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

TL;DR

This study investigates point-contact Andreev reflection spectroscopy on heavy-fermion metal/superconductor junctions, revealing differences from previous Au tip measurements and proposing a two-fluid model to explain the observations.

Contribution

It extends previous work by using single crystalline heavy-fermion metals with Nb tips, showing no reduction in Andreev signal and suggesting a two-fluid explanation.

Findings

Andreev signal not reduced in heavy-fermion junctions with Nb tips

No dependence of conductance on effective mass observed

Proposed two-fluid model for heavy fermions

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 [1]. 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. [1] W. K. Park et al., Phys. Rev. B 72 052509 (2005); W. K. Park et al., Proc. SPIE-Int. Soc. Opt. Eng. 5932 59321Q (2005); W. K. Park et al., Physica C (in press) (cond-mat/0606535).