Andreev reflection spectroscopy of the heavy-fermion superconductor CeCoIn${}_5$ along three different crystallographic orientations

Abstract

Andreev reflection spectroscopy has been performed on the heavy-fermion superconductor (HFS) CeCoIn${}_5$ single crystals along three different crystallographic orientations, (001), (110), and (100), using Au tips as counter-electrodes. Dynamic conductance spectra are reproducible over wide temperature ranges and consistent with each other, ensuring the spectroscopic nature. Features common to all directions are: i) asymmetric behaviors of the background conductance, which we attribute to the emerging coherent heavy-fermion liquid; ii) energy scales (~1 meV) for conductance enhancement due to Andreev reflection; iii) magnitudes of enhanced zero-bias conductance (10 - 13 %). These values are an order of magnitude smaller than the predicted value by the Blonder-Tinkham-Klapwijk (BTK) theory, but comparable to those for other HFSs. Using the d-wave BTK model, we obtain an energy gap of ~ 460 ueV. However, it is found that extended BTK models considering the mismatch in Fermi surface parameters do not account for our data completely, which we attribute to the shift of spectral weight to low energy as well as to the suppressed Andreev reflection. A qualitative comparison of the conductance spectra with calculated curves shows a consistency with d${}_{x^2-y^2}$-symmetry, providing the first spectroscopic evidence for the order parameter symmetry and resolving the controversy over the location of the line nodes.

invited talk submitted to the 8th M2S conference to be held in Dresden Germany, July 9-14, 2006, 4 pages, 3 figures

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Cited by in corpus (8)

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• Magneto-transport properties governed by the antiferromagnetic fluctuations in heavy fermion superconductor CeIrIn${}_5$
• Superconducting order parameter in nonmagnetic borocarbides RNi${}_2$B${}_2$C (R=Y, Lu) probed by point-contact Andreev reflection spectroscopy
• Growth, Characterization and Fermi Surface of Heavy Fermion CeCoIn5 Superconductor
• Spectroscopic Evidence for the Direct Involvement of Local Moments in the Pairing Process of the Heavy-Fermion Superconductor CeCoIn${}_5$
• Point-contact Andreev reflection spectroscopy of heavy-fermion-metal/superconductor junctions
• Novel attractive pairing interaction in strongly correlated superconductors