ANDREEV REFLECTIONS ON HEAVY-FERMION SUPERCONDUCTORS

In a comparative Andreev-reflection study of normal-superconductor poi nt contacts on the c plane of UPt3, CeCu2Si2, and URu2Si2 crystals at temperatures down to T = 30 mK and in a magnetic field up to B = 10 T, differences are found in the current-voltage characteristics. The beh avior of the differential resistance dV/dI(V) of UPt3 is attributed to the presence of nodes in the superconducting order parameter DELTA(k) and is compared with theoretical predictions for the symmetry of the pairing state. The data for CeCu2Si2 and URu2Si2 point to the absence of zeros in DELTA(k).