USE OF TRICRYSTAL JUNCTIONS TO PROBE THE PAIRING STATE SYMMETRY OF YBA2CU3O7

We have developed a new method of probing superconducting pairing stat e symmetry, by using tricrystal devices analogous to s-d corner juncti ons. Two central peaks are observed in the field-modulated critical cu rrents of frustrated YBCO tricrystal junctions operating in the. short junction limit, consistent with predominantly d(x2-y2) - wave pairing symmetry with little or no imaginary s-wave component. However, our r esults are consistent with a real combination of large d-wave and smal l s-wave components. A single peak is also observed for frustrated tri crystal junctions operating in the long junction limit, and it is show n theoretically that the behaviors of s- and d-wave superconductors ar e indistinguishable in this limit.