Abstract
Coupling of excitations leads to intriguing effects on the spectra of materials. We propose a cumulant formulation for neutral electronic excitations which opens the way to describe effects such as double plasmon satellites or exciton-exciton coupling. Our approach starts from the GW + Bethe-Salpeter approximation to many-body perturbation theory which is based on a quasiparticle picture, and it adds coupling of excitations through a consistent inclusion of dynamically screened interactions. This requires one to consider scattering contributions that are usually neglected. The result is formulated in a way that highlights essential physics, that can be implemented as a postprocessing tool in first-principles codes, and that suggests which kind of materials and measurements should exhibit strong effects. This is illustrated using a model.
Highlights
Correlation satellites in optical and loss spectraPierluigi Cudazzo and Lucia Reining 3,2 1Physics and Materials Science Research Unit, University of Luxembourg, 162a Avenue de la Faïencerie, L-1511 Luxembourg, Luxembourg 2European Theoretical Spectroscopy Facility (ETSF) 3Laboratoire des Solides Irradiés, École Polytechnique, CNRS, CEA/DRF/IRAMIS, Institut Polytechnique de Paris, F-91128 Palaiseau, France (Received 22 June 2018; revised manuscript received November 2019; accepted November 2019; published 6 February 2020)
Coupling of excitations leads to intriguing effects on the spectra of materials
We propose a cumulant formulation for neutral electronic excitations which opens the way to describe effects such as double plasmon satellites or exciton-exciton coupling
Summary
Pierluigi Cudazzo and Lucia Reining 3,2 1Physics and Materials Science Research Unit, University of Luxembourg, 162a Avenue de la Faïencerie, L-1511 Luxembourg, Luxembourg 2European Theoretical Spectroscopy Facility (ETSF) 3Laboratoire des Solides Irradiés, École Polytechnique, CNRS, CEA/DRF/IRAMIS, Institut Polytechnique de Paris, F-91128 Palaiseau, France (Received 22 June 2018; revised manuscript received November 2019; accepted November 2019; published 6 February 2020). To lowest order in W electron addition and removal spectra are obtained in the widely used GW approximation for the electron self-energy [8] This reflects a picture of a quasiparticle coupled to neutral charge excitations, which create satellites because W (ω) is frequency dependent. The spectrum of these excitations, and W , can in turn be obtained by solving the two-particle BetheSalpeter equation (BSE) for the irreducible polarizability P, where the dressed electrons and holes interact to lowest order through the dynamically screened W itself [7,9]. It is the exact solution for a two-level limiting case [44], and it is motivated by the success of an increasing number of ab initio calculations for the one-body G using a cumulant of first order in W [37,41,44,45,46] while higher order contributions appear to be negligible [47,48,49]
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