Dx2 − y2 Pairing and spin fluctuations in the cuprate superconductors: A progress report

Abstract

We present a simple model calculation of the superconducting pairing potential which makes evident the causal relationship between an effective magnetic interaction between planar quasiparticles which is peaked in momentum space at Q = π a , π a , and their transition to a superconducting state with d x 2 − y 2 pairing. We review recent experimental and theoretical developments which establish the common physical origin of scaling behavior and the spin pseudogap in underdoped systems and consider non-linear feedback effects which could give rise to this behavior in a nearly antiferromagnetic Fermi liquid. We discuss the shortcomings of the present generation of Hubbard model calculations in providing a quantitative account of the normal state magnetic and transport properties, as well as of T c , and suggest that apart from the SQUID experiments which probe directly the symmetry of the pairing state, measurements of the spin-lattice relaxation times, 63 T 1 and 17 T 1 and the spin-echo decay time, 63 T 2 G , provide the strongest constraints to date on candidate pairing states. We conclude with a qualitative discussion of the predictions of the magnetic mechanism for the doping dependence of T c .