Ab initio many-body photoemission theory of transverse energy distribution of photoelectrons: PbTe(111) as a case study with experimental comparisons

TL;DR

This paper introduces the first fully ab initio many-body photoemission theory to accurately predict transverse energy distributions of photoelectrons from single-crystal photocathodes, validated by experiments on PbTe(111).

Contribution

It develops a novel ab initio framework that accounts for many-body effects, improving predictions of photoemission properties over previous density-functional theory approaches.

Findings

The theory accurately reproduces measured MTEs of PbTe(111).

It explains photoemission below the predicted threshold.

Many-body effects are crucial for understanding photoemission from PbTe(111).

Abstract

This manuscript presents, to our knowledge, the first fully ab initio many-body photoemission framework to predict the transverse momentum distributions and the mean transverse energies (MTEs) of photoelectrons from single-crystal photocathodes. The need to develop such a theory stems from the lack of studies that provide complete understanding of the underlying fundamental processes governing the transverse momentum distribution of photoelectrons emitted from single crystals. For example, initial predictions based on density-functional theory calculations of effective electron masses suggested that the (111) surface of PbTe would produce very small MTEs ($\leq$ 15 meV), whereas our experiments yielded MTEs ten to twenty times larger than these predictions, and also exhibited a lower photoemission threshold than predicted. The ab initio framework presented in this manuscript correctly reproduces the magnitude of the MTEs from our measurements in PbTe(111) and also the observed photoemission below the predicted threshold. Our results show that photoexcitations into bulk-like states and coherent, many-body electron-photon-phonon scattering processes, both of which initial predictions ignored, indeed play important roles in photoemission from PbTe(111). Finally, from the lessons learned, we recommend a procedure for rapid computational screening of potential single-crystal photocathodes for applications in next-generation ultrafast electron diffraction and X-ray free-electron lasers, which will enable new, significant advances in condensed matter research.