Measurement of Magnetic Excitations in the Two-Dimensional AntiferromagneticSr2CuO2Cl2Insulator Using Resonant X-Ray Scattering: Evidence for Extended Interactions

Abstract

We measured the momentum dependence of magnetic excitations in the model spin-$1/2$ 2D antiferromagnetic insulator ${\mathrm{Sr}}_2{\mathrm{CuO}}_2{\mathrm{Cl}}_2$ (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 $t\mathrm{\text{-}}{t}^{\prime }\mathrm{\text{-}}{t}^{\prime \prime }\mathrm{\text{-}}U$ 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. DOI: http://dx.doi.org/10.1103/PhysRevLett.105.157006 © 2010 The American Physical Society