Recent inelastic neutron scattering (INS) experiments on La2−xSrxCuO4 observed a {\it magnetic coherence effect}, i.e., strong frequency and momentum dependent changes of the spin susceptibility, χ′′, in the superconducting phase. We show that this effect is a direct consequence of changes in the damping of incommensurate antiferromagnetic spin fluctuations due to the appearance of a d-wave gap in the fermionic spectrum. Our theoretical results provide a quantitative explanation for the weak momentum dependence of the observed spin-gap. Moreover, we predict {\bf (a)} a Fermi surface in La2−xSrxCuO4 which is closed around (π,π) up to optimal doping, and {\bf (b)} similar changes in χ′′ for all cuprates with an incommensurate magnetic response.
@article{arxiv.cond-mat/0004220,
title = {Magnetic Coherence in Cuprate Superconductors},
author = {Dirk K. Morr and David Pines},
journal= {arXiv preprint arXiv:cond-mat/0004220},
year = {2009}
}