PHASE-SENSITIVE TUNNELING MEASUREMENTS IN A BULK YBA2CU3O7-DELTA DC SQUID

We use Josephson tunneling in a bulk YBa2Cu3O7-delta bicrystal SQUID t o investigate methods of determining the order parameter symmetry from transport measurements. We discuss procedures designed to eliminate t he effects of self-fields due to transport currents in the sample, and apply these methods to our experimental system. The bulk bicrystal SQ UID is designed to give zero phase shift in the event of pure s- or d- wave symmetry, and hence is an ideal experimental test of our analysis procedures. We find a method exploiting the time-reversal invariance of the SQUID equations (independent of the gap time-reversal propertie s) to be most useful.