Measurement of the Josephson effect of heavy-fermion superconductor UPt3 as a test of the odd-parity order parameter

The Josephson critical current Ic between a single-crystal UPt3 and Al has been measured for the junctions on the UPt3 surface perpendicular to the hexagonal a[112-bar0], b[101-bar0], and c[0001] axes. The magnetic field dependence of Ic shows a Fraunhofer diffraction pattern for a current flow parallel to the c-axis, suggesting that the Josephson coupling is uniform throughout the junction. Small modifications applied to the Fraunhofer pattern have been observed for a current flow parallel to the a- and b-axes. These results contradict the E2u scenario for the odd-parity order parameter in UPt3, in which the Josephson effect is forbidden in the three directions, whereas the recently proposed E1u scenario permits, at least, the a- and c-axis Josephson couplings. (author)