YBa₂Cu₃O_7-x Josephson junctions and dc SQUIDs based on 45° a -axis tilt and twist grain boundaries: atomically clean interfaces for applications

YBa₂Cu₃O_7-x artificial grain boundary Josephson junctions have been fabricated, employing a recently implemented biepitaxial technique. The grain boundaries can be obtained by controlling the orientation of the MgO seed layer and are characterized by a misalignment of the c-axes (45° a-axis tilt or 45° a-axis twist). These types of grain boundaries are still mostly unexplored. We carried out a complete characterization of their transport properties and microstructure. Junctions and dc SQUIDs associated with these grain boundaries exhibit an excellent Josephson phenomenology and high values of the I_CR_N product and of the magnetic flux-to-voltage transfer parameter respectively. Remarkable differences in the transport parameters of tilt and twist junctions have been observed, which can be of interest for several applications. A maximum speed of Josephson vortices as calculated from the voltage step values of the order of 2 × 10⁶ m s^-1 is obtained.These devices could also have some impact on experiments designed to study the symmetry of the order parameter, exploiting their microstructure and anisotropic properties. High-resolution electron microscopy showed the presence of perfect basal plane faced boundaries in the cross sections of tilt boundaries.