We 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.
Nicola Marzari, Iurii Timrov, Eric Macke
Nicola Marzari, Luca Binci, Davide Grassano