Singularities in the optical response of cuprates

We argue that the detailed analysis of the optical response in cuprate superconductors allows one to verify the magnetic scenario of superconductivity in cuprates. As for strong coupling charge carriers to antiferromagnetic spin fluctuations, the second derivative of optical conductivity should contain detectable singularities at 2D1Dspin , 4D , and 2D12Dspin , where D is the amplitude of the superconducting gap, and Ds is the resonance energy of spin fluctuations measured in neutron scattering. We argue that there is a good chance that these singularities have already been detected in the experiments on optimally doped Y-Ba-Cu-O.