# Manifestation of electron correlation effect in $\mathrm{U}~5f$ states of uranium compounds revealed by $\mathrm{U}~4d-5f$ resonant photoemission spectroscopy

## TL;DR

This study uses resonant photoemission spectroscopy to reveal how electron correlation effects influence the uranium 5f electronic states across different uranium compounds, highlighting the role of localization and Hubbard-U mechanisms.

## Contribution

It provides direct experimental imaging of uranium 5f density of states, demonstrating correlation effects and the Mott transition in actinide materials for the first time.

## Key findings

- Coherent peak at Fermi level matches band-structure calculations.
- Incoherent peak appears at higher binding energy in localized and heavy fermion compounds.
- Incoherent peak intensity increases and shifts with localization.

## Abstract

We have elucidated the nature of the electron correlation effect in uranium compounds by imaging the partial $\mathrm{U}~5f$ density of states (pDOS) of typical itinerant, localized, and heavy fermion uranium compounds by using the $\mathrm{U}~4d-5f$ resonant photoemission spectroscopy. Obtained $\mathrm{U}~5f$ pDOS exhibit a systematic trend depending on the physical properties of compounds. The coherent peak at the Fermi level can be described by the band-structure calculation, but an incoherent peak emerges on the higher binding energy side ($\lesssim 1~\mathrm{eV}$) in the \Uf pDOS of localized and heavy fermion compounds. As the $\mathrm{U}~5f$ state is more localized, the intensity of the incoherent peak is enhanced and its energy position is shifted to higher binding energy. These behaviors are consistent with the prediction of the Mott metal-insulator transition, suggesting that the Hubbard-$U$ type mechanism takes an essential role in the $5f$ electronic structure of actinide materials.