Chapter 198 Neutron scattering studies of spin fluctuations in high-temperature superconductors

Abstract

Publisher Summary This chapter describes the neutron scattering studies of the spin fluctuations in the CuO2 planes. The rare earths that form an important constituent of almost all high-Tc materials are viewed as somewhat passive spectators. The fact that many candidate theories of high-temperature superconductivity include spin fluctuations as a central feature of the mechanism for superconductivity increases the importance of obtaining a detailed picture of the energy, momentum, temperature, and doping dependence of the magnetic dynamics of the cuprates. Many of the anomalous normal-state properties of the doped cuprates are likely related to the proximity of antiferromagnetism in the phase diagram and the manifestation of this instability in the excitations. Even in the absence of a magnetic mechanism for high temperature superconductivity, the spin fluctuations are an important degree of freedom of the quasi particles that form the superconducting condensate, and therefore a probe of the nature of that transition. The properties of a magnetic system close to instability such as an antiferromagnetic ordering transition are characterized by divergences in various physical properties. Neutron scattering can access several of the important parameters through the energy integrated cross-section or critical scattering, which is proportional to the Fourier transform of the instantaneous spin–spin correlation function.