Raman Scattering from Spin Fluctuations in the Cuprates
Following the discovery of the new class of oxide superconductors in 19871 some workers rapidly suggested a possible link between the magnetic properties of the systems and their superconducting properties.2 The cuprate systems are unique in that they exhibit a square planar lattice of copper spins, with spin 1/2, coupled by superexchange via the oxygen atoms. Although the earliest of these ideas have since been shown to be inapplicable to the specific systems involved, it is still true that a detailed understanding of the superconducting mechanism has remained elusive, and much interest is centered on the possibility that magnetic phenomena may lie at the heart of the pairing mechanism. In this context, it has become important to understand the magnetic behavior of both the parent and superconducting systems, in hopes of shedding light on the mechanism of the superconductivity. As these studies have progressed, it has become clear that the magnetic system itself, described by a Heisenberg 2D antiferromagnetic interaction for the insulators, is not amenable to description in terms of previous theoretical results. The first portion of this paper is devoted to a report of these deficiencies, especially as they are reflected in the spin dynamics seen through inelastic light scattering, and the manner in which they may be resolved. This problem has taken on interest in its own right, independent of its relation to superconductivity. As we shall show, the conventional spin wave theory fails to describe the short wavelength dynamics for these systems, and must be supplanted by a treatment which takes explicit account of quantum fluctuations in the ground state.
KeywordsSpin Dynamic Quantum Fluctuation Spin Fluctuation Spectral Moment Previous Theoretical Result
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