Signature of spin fluctuation structure in optical conductivity

Although optical techniques can, in principle, be used in conventional supe rconductors to obtain the electron-phonon spectral density, the method of c hoice has been tunneling. Because the oxides are poor metals in comparison to conventional systems, good reflectance data has been routinely obtained and analyzed to extract the frequency dependence of the optical scattering rate, 1/tau(omega). This quantity contains information on the spin fluctuat ion spectrum, should this be a dominant, inelastic, scattering mechanism. U sing the nearly antiferromagnetic Fermi liquid as a model, it is shown how structure in the spin susceptibility, chi, is reflected in an appropriately chosen second derivative of 1/tau. (C) 1998 Elsevier Science Ltd. All righ ts reserved.