Spin-fluctuation-induced superconductivity: Mythsvs. reality

Abstract

We consider several scientific myths associated with the role played by spin fluctuations in the copper oxide superconductors and report on recent theoretical and experimental work which confronts the myths with reality and, in so doing, effectively destroys them. Among the myths we expose are: «spin fluctuations cannot bring abouthigh-temperature superconductivity»; «even if spin fluctuations can bring about highTc, the coupling constant required is so large that the corresponding normal-state properties will not agree with experiment»; «experiment suggests that the pairing state is “s”-wave or extendeds-wave». We report on the results of strong-coupling calculations using the Eliashberg formalism which provide strong evidence for the description of the planar quasi-particles in YBa2Cu3O7 as a nearly antiferromagnetic Fermi liquid in which the measured anomalous normal-state properties arise from the coupling of quasi-particles to spin fluctuations, while their spin-fluctuation-induced interaction leads uniquely to a superconducting state withdx2−y2 symmetry. We survey briefly a number of recent experimental developments on the superconducting properties of YBa2Cu3O7 which argue strongly againsts-wave pairing, while lending support to adx2−y2 pairing state.