Constraints imposed by the data on a successful theory of high-temperature superconductivity

Abstract

Data for high-temperature superconductivity are analyzed in order to determine the required nature of a successful general theory of oxide superconductivity. (1) The p-type nature of high-temperature superconductivity requires a model based on oxygen. (2) Since ideal (Rare- earth) Ba 2 Cu 3 O 7 compounds superconduct at approximately equals 92 K even for magnetic rare-earth ions, but the same compounds do not superconduct when many of the same magnetic ions occupy Ba-sites, the superconductivity must originate in the charge-reservoir region, not in the cuprate planes. (3) The recent observation of photo-induced superconductivity in YBa 2 Cu 3 O x , but not in La 2 CuO 4 , indicates the importance of charge-balance and whether the dopant oxygen is interstitial or substitutional. (4) Pair-breaking data require that a successful model be three-dimensional. (5) The observation of granular superconductivity in PrBa 2 Cu 3 O 7 requires a successful model to be inhomogeneous. (6) Many data require that the superconductivity originate in charge-reservoirs, rather than in cuprate planes. The following classes of models are ruled out: (1) Cu +2 ↔Cu +3 valence fluctuations models; (2) spin-fluctuation and d-wave pairing models; (3) hybridization and t-J models of the insulating nature of PrBa 2 Cu 3 O 7 ; (4) all models based on the charge-transfer hypothesis; (5) all two- dimensional models; and (6) all homogeneous models.