Strongly correlated electrons and neutron scattering

Various aspects of the close and interesting relationship between antiferromagnetism and singlet ground states are presented for which neutron scattering play vital roles. Special emphasis is laid on the disorder-induced antiferromagnetism in spin-Peierls systems, which can be viewed as a nucleation process of classical magnetic order in the background of the singlet state whose origin is purely quantum-mechanical. It is then pointed out that similar features will be found in CexCu2Si2 and high T-c cuprates, Finally the possible charge ordering process in NaV2O5 is discussed which leads to the quenching of localized spins. (C) 1999 Elsevier Science Ltd. All rights reserved.