Band-structure and core-hole effects in resonant inelastic soft-x-ray scattering: Experiment and theory

Inelastic x-ray scattering has been observed in the hexagonal forms of carbon (graphite) and boron nitride (hBN), both above and below their K edges. For excitation energies below the core threshold, inelastic-loss features are observed, which disperse linearly with excitation energy (Raman-like behavior). However, above the threshold, emission features that move in a nonlinear fashion are observed. We show that these two scattering regimes, which have previously been thought of as separate processes, viz,, resonant x-ray Raman scattering (below threshold) and resonant inelastic x-ray scattering (above threshold), are described by the same theory for resonant fluorescence. Simulated spectra, with and without excitonic effects, are presented and compared with experiment. We conclude, based on this comparison, that excitonic effects influence these spectra in two ways. Primarily, the total fluorescence yields are enhanced or reduced simply because of changes in the absorption cross sections. Second, excitonic effects on emission features can be pronounced near some excitonic resonances, and these changes are more significant for excitation further above the K edges, which we attribute to the multiplicity of core-excited states being probed. Based on these findings, we conclude that core-hole effects do not necessarily undermine an interpretation of the scattering in terms of a one-electron (noninteracting) picture, and that resonant fluorescence spectroscopy may be successfully used to probe the band structure of solids. [S0163-1829(99)08911-0].