Andreev reflections on heavy-fermion superconductors

Abstract

In a comparative Andreev-reflection study of normal-superconductor point contacts on the c plane of ${\mathrm{UPt}}_{3}$, ${\mathrm{CeCu}}_{2}$${\mathrm{Si}}_{2}$, and ${\mathrm{URu}}_{2}$${\mathrm{Si}}_{2}$ 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 behavior of the differential resistance dV/dI(V) of ${\mathrm{UPt}}_{3}$ is attributed to the presence of nodes in the superconducting order parameter \ensuremath{\Delta}(k^) and is compared with theoretical predictions for the symmetry of the pairing state. The data for ${\mathrm{CeCu}}_{2}$${\mathrm{Si}}_{2}$ and ${\mathrm{URu}}_{2}$${\mathrm{Si}}_{2}$ point to the absence of zeros in \ensuremath{\Delta}(k^).