title: Quasiparticle Lifetime Broadening in Resonant X-ray Scattering of NH4NO3.
abstract: It has been previously shown that two effects cause dramatic changes in the x-ray absorption and emission spectra from the N K edge of the insulating crystal ammonium nitrate. First, vibrational disorder causes major changes in the absorption spectrum, originating not only from the thermal population of phonons, but, significantly, from zero-point motion as well. Second, the anomalously large broadening (~4 eV) of the emission originating from nitrateσstates is due to unusually short lifetimes of quasiparticles in an otherwise extremely narrow band. In this work we investigate the coupling of these effects to core and valence excitons that are created as the initial x-ray excitation energy is progressively reduced toward the N edge. Using aGW/Bethe-Salpeter approach, we show the extent to which this anomalous broadening is captured by theGWapproximation. The data and calculations demonstrate the importance that the complex self-energies (finite lifetimes) of valence bands have on the interpretation of emission spectra. We produce a scheme to explain why extreme lifetimes should appear inσstates of other similar compounds.
authors.affiliation: Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899.
authors.forename: John
authors.initials: J
authors.lastname: Vinson
authors.affiliation: Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899.
authors.forename: Terrence
authors.initials: T
authors.lastname: Jach
authors.affiliation: Physikalisch-Technische Bundesanstalt, Abbestraße 2-12, 10587 Berlin, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Müller
authors.affiliation: Physikalisch-Technische Bundesanstalt, Abbestraße 2-12, 10587 Berlin, Germany.
authors.forename: Rainer
authors.initials: R
authors.lastname: Unterumsberger
authors.affiliation: Physikalisch-Technische Bundesanstalt, Abbestraße 2-12, 10587 Berlin, Germany.
authors.forename: Burkhard
authors.initials: B
authors.lastname: Beckhoff