Singlet superconductivity in a two-band model

A pairing mechanism between an extra hole localized around the O atom and the hole already present on the Cu atom in the undoped La 2 Cu O 4 compounds is discussed. A stable superconductivity state appears below a critical temperature T c. The model includes only the singlet terms of interaction. The transition temperature depends on a characteristic parameter which is the modified Fermi level in the doped compounds of Lanthanum. The analytical results are similar to those of the BCS theory, with peculiarities corresponding to the electronic nature of the interaction. (Author)