VORTEX CORRELATIONS IN THE SUPERCONDUCTING TRANSITION OF YBA2(CU1-XALX)3O7-DELTA FILMS IN HIGH MAGNETIC-FIELDS

We determine the characteristic length scale for vortex correlations i n YBa2(Cu1-xAlx)3O7-delta films [0 less-than-or-equal-to x less-than-o r-equal-to 0.03] by studying their current-voltage characteristics in fields 0.5 T less-than-or-equal-to B less-than-or-equal-to 6 T. We fin d that critical scaling persists over 60% of the resistive transition (which widens from 3 to 30 K as doping concentration and field increas e) and breaks down when the correlation length is 500-1250 angstrom, a value that does not depend on the intervortex spacing. This result su ggests that pinning in as-made films of YBa2Cu3O7-delta is dominated b y extended rather than microscopic defects.