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A study of the superconducting gap in RNi$_2$B$_2$C (R = Y, Lu) single crystals by inelastic light scattering

In-Sang Yang·M. V. Klein·S. L. Cooper·P. C. Canfield·B. K. Cho·Sung-Ik Lee
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Abstract

Superconductivity-induced changes in the electronic Raman scattering response were observed for the RNi$_2$B$_2$C (R = Y, Lu) system in different scattering geometries. In the superconducting state, 2$Δ$-like peaks were observed in A$_{1g}$, B$_{1g}$, and B$_{2g}$ spectra from single crystals. The peaks in A$_{1g}$ and B$_{2g}$ symmetries are significantly sharper and stronger than the peak in B$_{1g}$ symmetry. The temperature dependence of the frequencies of the 2$Δ$-like peaks shows typical BCS-type behavior, but the apparent values of the $2Δ$ gap are strongly anisotropic for both systems. In addition, for both YNi$_2$B$_2$C and LuNi$_2$B$_2$C systems, there exists reproducible scattering strength below the $2Δ$ gap which is roughly linear to the frequency in B$_{1g}$ and B$_{2g}$ symmetries. This discovery of scattering below the gap in non-magnetic borocarbide superconductors, which are thought to be conventional BCS-type superconductors, is a challenge for current understanding of superconductivity in this system.

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In-Sang Yang, M. V. Klein, S. L. Cooper, P. C. Canfield, B. K. Cho, Sung-Ik Lee. 2000-04-17. A study of the superconducting gap in RNi$_2$B$_2$C (R = Y, Lu) single crystals by inelastic light scattering. https://doi.org/10.1103/physrevb.62.1291

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