Critical Current of Superconducting ${rm YBa}_{2}{rm Cu}_{3}{rm O}_{7-delta}$ Films With Different In-Plane Orientations

摘要

By using a pulsed-laser deposition (PLD) technique, we grow high quality ${rm YBa}_{2}{rm Cu}_{3}{rm O}_{7-delta}$ films on YSZ (Yt-stabilized Zr) substrates with 0-degree and 45-degree in-plane orientations at 810 $^{circ}{rm C}$ and 690 $^{circ}{rm C}$ respectively. Surprisingly, despite the large difference in growth temperature the qualities of the films are almost the same. To study the subtle differences between these two types of films, we measured both the temperature and magnetic field dependencies of the critical current. Although there is very little difference in their magnetic field dependence, there is a distinct temperature dependence, i. e. $J_{c}(1-{rm T}/{rm T}_{rm c})$ proportional to $(1-{rm T}/{rm T}_{rm c})^{5/4}$ for 0 degree in-plane orientation and proportional to $(1-{rm T}/{rm T}_{rm c})^{3/2}$ for 45 degree in-plane orientation at temperatures near ${rm T}_{rm c}$. We also studied the critical current densities with different fractions of mixed orientations, and found an empirical formula $J_{c}propto e^{5alpha}$ where $alpha$ is the fraction of the majority domain.