Pseudogaps in the van Hove Jahn-Teller scenario

The van Hove scenario can provide a unified framework for understanding many of the anomalous superconducting and normal-state properties of the high-T-c cuprates. The present paper will review evidence for a novel form of electron-phonon coupling associated with splitting the degeneracy of two van Hove singularities (vHs): a van Hove Jahn-Teller (JT) effect. The JT distortions can give rise to dynamical local tilting and breathing modes, and the onset of the instability will appear as a pseudogap phase. The local breathing mode excitations give rise to large polaronic effects. In particular, there can be large polaronic band renormalizations, but only in the vicinity of a vHs-even when the vHs is away from the Fermi level. This can provide an explanation for the ''extended vHs'' observed in the cuprates.