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arXiv · 1004.3846

Superconducting order parameter in nonmagnetic borocarbides RNi$_{2}$B$_{2}$C (R=Y, Lu) probed by point-contact Andreev reflection spectroscopy

X. Lu·W. K. Park·S. Yeo·K. -H. Oh·S. -I. Lee·S. L. Bud'ko·P. C. Canfield·L. H. Greene
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Abstract

We report on the measurements of the superconducting order parameter in the nonmagnetic borocarbides LuNi$_2$B$_2$C and YNi$_2$B$_2$C. Andreev conductance spectra are obtained from nanoscale metallic junctions on single crystal surfaces prepared along three major crystallographic orientations: [001], [110], and [100]. The gap values extracted by the single-gap Blonder-Tinkham-Klapwijk model follow the BCS predictions as a function of temperature and magnetic field and exhibit a small anisotropy. These observations are robust and reproducible among all the measurements on two different sets of LuNi$_2$B$_2$C crystals and one set of YNi$_2$B$_2$C crystals. We suggest possible explanations for the small gap anisotropy based on the recent detailed gap measurements by angle-resolved photoemission spectroscopy and the tunneling cone effect. Our results provide a consistent picture of the superconducting gap structure in these materials, addressing the controversy particularly in the reported results of point-contact Andreev reflection spectroscopy.

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X. Lu, W. K. Park, S. Yeo, K. -H. Oh, S. -I. Lee, S. L. Bud'ko, P. C. Canfield, L. H. Greene. 2010-04-22. Superconducting order parameter in nonmagnetic borocarbides RNi$_{2}$B$_{2}$C (R=Y, Lu) probed by point-contact Andreev reflection spectroscopy. https://doi.org/10.1103/physrevb.83.104519

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