A comparison between charge-transfer and sliding-bond models for superconduction in YBCO cuprate

Recently a model for electron-pairing in unconventional superconductors has been proposed. It maintains that in cuprates delocalized electron-bonds are formed between contiguous layers of copper oxide. This model, which we name the ''sliding-bond'' model, reutilizes the BCS scheme, but with a kind of electron pairs quite different from Cooper's pairs [Brovetto et al., Eur. Phys. J. B 17,85 (2000); Brovetto et A, submitted]. In this paper, considering the case of YBCO cuprate, some features of the model spoken of are compared with those of the charge-transfer model [Cava et al., Physica C 165, 419 (1990); Jorgensen, Phys. Today 44, 34 (1991)]. It is shown that, according to both models, the decrease in the YBCO critical temperature when oxygen is removed is originated by the decrease in the charge of copper ions lying on the superconducting planes.