EFFECTIVE PARAMETERS (J)OVER-TILDE(C) AND (LAMBDA)OVER-TILDE(J) AT COMMENSURATE FIELDS IN LARGE JOSEPHSON-JUNCTIONS WITH PERIODIC COLUMNAR DEFECTS

We have studied flux pinning effects in large Josephson junctions with lithographically patterned periodic columnar defects. At commensurate fields of an integral number of fluxons per defect, the junction beha vior is analogous to that found at zero field and can be understood in terms of a field-dependent effective critical current density <(j)ove r tilde (c)> which is smaller than the microscopic value j(c), along w ith an effective penetration depth <(lambda)over tilde (J)> proportion al to root 1/<(j)over tilde (c)> which is larger than lambda(J) propor tional to root 1/j(c). The role of these effective parameters is demon strated by fitting the peaks in I-c(H) for junctions with both the wid th and length significantly larger than <(lambda)over tilde (J)> value s, and by a re-scaling of field step structure found in current-voltag e curves for commensurate fields which demonstrates their equivalence to the well- known zero field steps found in the absence of applied fi eld.