Coupling to spin excitations revealed in optical data

In a recent paper we showed that there exists a signature of the famous 41 meV neutron spin resonance in the optical data of optimally doped YBa2Cu3O6 .93 (YBCO) and that an absolute estimate of its coupling to the charge carr iers can be made. Here we extend our analysis to Tl2Sr2CuO6+delta (Tl2201) with a T-c = 90 K. The spin resonance is found to be much broader than in Y BCO and then in Bi2Sr2CaCu2O8+delta (Bi2212), although no neutron data exis t as yet. A detailed analysis is given of the superconductivity of Tl2201 i n which the interactions responsible for superconductivity are constructed solely from consideration of optical data.