental result for U, but it predicts a much stronger temperature and field dependence of Jc than is found. Possible origins of Josephson junctions in high-quality films and single crystals are discussed. For the data with the field parallel to the c axis, a conventional flux-flow explanation is also quite reasonable.

Source-reported materials — not catalogue approval

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