Resolving unoccupied electronic states with laser ARPES in bismuth-based cuprate superconductors

TL;DR

This paper demonstrates the use of laser ARPES to observe unoccupied electronic states in bismuth-based cuprate superconductors, revealing features related to final-state gaps and expanding ARPES capabilities.

Contribution

It introduces a method to probe unoccupied states with laser ARPES, previously limited to occupied states, by identifying features linked to final-state gaps.

Findings

Observed dispersive suppression related to unoccupied states

Linked features to final-state gaps 6 eV above Fermi level

Showed conditions to minimize final-state effects

Abstract

Angle-resolved photoemission spectroscopy (ARPES) is typically used to study only the occupied electronic band structure of a material. Here we use laser-based ARPES to observe a feature in bismuth-based superconductors that, in contrast, is related to the unoccupied states. Specifically, we observe a dispersive suppression of intensity cutting across the valence band, which, when compared with relativistic one-step calculations, can be traced to two final-state gaps in the bands 6 eV above the Fermi level. This finding opens up possibilities to bring the ultra-high momentum resolution of existing laser-ARPES instruments to the unoccupied electron states. For cases where the final-state gap is not the object of study, we find that its effects can be made to vanish under certain experimental conditions.