Phonon mechanism of high-temperature superconductivity

The majority opinion on the origin of high-temperature superconductivity is that it is a purely electronic phenomenon involving spins, and phonons are irrelevant to the mechanism. However, such a view is based upon the knowledge of the phonon mechanism in simple metals, while the cuprates are much more complex due to various competing forces. We suggest that the electron-phonon coupling in the cuprates is significantly different because of their covalency, ionicity and strong electron correlation. In particular phonon-induced intersite charge transfer creates a strong electron-phonon coupling that is dependent on mode and wavevector, and could form a basis for phonon mechanism of high-temperature superconductivity.