Dynamic Response Functions from Angle Resolved Photoemission Spectra

We introduce a formalism for calculating dynamic response functions using experimental single-particle Green's functions. As an illustration of this procedure, we estimate the dynamic spin-response of the cuprate superconductor Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}}. We find good agreement with superconducting state neutron data, in particular, the ({pi},{pi}) resonance with its unusual 'hourglass' shaped dispersion. We anticipate that our formalism will also be useful in interpreting results from other spectroscopies, such as optical and Raman responses.