We show that doping-induced charge fluctuations in strongly correlated Hubbard electron systems near the 1/2-filled, insulating limit cause overscreening of the electron-electron Coulomb repulsion. The resulting attractive screened interaction potential supports d_{x^2-y^2}-pairing with a strongly peaked, doping dependent pairing strength at lower doping, followed by s-wave pairing at larger doping levels.
@article{arxiv.cond-mat/9805133,
title = {Overscreening in Hubbard electron systems},
author = {H. -B. Schüttler and C. Gröber and H. G. Evertz and W. Hanke},
journal= {arXiv preprint arXiv:cond-mat/9805133},
year = {2007}
}