Dilute Annealed Magnetism and High Temperature Superconductivity

It has become increasingly appreciated that the strong antiferromagnetic coupling between in-plane Cu atoms in most of the high-temperature superconductors is not merely fortuitous [ 1-4 ]. However a coherent understanding of exactly how the magnetic interactions influence the observed superconductivity has been elusive. Here we focus on the prototype compound, La2_xSrxCuO 4 ( " 2 1 4 " ) . We present calculations suggesting that the BCS parameter 2 scales with the effective strength of the magnetic interactions, and that these weaken with progressive dilution. In particular, we show that this decrease of magnetic interactions produces the characteristic decrease of the curve Tc(x) with x, where 0 < x < 2 is the number of ferromagnetic bonds per plaquette. We begin by considering the BCS equation in the weak coupling limit [ 5 ],