THE EXPONENTIAL CRITICAL-STATE OF HIGH-TC CERAMICS

The critical current in high-Tc materials is strongly reduced by a mag netic field. We studied this dependency for tubular YBCO samples. We f ind an exponential drop as the field is increased from zero up to some tens of oersted. This behavior was already observed by others, howeve r little work has been done in this direction. We define what we call the 'exponential critical state' of HTSC and compare the prediction fo r the magnetization with experimental data. Furthermore, the 'Kim crit ical state' is obtained as the small field limit.