Photoemission Beyond the Sudden Approximation

TL;DR

This paper reviews the many-body theory of photoemission in solids, focusing on response theory, diagram classification, and new results on energy losses, proposing a regrouping method for spectral intensities to ensure positivity.

Contribution

It introduces a diagram regrouping approach that guarantees positive spectral intensities and extends the theoretical understanding of energy losses in valence-electron photoemission.

Findings

New results on energy losses in valence-electron photoemission from metal surfaces

A diagram grouping method that ensures spectral intensity positivity

Insights into response theory and diagram classification in photoemission

Abstract

The many-body theory of photoemission in solids is reviewed with emphasis on methods based on response theory. The classification of diagrams into loss and no-loss diagrams is discussed and related to Keldysh path-ordering book-keeping. Some new results on energy losses in valence-electron photoemission from free-electron-like metal surfaces are presented. A way to group diagrams is presented in which spectral intensities acquire a Golden-Rule-like form which guarantees positiveness. This way of regrouping should be useful also in other problems involving spectral intensities, such as the problem of improving the one-electron spectral function away from the quasiparticle peak.