High-energy spin and charge excitations inLa2CuO4

Inelastic light scattering studies of ${\mathrm{La}}_2$ ${\mathrm{CuO}}_4$, both pure and doped with lead, over the energy range 0–1 have revealed the presence of high-frequency $A_{1g}$ scattering components, in the spectral region 3500–6000 ${\mathrm{cm}}^{\mathrm{-}1}$, while also providing the complete line shape for the previously reported spin-pair mode of $B_{1g}$ symmetry. Two main bands, broad and overlapping, are observed in this region with maxima near 3500 and 5200 ${\mathrm{cm}}^{\mathrm{-}1}$. The various spectral features show different resonance behavior. We suggest that a model based upon coupled spin and charge excitations will be required to describe these spectra.