Lattice instability due to carrier-phonon coupling in high-Temperature superconductors

Abstract

Based on the experiments such as Raman scattering and far-infrared spectra, it is assumed that carriers, Zhang-Rice singlets formed at low doping level in the CuO 2 plane, strongly couple with phonons associated with the planar O(2) or O(3). By taking into account the coupling effect on the transfer integral energy between CuO 4 units in the CuO 2 plane, an effective Hamiltonian for this system is established. Like one-dimensional Peierls transition, the appearance of soft-phonon modes of O(2) or O(3) causes a lattice instability that opens a pseudogap over the Fermi surface and produces a static displacement of O(2) or O(3) along C axis. The transition temperature are estimated from the model Hamiltonian. The conclusions are in accord with the experiments.