| We report evidence for a complex low-temperature superconducting phase in UPt3 that breaks time-reversal symmetry and exhibits a phase shift of pi in the superconducting order parameter between the a- and b-axes. We also report evidence for nodes in the amplitude of the superconducting energy gap in the high-temperature phase of UPt3. These nodes occur 45° between the a - and b-axes and fill in as an out-of-phase energy gap component develops. This evidence supports the E 2u representation of the superconducting order parameter. These measurements were taken by fabricating Pb-Cu-UPt 3 Josephson junctions on polished and as-grown surfaces of UPt3 single crystals. By measuring the critical current through the junctions and varying the applied magnetic field, temperature, and angle of the junctions, we obtained information on the phase and magnitude of the superconducting order parameter. |
