Linear Response Theory and the Universal Nature of the Magnetic Excitation Spectrum of the Cuprates

Linear response theory, commonly known as the random phase approximation (RPA), predicts a rich magnetic excitation spectrum for d-wave superconductors. Many of the features predicted by such calculations appear to be reflected in inelastic neutron scattering data of the cuprates. In this article, I will present results from RPA calculations whose input is based on angle resolved photoemission data, and discuss possible relevance to inelastic neutron scattering data of LSCO, YBCO, and Bi2212 in their superconducting and non-superconducting phases. In particular, the question of the universality of the magnetic excitation spectrum will be addressed.