Guarise, M.Dalla Piazza, B.Sala, M. MorettiGhiringhelli, G.Braicovich, L.Berger, H.Hancock, J. N.van der Marel, D.Schmitt, T.Strocov, V. N.Ament, L. J. P.van den Brink, J.Lin, P.-H.Xu, P.Ronnow, H. M.Grioni, M.2011-03-162011-03-162011-03-16201010.1103/PhysRevLett.105.157006https://infoscience.epfl.ch/handle/20.500.14299/65362WOS:000282683500008We measured the momentum dependence of magnetic excitations in the model spin-1/2 2D antiferromagnetic insulator Sr2CuO2Cl2 (SCOC). We identify a single-spin-wave feature and a multimagnon continuum, with different polarization dependences. The spin waves display a large (70 meV) dispersion between the zone-boundary points (pi, 0) and (pi/2, pi/2). Employing an extended t-t'-t ''-U one-band Hubbard model, we find significant electronic hopping beyond nearest-neighbor Cu ions, indicative of extended magnetic interactions. The spectral line shape at (pi, 0) indicates sizable quantum effects in SCOC and probably more generally in the cuprates.Lamellar Copper OxidesSquare-LatticeHeisenberg-AntiferromagnetOptical-PropertiesRaman-ScatteringSpectraLa2Cuo4Statetext::journal::journal article::research article