Electron-phonon coupling in high temperature superconductors: The connection to superconducting behavior

Abstract

Abstract The results of recent calculations of the frequency, linewidths, and coupling strengths to carriers on the Fermi surface for several phonons in La1.85Sr0.15CuO4 (LSCO) [our work] and YBa2Cu3O7 (YBCO) [by the Stuttgart group] are discussed and related to experiment. The estimates of the electron-phonon coupling constant are X = 1.35 for LSCO based on 11 phonons, and λ = 1.7 for YBCO based on 17 phonons. These coupling strengths are large enough to make the electron-phonon interaction a central feature in normal state transport properties and a likely candidate for the pairing mechanism for high temperature superconductivity. The strong coupling arises from features that are generic in the high temperature superconducting cuprates: a modest (certainly not large) density of states at the Fermi level which results in weak screening; a confinement of the metallic electrons to layers separated by dielectric regions, which further weakens screening and results in Madelung-like contributions to electron-phonon matrix elements; the site energies of the Cu d states and the O p states are roughly equal, leading to strong hybridization and highly metallic bands at the Fermi level.