Resonant inelastic X-ray scattering study of spin-wave excitations in the cuprate parent compound Ca2CuO2Cl2

By means of resonant inelastic x-ray scattering at the Cu L3 edge, we measured the spin wave dispersion along 100 and 110 in the undoped cuprate Ca2CuO2Cl2. The data yields a reliable estimate of the superexchange parameter J = 135 ± 4 meV using a classical spin-1/2 2D Heisenberg model with nearest-neighbor interactions and including quantum fluctuations. Including further exchange interactions increases the estimate to J = 141 meV. The 40 meV dispersion between the magnetic Brillouin zone boundary points (1/2, 0) and (1/4, 1/4) indicates that next-nearest neighbor interactions in this compound are intermediate between the values found in La2CuO4 and Sr2CuO2Cl2. Owing to the low-Z elements composing Ca2CuO2Cl2, the present results may enable a reliable comparison with the predictions of quantum many-body calculations, which would improve our understanding of the role of magnetic excitations and of electronic correlations in cuprates.