Unusual pressure evolution of the Meissner and Josephson effects in the heavy-fermion superconductor UPt3

The Josephson effect between a single-crystal UPt3 and a conventional superconductor Al has been investigated under pressure for the junction on the UPt3 surface perpendicular to the hexagonal c[0001] axis. Simultaneously measured magnetization has revealed that the Meissner fraction approaches a minimum value of ∼1% at the critical pressure of Pc∼0.4GPa. The critical temperature Tc and the temperature TJ where a measurable Josephson critical current Ic first appears decrease with increasing pressure; the decreasing rate of |dTc/dP| is almost constant, whereas |dTJ/dP| shows an abrupt increase above Pc, indicating that the Josephson effect is suppressed above Pc. These results, together with the decrease in penetration depth λ derived from the magnetic-field dependence of Ic, suggest that the superconducting phase is modified above Pc by the disappearance of the symmetry-breaking antiferromagnetic order.