Evidence against thermal activation as the cause of flux creep in type II superconductors

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Abstract
Voltage-current measurements have been made on lead-indium alloys in transverse magnetic fields with a voltage sensitivity of 10-12 v. By working in fields just below He2 it has been possible to observe the truly exponential dependence of voltage on current which is characteristic of flux creep. The expected temperature dependence of the creep rate, however, appears to be completely absent and it is therefore deduced that the creep does not result from thermal activation. Re-examination of earlier work does not show any clear contradiction of this view, and suggests furthermore that thermally activated creep is a most improbable process.