Weak Link Properties of YBa₂Cu₃O_7−δ Thin Film Grain Boundaries

Abstract

Laser ablated YBa₂Cu₃O_7−δ thin films on MgO can have a morphology consisting of large grains with the c axis perpendicular to the film and with the a and b axes in the plane of the substrate along several different principle MgO axes. The resulting films have characteristic high angle grain boundaries which can be isolated by making small lithographic structures. The high angle grain boundaries are found to show weak link behavior including RSJ like IV curves, high sensitivity to magnetic fields, and constant voltage steps when exposed to microwave radiation. Critical current measurements as a function of magnetic field show that there are large variations in the critical current density along the grain boundary. A considerable amount of flux trapping is seen in the grain boundary weak links which may be an intrinsic feature of a disordered high T_c grain boundary.