A possible mechanism of high $T_c$ superconductivity involving biexcitons

A new mechanism for high $T_c$ superconductors involving biexcitons resulting from the possible electronic polarization of the surrounding medium in which $Cu-O$ layers are embedded is proposed. It is a variant of the correlated charge (pair) transfer mechanism proposed by Sinha and Singh recently. It is argued that this process may take precedence over the correlated charge transfer (pair) mechanism if the energies of the states of the complex $O^{2-}-Cu^{3+}-O^{2-}$ and $O^{1-}-Cu^{+1}-O^{-1}$ are nearly degenerate