Giant defect-enhanced electron-phonon interactions in ternary copper oxide superconductors

A microscopic but schematic model is discussed for defects (such as oxygen vacancies O^) in compounds such as YBa₂{Cu}₃O_7+δ{O}_{2{{-}}{{δ}}}^{{{}}}$ and ${La}_{3{{-}}x}Ba₃₊ₓ{Cu}₆O_14-δ{O}_{4{{-}}{{δ}}}^{{{}}}$ in relation to the superconductive properties of these materials. The discussion shows in detail how ${T}c$ can reach its maximum value at or near the metal-semiconductor transition ${T}ₘₛ$. It introduces a new mechanism for enhancing of electron-phonon interactions that is separate from, and empirically superior to, Fermi-surface nesting.