Unusual pressure evolution of the Meissner and Josephson effects in the heavy-fermion superconductorUPt3

Abstract

The Josephson effect between a single-crystal ${\mathrm{UPt}}_{3}$ and a conventional superconductor Al has been investigated under pressure for the junction on the ${\mathrm{UPt}}_{3}$ surface perpendicular to the hexagonal $c[0001]$ axis. Simultaneously measured magnetization has revealed that the Meissner fraction approaches a minimum value of $\ensuremath{\sim}1%$ at the critical pressure of ${P}_{\mathrm{c}}\ensuremath{\sim}0.4\phantom{\rule{0.28em}{0ex}}\mathrm{GPa}$. The critical temperature ${T}_{\mathrm{c}}$ and the temperature ${T}_{\mathrm{J}}$ where a measurable Josephson critical current ${I}_{\mathrm{c}}$ first appears decrease with increasing pressure; the decreasing rate of $|d{T}_{\mathrm{c}}/dP|$ is almost constant, whereas $|d{T}_{\mathrm{J}}/dP|$ shows an abrupt increase above ${P}_{\mathrm{c}}$, indicating that the Josephson effect is suppressed above ${P}_{\mathrm{c}}$. These results, together with the decrease in penetration depth $\ensuremath{\lambda}$ derived from the magnetic-field dependence of ${I}_{\mathrm{c}}$, suggest that the superconducting phase is modified above ${P}_{\mathrm{c}}$ by the disappearance of the symmetry-breaking antiferromagnetic order.