Unconventional electronic Raman spectra of borocarbide superconductors

Borocarbide superconductors, which are thought to be conventional BCS-type superconductors, are not so conventional in several electronic Raman properties. Anisotropic gap-like features and finite scattering strength below the gap were observed for the $R$Ni$_2$B$_2$C ($R$ = Lu, Y) systems in our previous study. The effects of Co-doping on the 2$\Delta$ gap-like features and the finite scattering strength below and above the gap are studied in $R$ = Lu (B = B$^{11}$) system. In superconducting states, Co-doping strongly suppresses the 2$\Delta$ peak in both B$_{2g}$ and B$_{1g}$ symmetries. Raman cross-section calculation which includes inelastic scattering shows a relatively good fit to the features above the 2$\Delta$ peak, while it does not fully account for the features below the peak.