Resonant inelastic soft x-ray scattering of Be chalcogenides

The bulk electronic band structures of BeTe and BeSe have been studied by resonant inelastic soft x-ray scattering (RIXS) at the Be 1s edge. We derive direct and indirect bulk band gaps and observe the coexistence of core excitons and momentum conservation. A quantitative analysis of the coherent spectral fraction gives insight into the femtosecond time scale of the relevant dephasing processes. Experimental results agree very well with calculations based on the Kramers-Heisenberg and density-functional theories.