Quasiparticle Lifetime Broadening in Resonant X-ray Scattering of Ammonium Nitrate
John Vinson, Terrence J. Jach, Matthias Mueller, Rainer Unterumsberger, Burkhard Beckhoff
It has been previously shown that two effects cause dramatic changes in the x-ray absorption and emission spectrra from the N K edge of the insulating crystal ammonium nitate. 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 anomously large broadening ($\sim\,$4eV) of the emission originating from $\sigma$ states in the nitrate band 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 progressivley reduced toward the N edge. Using a \it GW}/Bethe-Salpeter approach, we show the extent to which this anomolous broadening is captured by the \it GW} approximation. 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 in $\sigma$ states of other related compounds.
, Jach, T.
, Mueller, M.
, Unterumsberger, R.
and Beckhoff, B.
Quasiparticle Lifetime Broadening in Resonant X-ray Scattering of Ammonium Nitrate, Physical Review B, [online], https://doi.org/10.1103/PhysRevB.94.035163, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=919907
(Accessed September 27, 2023)