EXPLANATION OF THE DISSIPATION OBSERVED IN SEVERAL HIGH-TEMPERATURE SUPERCONDUCTORS USING A MODIFIED AMBEGAOKAR-HALPERIN MODEL

We have measured the current-voltage (I-V) characteristics of several high-temperature-superconducting materials with widely different morph ologies (bulk Ag/Pb-Bi-Sr-Ca-Cu-O tapes, thin films of Y-Ba-Cu-O, and melt-textured, bulk Y-Ba-Cu-O samples). The I-V curves were taken at s everal magnetic fields ranging from 0 to 8 T. The measurements were ca rried out at three temperatures (4.2, 27, and 77 K) where the samples were immersed in liquid cryogens to ensure good thermal equilibrium. W e compared our experimental results to the predictions of dissipation in superconductors made by the following physical models: modified Amb egaokar-Halperin, flux creep, vortex glass, collective flux creep, and a power law. The fits were extremely good for the first model and wer e not nearly as good for the others. Using the modified Ambegaokar-Hal perin model, the critical current I(c), the normal-state resistance R( n), and gamma, which is proportional to the pinning potential U (H,T), were obtained for each material. Since the Ambegaokar-Halperin model is the only one which uniquely defines I(c), we conclude that its use puts this parameter on a solid physical basis.