  Thanks to high resolution and polarization analysis, resonant inelastic x-ray
scattering (RIXS) magnetic spectra of La2CuO4, Sr2CuO2Cl2 and CaCuO2 reveal a
rich set of properties of the spin 1/2 antiferromagnetic square lattice of
cuprates. The leading single-magnon peak energy dispersion is in excellent
agreement with the corresponding inelastic neutron scattering measurements.
However, the RIXS data unveil an asymmetric lineshape possibly due to odd
higher order terms. Moreover, a sharp bimagnon feature emerges from the
continuum at (1/2,0), coincident in energy with the bimagnon peak detected in
optical spectroscopy. These findings show that the inherently complex spin
spectra of cuprates, an exquisite manifestation of quantum magnetism, can be
effectively explored by exploiting the richness of RIXS cross sections.
