Charge transfer excitations and superconductivity in "ionic" metals

Abstract

The newly discovered high Tc oxide metals have a low enough electron density that the charge transfer excitations between the nearest neighbor cations and anions are unscreened. Excitonic resonances with large oscillator strengths are then possible. It is suggested that the high Tc is due to scattering of electrons from such resonances rather than from photons. © 1993.