Evidence for Complex Superconducting Order Parameter Symmetry in the Low-Temperature Phase of Upt3 from Josephson Interferometry

We present data on the modulation of the critical current with applied magnetic field in UPt 3 -Cu-Pb Josephson junctions and SQUIDs. The junctions were fabricated on polished surfaces of UPt 3 single crystals. The shape of the resulting diffraction patterns provides phase-sensitive information on the superconducting order parameter. Our comer junction data show asymmetric patterns with respect to magnetic field, indicating a complex order parameter, and both our junction and SQUID measurements point to a phase shift of π, supporting the E 2u representation of the order parameter.