Dynamical spin susceptibility in La2CuO4 studied by resonant inelastic x-ray scattering

Resonant inelastic x-ray scattering (RIXS) is a powerful probe of elementary excitations in solids. It is now widely applied to study magnetic excitations. However, its complex cross section means that RIXS has been more difficult to interpret than inelastic neutron scattering (INS). Here we report similar to 37 meV resolution RIXS measurements of the magnetic excitations in La2CuO4, the antiferromagnetic parent of one system of high-temperature superconductors. At high energies (similar to 2 eV), the RIXS spectra show angular-dependent dd orbital excitations in agreement with previous RIXS studies but show new structure. They are interpreted with single-site multiplet calculations. At low energies (less than or similar to 0.3 eV), we model the wave-vector-dependent single magnon RIXS intensity as the product of the calculated single-ion spin-flip RIXS cross section and the dynamical structure factor S(Q, omega) of the spin-wave excitations. When S(Q, omega) is extracted from our data, the wave-vector-dependence of the single-magnon pole intensity shows a similar variation to that observed by INS. Our results confirm that suitably corrected RIXS data can yield the genuine wave-vector and energy dependence of S( Q,.) for a cuprate antiferromagnet. In addition to spin waves, our data show structured multimagnon excitations with dispersing peaks in the intensity at energies higher than the single-magnon excitations.

Automated summary

RIXS is a powerful probe for studying elementary excitations in solids, particularly magnetic excitations. This study reports the measurement of magnetic excitations in La2CuO4 using RIXS with high resolution and complex interpretation. The results confirm the genuine wave-vector and energy dependence of S(Q,.) for a cuprate antiferromagnet, showing structured multi-magnon excitations with dispersing peaks in addition to single-magnon excitations.