Electrodynamics of single-crystal Eu/sub 2/CuO/sub 4/: A boson excitation spectrum

Static and microwave measurements of the electronic response of the planar cuprate Eu/sub 2/CuO/sub 4/ provide evidence for thermally activated collective excitations. These observations together with microwave and other measurements on superconductors suggest that paired charge--carrying objects may exist both above and below T/sub c/ in the superconductors. If these objects, which can be related to solitons of a spin density wave ground state, play a role in superconductivity, certain conclusions may be drawn. We discuss here the evidence for such objects and their implications. 19 refs., 5 figs