The barium giant dipole resonance in barite: a study of soft X-ray absorption edges using hard X-rays

Giant dipole resonances are collective phenomena which can be found in systems ranging from atoms through clusters to solids. In atomic and solid state physics such excitations are usually studied by soft X-ray absorption, photoelectron and electron energy-loss spectroscopies. With the advent of third-generation synchrotron radiation sources, nonresonant inelastic X-ray scattering became a prominent tool to study truly bulk sensitive shallow absorption edges with high energy photons. The method is not limited to measuring dipole transitions but allows the study of final states of different symmetry due to monopole and quadrupole transitions employing its momentum-transfer dependence. In this paper the potential of nonresonant inelastic X-ray scattering to probe low-energy excitations is emphasized with the focus on symmetry selectivity, study of liquids and high pressure applications. As an example, nonresonant inelastic X-ray scattering spectra of the barium 4d-f giant dipole resonance in barite are discussed.