Abstract
Our previous point-contact Andreev reflection studies of the heavy-fermion superconductor CeCoIn 5 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, CeCoIn 5, CeRhIn 5, and YbAl 3, each with different electron mass. In contrast with Au/CeCoIn 5 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.
Highlights
According to the Blonder–Tinkham–Klapwijk theory [1], Andreev reflection (AR) [2] process is prohibited if the two electrodes have highly disparate Fermi velocities, as in normal-metal/heavy-fermion superconductor junctions
In order to address this question, we have carried out conductance measurements on junctions with three heavyfermion metals (HFN), each with different m* value: ÃCorresponding author
Note the conductance asymmetry in the CeCoIn5/Nb junctions, similar to that observed in Au/CeCoIn5 junctions [5]
Summary
According to the Blonder–Tinkham–Klapwijk theory [1], Andreev reflection (AR) [2] process is prohibited if the two electrodes have highly disparate Fermi velocities, as in normal-metal/heavy-fermion superconductor junctions. In order to address this question, we have carried out conductance measurements on junctions with three heavyfermion metals (HFN), each with different m* value: ÃCorresponding author. Tel.: +1 217 265 5010; fax: +1 217 244 8544. CeCoIn5 (Tc 1⁄4 2.3 K, m*83m0) [7], CeRhIn5 (5–9m0, below TN 1⁄4 3.8 K) [8], and YbAl3 (15–30m0) [9].
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