Symmetry and Intervalent Charge Transfer in Copper‐Oxide Superconducting Precursors

Abstract

AbstractA vibrationally coupled intervalent charge transfer theory is proposed for the copper oxide‐superconductors. The proposed B1g‐vibrational distortion exactly interchanges the chemical environment of the neighboring copper atoms. A quadruple cell is constructed to accommodate the non‐stoichiometry and a double copper‐oxide‐conducting chain with distorted symmetry is postulated. The distorted structure, prone to switching of the copper sites by vibration, is postulated to be the superconducting precursor. The left over‐oxygen, due to oxygen deficiency, is allowed to serve as a bridge between the chains and 10 oscillate with the vibration. Symmetry of the system, before and after distortion, is used to explain the spin‐angular momentum change, needed to arrive at Cooper‐paired electron/holes. The O− and O= atoms are postulated to be the bridge for superexchange and charge flow between the Cu+1/Cu+3 and Cu+1/Cu+2 pairs. The same theory is used to interpret the mechanisms for the following three types of copper oxide‐superconductors: YBa2Cu3OT‐x; La2‐xSrxCuO4 and the newly discovered electron superconductor Nd2‐xCexCuO4‐y. The bridge oxygen oscillation may be chosen not to come from the breathing mode but from the bending deformation mode that involves the relative motion of the Cu atoms (to the oxygen) giving rise to smaller oxygen isotope effect.