Inversion of optical conductivity in Bi2Sr2CaCu2O8+δ

We have extracted the spectral function, using an inversion scheme, for optimal and underdoped Bi₂Sr₂CaCu₂O_8+δ in both normal and superconducting states. The derived spectral functions reproduce features of resonance peaks in the superconducting state and the magnetic excitation spectrum in the normal state, as observed previously in inelastic neutron scattering experiments. We also illustrate how these features show up in the raw optical spectra. The results provide further support for the scenario that the charge carriers interact through antiferromagnetic spin fluctuations.