Resonant inelastic x-ray scattering studies of magnons and bimagnons in the lightly doped cuprate La 2 − x Sr x CuO 4

Abstract : We investigated the doping dependence of magnetic excitations in the lightly doped cuprate La2−xSrxCuO4 via combined studies of resonant inelastic x-ray scattering (RIXS) at the Cu L3 edge and theoretical calculations. With increasing doping, the magnon dispersion is found to be essentially unchanged, but the spectral width broadens and the spectral weight varies differently at different momenta. Near the Brillouin zone center, we directly observe bimagnon excitations that possess the same energy scale and doping dependence as previously observed by Raman spectroscopy. They disperse weakly in energy-momentum space, and they are consistent with a bimagnon dispersion that is renormalized by the magnon-magnon interaction at the zone center.