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 paper, 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 La2-xSrxCuO4 (LSCO), YBa2Cu3O6+x (YBCO), and Bi2Sr2CaCu2O8+x (Bi2212) in their superconducting and nonsuperconducting phases. In particular, the question of the universality of the magnetic excitation spectrum will be addressed.