Coupling to spin fluctuations from conductivity scattering rates
  A recent analysis of optical conductivity data which has provided strong evidence for coupling of the charge carriers to the 41 meV spin resonance, seen in the superconducting state of optimally doped Y123, is extended to other systems. We find that the corresponding spin resonance is considerably broader in Tl2201 and Y124 than it is in Bi2212. On the other hand, in overdoped Tl2201 with T_c = 23 K no resonance forms. A more specific interpretation of the optical data in terms of a spin fluctuation exchange mechanism of superconductivity gives an underlying effective spectral density which is strongly temperature dependent and which contains important feedback effects that further stabilize superconductivity as the temperature is reduced. 
E. Schachinger and J.P. Carbotte