Suppressed Andreev Reflection at the Normal-Metal / Heavy-Fermion Superconductor CeCoIn${}_5$ Interface

Abstract

Dynamic conductance spectra are taken from Au/CeCoIn${}_5$ point contacts in the Sharvin limit along the (001) and (110) directions. Our conductance spectra, reproducibly obtained over wide ranges of temperature, constitute the cleanest data sets ever reported for HFSs. A signature for the emerging heavy-fermion liquid is evidenced by the development of the asymmetry in the background in the normal state. Below $T_c$, an enhancement of the sub-gap conductance arising from Andreev reflection is observed, with the magnitude of $\sim$ 13.3 % and $\sim$ 11.8 % for the (001) and the (110) point contacts, respectively, an order of magnitude smaller than those observed in conventional superconductors but consistent with those in other HFSs. Our zero-bias conductance data for the (001) point contacts are best fit with the extended BTK model using the d-wave order parameter. The fit to the full conductance curve of the (001) point contact indicates the strong coupling nature ($2\Delta /k_B{T}_c=4.64$). However, our observed suppression of both the Andreev reflection signal and the energy gap indicates the failure of existing models. We provide possible directions for theoretical formulations of the electronic transport across an N/HFS interface. Several qualitative features observed in the (110) point contacts provide the first clear spectroscopic evidence for the $d_{x^2-y^2}$ symmetry.

13 pages, 7 figures, LaTeX, paper invited and submitted to SPIE Conference on Strongly Correlated Electron Materials: Physics and Nanoengineering, in San Diego, California, July 31 - August 4, 2005

References in corpus (7)

• Andreev - Saint James reflections: a probe of cuprate superconductors
• The role of critical current on point contact Andreev Reflection spectrum between a normal metal and a superconductor
• Spectroscopic Evidence for Multiple Order Parameter Components in the Heavy Fermion Superconductor CeCoIn_5
• Anomalous quasiparticle transport in the superconducting state of CeCoIn5
• Point-Contact Spectroscopy of the Heavy-Fermion Superconductor CeCoIn${}_5$
• Hexagonal and Square Flux Line Lattices in CeCoIn5
• Comment on "Spectroscopic Evidence for Multiple Order Parameters in the Heavy Fermion Superconductor CeCoIn5"

Cited by in corpus (2)

• Comment on "Spectroscopic Evidence for Multiple Order Parameter Components in the Heavy Fermion Superconductor CeCoIn${}_5$"
• Electrical and thermal transport through $\alpha -T_3$ NIS junction