Electric field versus current density curves in melt-textured samples of YBa 2Cu 3O 7− δ under currents well above the critical current

Abstract

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.