  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 which possess the same energy scale and doping dependence as
previously observed by Raman spectroscopy. They disperse weakly in
energy-momentum space, and are consistent with a bimagnon dispersion that is
renormalized by the magnon-magnon interaction at the zone center.
