Magnetic field dependence of YBCO Josephson junction array

We have fabricated YBCO step-edge Josephson junctions and Josephson junction arrays. The steps are formed by Ar ion-milling on various substrates. The I-V characteristics show a RSJ-like behavior at temperature even above 77 K. Using the optimized single junction fabrication procedure, two dimensional square junction arrays of various sizes are made. I-c and R(n) value scale reasonably well with array size, indicating uniform junction formation. Their I-V and dV/dI characteristics are measured and the I-c distribution is estimated. We also measured the magnetoresistance as a function of bias current and temperature, which shows periodic structure with the period of Phi(0) per unit cell, with a parabolic background. Frustration effects, e.g., resistivity minima at fractional magnetic flux quantum per unit cell, are clearly observable.