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 UPt3-Cu-Pb Josephson junctions and SQUIDs. The junctions were fabricated on polished surfaces of UPt3 single crystals. The shape of the resulting diffraction patterns provides phase-sensitive information on the superconducting order parameter. Our corner 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 pi, supporting the E-2u representation of the order parameter.