Characteristics of ybco squids with step-edge and biepitaxial grain boundaries

Some characteristics of YBCO SQUIDs with stepedge and biepitaxial grain boundaries were investigated. V-I curves of the step-edge SQUIDs can be described by the RSJlikc model with a linear relationship between the critical, current Ic and temperature T, whereas the typical IC-T curve for the biepitaxial SQUIDs concaved upward at temperatures near the critical temperature. The V-I curves of both kinds of the stepedge and the biepitaxial SQUIDs under microwave irradiation revealed integral Shapiro steps. Furthermore, the voltages of the step-edge SQUIDs were well modulated by the applied magnetic field. And also, the typical Fraunhofer diffraction of the lc-t> curve was observed for the single junction in the step-edge SQUIDs. On the other hand, the magnetic field modulated voltage oscillation was also found for the biepitaxial SQUIDs. All the details will be discussed in this report.