Spin fluctuations and $d_{x^2-y^2}$ pairing in the high temperature superconductors

Özet

I present an overview of the theoretical basis and experimental evidence for the proposal that the magnetic interaction between planar quasiparticles in the cuprate superconductors is responsible for both their anomalous normal state behavior and their transition at high temperatures to a superconducting state with $d_{x^2-y^2}$ pairing. I discuss information on the magnetic interaction obtained from NMR and neutron experiments, and show how the momentum dependence of this interaction leads naturally both to $d_{x^2-y^2}$ pairing and to the measured transport properties and the description of $YBa_2 Cu_3 O_7$ as a nearly antiferromagnetic Fermi liquid. The quite different influence of Zn and Ni planar impurities on $T_c$ is shown to provide a "smoking gun" for the magnetic mechanism. In conclusion, I review the experimental evidence for the inseparability of spin and charge behavior in the underdoped cuprates and discuss the phase diagram for the normal state which makes evident the connection between the opening of the quasiparticle pseudogap and pseudoscaling behavior and enables one to deduce the antiferromagnetic correlation length from NMR measurements of the 63 Cu spin-lattice relaxation rate.