TRANSITION FROM MAGNETIC FRAUNHOFER-LIKE TO INTERFEROMETRIC BEHAVIOR IN YBCO BRIDGES WITH DECREASING WIDTH

We have performed a detailed study of the magnetic field dependence of the critical current, I-c(B) (B = 0-35 G), for variable width (w) bri dges (w = 50-1000 mu m) mechanically cut in YBCO (101 Ag) thick films on YSZ substrates. The films had J(c) values of similar to 400, 20 and 1 A/cm(2). An interesting experimental regularity is observed. A decr easing width produces in I-c(B) a progressive loss of its average sin( x)/x (Fraunhofer-like) behavior, which is replaced by interferential b ehavior with a large value of residual I-c(B) at the maximum applied B . In the lower J(c) case (1 A/cm(2)) only interferential behavior is o bserved. Regarding our bridges as an aleatory linear array of Josephso n junctions (JJs) in parallel, we have obtained families of curves I-c (B, w), which reproduce in a qualitative manner the observed experimen tal results. The choice of the loop areas formed between JJs is discus sed in detail.