Phenomenological constraints on theories for high temperature superconductivity

In this paper, the author first presents some of the key experimental results on the normal state properties of the Cu-O superconductors. The author shows that there is a single, rather general, hypothesis about the excitation spectrum from which the perplexing and diverse properties, all follow. This hypothesis points to the direction one must look for a microscopic theory of the phenomena in Cu-O compounds. The proposed excitation spectrum is also shown to lead us to an attractive contribution to the electron-electron interaction in the s-wave channel