Electric field versus current density curves in melt-textured samples of YBa_2Cu_3O_(7-δ) under currents well above the critical current

摘要

In this work, we present measurements of the E-J curves of top seeded melt-textured YBa_2Cu_3O_(7-δ).The samples, with a typical 0.5 mm~2 cross section, were cut from monoliths grown up to 2 cm in diameter (ab-planes direction) and 0.7 cm in height (c-axis direction). The E-J characteristics were measured up to current densities several times larger than the critical current density J_C. To avoid spurious heating, current pulses up to 200 A and 1-3 ms long were applied through the samples immersed in liquid nitrogen. Measurements were carried out in the temperature range 80-93 K by pressuring the nitrogen bath. An abrupt electric-field jump is observed, in the E-J curves, for a current density J~* several times higher than J_C-This jump at J~* is to some extent similar to the one observed in thin films.