Study of the superconducting gap in RNi2B2C (R = Y, Lu) single crystals by inelastic light scattering

Abstract

Superconductivity-induced changes in thr electronic Raman-scattering response were observed for the RNi2B2C (R =Y, Lu) system in different scattering geometries. In the superconducting state, 2 Delta-like peaks were observed in A(1g), B-1g, and B-2g spectra from single crystals. The peaks, in A,, and Bz, symmetries are significantly sharper and stronger than the peak in B-1g symmetry. The temperature dependence of the frequencies of the 2 Delta-like peaks shows typical BCS-type behavior, but the apparent values of the 2 Delta gap are strongly anisotropic for both systems. In addition, for both YNi2B2C and LuNi2B2C systems, there exists reproducible scattering strength below the 2 Delta gap which is roughly linear to the frequency in B-1g and B-2g symmetries. This discovery of scattering below the gap in nonmagnetic borocarbide superconductors, which are thought to be conventional BCS-type superconductors. is a challenge for current understanding of superconductivity in this system.