Josephson-like properties of YBa2Cu3O7 thin film weak links

Thin-film YBa₂Cu₃O₇ microbridges have been fabricated by photo- and e-beam lithography in polycrystalline thin films grown on MgO substrates and containing a controlled density of large-angle tilt boundaries, thereby isolating individual tilt-boundary weak links. Depending on the growth parameters of the film, such weak links have critical current densities J_c ranging from <10⁴ A|cm² to >10⁶ A|cm². The higher J_c microbridges exhibit behavior indicative of one-dimensional flux flow and flux creep in the weak links, while the lower J_c microbridges have RSJ-like properties. Detailed comparisons have been made between the predictions of the resistively shunted junction (RSJ) model including the calculated effects of thermal noise rounding and the measured DC and microwave response of these weak links. Measurements have also been made of magnetic field effects on the critical current density. An unexpected scaling behavior has been observed in the I -V characteristics of certain types of these microbridges containing 45° tilt boundaries that indicates that in those cases I_CR_N² is a constant for the tilt-boundary weak link. The implications of these results for developing a successful description of the superconductive properties of YBa₂Cu₃O₇ grain boundary weak links, which electron microscopy reveals to be clean, stoichiometric, and abrupt, are discussed