YBa_2Cu_3O_(7-x) Josephson junctions and dc SQUIDs based on 45beg a-axis tilt and twist grain boundaries: atomically clean interfaces for applications

摘要

YBa_2Cu_3O_(7-x) artificial grain boundaryJosephson junctions have been fabricated, employing a recentlyimplemented biepitaxial technique. The grain boundaries can beobtained by controlling the orientation of the MgO seed layer andare characterized by a misalignment of the c-axes (45beg a-axis tiltor 45beg a-axis twist). These types of grain boundaries are stillmostly unexplored. We carried out a complete characterization oftheir transport properties and microstructure. Junctions and dcSQUIDs associated with these grain boundaries exhibit anexcellent Josephson phenomenology and high values of theI_CR_N product and of the magnetic flux-to-voltage transferparameter respectively. Remarkable differences in the transportparameters of tilt and twist junctions have been observed, whichcan be of interest for several applications. A maximum speed ofJosephson vortices as calculated from the voltage step values ofthe order of 2 X 10~6 m s~-1 is obtained. These devices could alsohave some impact on experiments designed to study the symmetryof the order parameter, exploiting their microstructure andanisotropic properties. High-resolution electron microscopyshowed the presence of perfect basal plane faced boundaries in thecross sections of tilt boundaries.