High-energy photoemission final states beyond the free-electron approximation

Three-dimensional (3D) electronic band structure is fundamental for understanding a vast diversity of physical phenomena in solid-state systems, including topological phases, interlayer interactions in van der Waals materials, dimensionality-driven phase transitions, etc. Interpretation of ARPES data in terms of 3D electron dispersions is commonly based on the free-electron approximation for the photoemission final states. Our soft-X-ray ARPES data on Ag metal reveals, however, that even at high excitation energies the final states can be a way more complex, incorporating several Bloch waves with different out-of-plane momenta. Such multiband final states manifest themselves as a complex structure and added broadening of the spectral peaks from 3D electron states. We analyse the origins of this phenomenon, and trace it to other materials such as Si and GaN. Our findings are essential for accurate determination of the 3D band structure over a wide range of materials and excitation energies in the ARPES experiment. Angular-resolved photoemission data is commonly used to determine the 3D electronic structure assuming free-electron final states. Strocov et al. show that even at high excitation energies the complexity of final states in various materials can go far beyond the free-electron picture.

Automated summary

A three-dimensional electronic band structure is crucial for understanding various physical phenomena in solid-state systems. Researchers have discovered that even at high excitation energies, the final states in materials like silver can be more complex than initially thought, incorporating multiple Bloch waves with different momenta. This complexity leads to broadening of spectral peaks and a complex structure in the photoemission data. These findings are important for accurately determining the 3D band structure in a wide range of materials and excitation energies in angular-resolved photoemission experiments.