Resonant inelastic x-ray scattering beyond the quasiparticle approximation*

Resonant inelastic x-ray scattering (RIXS) provides unprecedented experimental access to the fundamental excitations and dynamical responses of correlated materials. Recently, first-principle methods, e.g. based on solving the Bethe-Salpeter equation (BSE), have succeeded in calculating the quasiparticle contribution to RIXS that reflects the underlying band-structure.  However, this neglects the important contribution of secondary excitations that are the signatures of the correlated response of the probed material.  We significantly improve the BSE description of RIXS by invoking a quasiboson model to describe these secondary excitations in a manner akin to the classic theory of Mahan, Nozières & Dominicis [1,2]. We generate the quasiboson excitation spectrum (e.g. plasmons and secondary electron-hole pairs) through a real-time time-dependent density functional theory calculation of the charge density response to the initial core-level excitation. Our new methodology succeeds at accurately reproducing the experimental RIXS spectrum at the Fe L3 edge of the benchmark correlated metal BaFe₂As₂, including both quasiparticle and correlated contributions [3].

 

[1] Mahan, Phys Rev 163, 612 (1967).

[2] Nozières & de Dominicis, Phys Rev 178, 1097 (1969).

[3] Gilmore et al., Phys Rev X 11, 031013 (2021).