Effective parameters j/spl tilde//sub c/ and /spl lambda//spl 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 behavior is analogous to that found at zero field and can be understood in terms of a field-dependent effective critical current density j/spl tilde//sub c/ which is smaller than the microscopic value j/sub c/, along with an effective penetration depth /spl lambda//spl tilde//sub J//spl prop//spl radic/(1/j/spl tilde//sub c/) which is larger than /spl lambda//sub J//spl prop//spl radic/(1/j/sub c/). The role of these effective parameters is demonstrated by fitting the peaks in I/sub c/(H) for junctions with both the width and length significantly larger than /spl lambda//spl tilde//sub J/ values, and by a re-scaling of field step structure found in current-voltage curves for commensurate fields which demonstrates their equivalence to the well-known zero field steps found in the absence of applied field.<>