Point-contact Andreev reflection spectroscopy of heavy-fermion-metal/superconductor junctions

Our previous point-contact Andreev reflection studies of the heavy-fermion superconductor CeCoIn5 using Au tips have shown two clear features: reduced Andreev signal and asymmetric background conductance. To explore their physical origins, we have extended our measurements to point-contact junctions between single crystalline heavy-fermion metals and superconducting Nb tips. Differential conductance spectra are taken on junctions with three heavy-fermion metals, CeCoIn5, CeRhIn5, and YbAl3, each with different electron mass. in contrast with Au/CeCoIn5 junctions, Andreev signal is not reduced and no dependence on effective mass is observed. A possible explanation based on a two-fluid picture for heavy fermions is proposed. Published by Elsevier B.V.