Van Hove Exciton-Cageons and High-T${}_c$ Superconductivity: XB: Polaronic Coupling in the Doped Material

Abstract

A purely ionic interpretation of the tilting mode instabilities in La${}_{2-x}$A${}_x$CuO${}_4$ (A=Sr,Ba) is shown to be not self-consistent: the dominant factor influencing the doping dependence of the interlayer mismatch is the large change in the Cu-O bond length, which in turn leads to a strong electron-phonon coupling. This coupling is closely related to the vHs-JT effect. This new insight clarifies the role of the tilt-mode instabilities. The main JT coupling is {\it not} to these modes, but to the in-plane O-O bond stretching modes which split the vHs degeneracy. However, as these modes soften, they couple to the lower-lying tilt modes, so that the ultimate instability has a finite tilt component. The bond stretch modes have a large, linear coupling to electrons, with clear polaronic effects. A striking result of this is that there will be a large polaronic band narrowing near the vHs, whether or not the vHs is near the Fermi level. This vHs-localized band narrowing provides a natural explanation for the common occurence of extended vHs's.

22 pages RevTeX, 7 figures available upon request

References in corpus (4)

• The Electron-Phonon Interaction in the Presence of Strong Correlations
• Van Hove Exciton-Cageons and High-T${}_c$ Superconductivity: VIIID Solitons and Nonlinear Dynamics
• Van Hove Excitons and High-T${}_c$ Superconductivity: VIIIC Dynamic Jahn-Teller Effects vs Spin-Orbit Coupling in the LTO Phase of La${}_{2-x}$Sr${}_x$CuO${}_4$
• Van Hove Exciton-Cageons and High-T${}_c$ Superconductivity, XA: Role of Spin-Orbit Coupling in Generating a Diabolical Point

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• Flux Phase as a Dynamic Jahn-Teller Phase: Berryonic Matter in the Cuprates?