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 similar to 1% at the critical pressure of P-c similar to 0.4 GPa. The critical temperature T-c and the temperature T-J where a measurable Josephson critical current I-c first appears decrease with increasing pressure; the decreasing rate of vertical bar dT(c)/dP vertical bar is almost constant, whereas vertical bar dT(J)/dP vertical bar shows an abrupt increase above P-c, indicating that the Josephson effect is suppressed above P-c. These results, together with the decrease in penetration depth lambda derived from the magnetic-field dependence of I-c, suggest that the superconducting phase is modified above P-c by the disappearance of the symmetry-breaking antiferromagnetic order.