CONSTRAINTS ON SUPERCONDUCTING TRANSITION-TEMPERATURES IN THE CUPRATES - ANTIFERROMAGNETIC SPIN FLUCTUATIONS

Recently, several authors have suggested that antiferromagnetic spin fluctuations provide the pairing mechanism in the high-temperature superconductors. In this paper, we discuss this spin-fluctuation mechanism in the Fermi-surface-restricted Eliashberg formalism using a dynamical susceptibility whose form is constrained by neutron-scattering data. For definiteness, we consider the YBa2Cu3O7-delta family of superconductors, which we model with a realistic model band structure. Furthermore, we choose the electron-spin fluctuation coupling constant lambda to yield agreement with low-frequency ac conductivity measurements. We find that spin-singlet pairing can occur only for B1 and A2 symmetries and that the former symmetry yields the higher critical temperature T(c). The T(c) associated with the B1 symmetry is large in the weak-coupling limit, but is greatly reduced when strong-coupling effects are included. Finally, we observe that even for anisotropic pairing schemes, transport data that constrain lambda provide stringent limits on the critical temperature.