Neutron scattering from magnetic excitations in Bi2Sr2CaCu2O8+δ

Many of the physical properties of the copper oxide high-temperature superconductors appear to defy the conventional ‘one-electron’ theory of metals. The development of alternative theories incorporating strong electron correlations is currently at the forefront of research in condensed-matter physics. In this context, inelastic neutron scattering can provide valuable insight into collective magnetic excitations in the copper oxide superconductors and so guide these theoretical efforts. Such measurements require large single crystals, and have hitherto been restricted to just two families of high-temperature superconductors—La2−xSrxCuO4 (ref. 1) and YBa2Cu3O6+x (ref. 2). Although the magnetic spectra of these two materials bear certain similarities, there are also important differences. In particular, a sharpresonant spin excitation dominates the spectrum in the superconducting state of YBa2Cu3O6+x (3–10), but is not observed in La2−xSrxCuO4 (ref. 1). Here we report inelastic neutron scattering measurements of a different copper oxide system—Bi2Sr2CaCu2O8+δ—in which we observe a magnetic resonance peak in the superconducting state. This result implies that this excitation phenomenon is a general feature of the copper oxide superconductors, so extending the empirical basis for its theoretical description.