Angular dependence of the symmetry of the order parameter in YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//

Using a 4.2 K scanning SQUID microscope, we examined twinned thin-film YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO)-Ag-PbIn SQUIDs and measured the phase of the order parameter in the YBCO for 13 different tunneling angles. We have found that the order parameter in YBCO is time-reversal symmetric and shows a d(x/sup 2/-y/sup 2/)-pairing symmetry, provided the junctions are properly made. Detailed analysis of our data reveals that any time-reversal breaking component is less than 5%, which rules out states such as d(x/sup 2/-y/sup 2/)+ is or d(x/sup 2/-y/sup 2/)+ id/sub xy/.