Thermally-activated flux flow (TAFF) resistivity above the irreversibility field is reported for two different c-axis textured MgB_2 superconducting films. Transport measurements at different perpendicular magnetic fields 0 < B < 9 T and temperatures from 5 to 40K reveal TAFF Ohmic resistivity described by the Arrhenius law with the quadratic field dependence of the activation energy. Our transport measurements on bulk MgB_2 ceramic samples also show the TAFF behavior, but do not show the quadratic field dependence of U(T,B). We explain our results in terms of thermally-activated drift of pre-existing quenched dislocations in the vortex lattice. Our results indicate that thermal fluctuations can be essential in determining the irreversibility field in MgB2 though to a much lesser extent than in high-temperature superconductors.
@article{arxiv.cond-mat/0406294,
title = {Thermally-activated current transport in MgB_2 films},
author = {S. Patnaik and A. Gurevich and S. D. Bu and J. Choi and C. B. Eom and D. C. Larbalestier},
journal= {arXiv preprint arXiv:cond-mat/0406294},
year = {2009}
}
Comments
32 Pages, 8 figures, to be published in Physical Review B