Resonance mode in $B_{1g}$ Raman scattering -- a way to distinguish   between spin-fluctuation and phonon-mediated $d-$wave superconductivity
  We argue that Raman scattering in $B_{1g}$ symmetry allows one to distinguish between phonon-mediated and magnetically-mediated $d-$wave superconductivity. In spin mediated superconductors, $B_{1g}$ Raman intensity develops a resonance at a frequency $\omega_{res} < 2\Delta_{max}$, whose origin is similar to a neutron resonance. In phonon-mediated $d-$wave superconductors, such a resonance does not develop. Several extensions of the argument are presented. 
A. V. Chubukov, T. P. Devereaux and M. V. Klein