Controlling the natural strong pinning sites in laser ablated YBa2Cu3O7-delta thin films

Recently [1], we have shown that dislocations are the most important flux p inning centers in Pulsed Laser Deposited YBa2Cu3O7-delta thin films. It app eared that the magnetic field upto which the critical current remains const ant, is roughly equal to the matching field B-Phi=n(disl)Phi (0), with n(di sl) the density of dislocations. Here, we investigate the formation mechani m of these dislocations. Using wet-chemical etching in combination with Ato mic Force Microscopy, we find that dislocations are induced in the first st ages of film growth and persist all the way up to the film surface parallel to the c-axis. Since the substrate temperature can be used to tune the def ect density n(disl), the dislocation formation mechanism is closely related to the YBa2Cu3O7-delta nucleation and growth mechanism. We propose that di slocations are induced as a result of merging of misaligned growth fronts d ue to the preferential formation of precipitates in the first stages of gro wth. Indeed, we find that we can increase the dislocation density by first depositing Y2O3 precipitates.