Correlated photoemIssion spectra from the three-body Green’s function – COLIBRI

In this project we propose to formulate, implement and apply a novel theory for the description of correlated photoemission spectra (PES) based on the three-body Green’s function. Photoemission is a unique source of information about electronic structure and excitations in materials. Theory represents an essential tool for the analysis of the experiments as well as prediction of material properties. Moreover, the correct description of the electronic structure is essential for modelling more advanced experiments. State-of-the art methods for the description of PES are based on the one-body Green’s function, which describes the propagation of a single particle into the system; the interaction with the other particles of the system is taken into account through an effective potential which needs to be approximated. Standard approximations work well for the quasiparticle part (energy of the particle added to the system) of the spectrum in weakly and moderately correlated systems, such as metals and standard semiconductors (e.g., Si or GaAs), but not for satellite features which are related to other excitations of the system, such as e.g. plasmons (linked to neutral excitations induced by the added particle). Moreover, they completely fail for most strongly correlated systems, which are of paramaount importance both from the scientific and technological point of view. We hence propose to formulate a novel theory of correlated photoemission spectra using the three-body Green’s function, which describes the propagation of three particles, and which can hence treat on an equal footing quasiparticles and satellites (electron-hole pairs). We will first validate our approach on exactly solvable models and then implement it in the open-source YAMBO code. Our strategy can also we extended to more exotic excitations, such as trions, a localized excitation which consists of three charged particles, or to photoemission spectra of systems with excitons.