Critical flux pinning and enhanced upper critical field in magnesium diboride films
نویسندگان
چکیده
We have conducted pulsed transport measurements on c-axis-oriented magnesium diboride films over the entire relevant ranges of magnetic field 0&H&Hc2 ~where Hc2 is the upper critical field! and current density 0& j& jd ~where jd;10 7 A/cm is the depairing current density!. The intrinsic disorder of the films combined with the large coherence length and three dimensionality, compared to cuprate superconductors, results in a sixfold enhancement of Hc2 ~to 1763 T) and raises the depinning current density j c to within an order of magnitude of jd . The current-voltage response has an unusually steep nonlinear shape at all fields, resulting from a combination of depinning and pair breaking, and has no trace of an Ohmic free-flux-flow regime.
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