# Resonant x-ray spectroscopy of uranium intermetallics at the U $M_{4,5}$ edges

## TL;DR

This study uses resonant x-ray emission spectroscopy to analyze the electronic configurations of uranium intermetallics, revealing a predominant 5f^2 state in several compounds and demonstrating the technique's sensitivity to surface oxidation.

## Contribution

It provides detailed spectroscopic data on uranium intermetallics at the U M_{4,5} edges and compares their electronic states, highlighting the technique's effectiveness and surface sensitivity.

## Key findings

- UPd3 and URu2Si2 likely have 5f^2 configurations
- Surface oxidation affects USb sample analysis
- Spectra match well with theoretical calculations

## Abstract

We present resonant x-ray emission spectroscopic (RXES) data from the uranium intermetallics UPd$_3$, USb, USn$_3$ and URu$_2$Si$_2$, at the U $M_{4,5}$ edges and compare the data to those from the well-localized $5f^2$ semiconductor UO$_2$. The technique is especially sensitive to any oxidation of the surface, and this was found on the USb sample, thus preventing a good comparison with a material known to be $5f^3$. We have found a small energy shift between UO$_2$ and UPd$_3$, both known to have localized $5f^2$ configurations, which we ascribe to the effect of conduction electrons in UPd$_3$. The spectra from UPd$_3$ and URu$_2$Si$_2$,are similar, strongly suggesting a predominant $5f^2$ configuration for URu$_2$Si$_2$. The valence-band resonant inelastic x-ray scattering (RIXS) provides information on the U $P_3$ transitions (at about $18$~eV) between the U $5f$ and U $6p$ states, as well as transitions of between $3$ and $7$~eV from the valence band into the unoccupied $5f$ states. These transitions are primarily involving mixed ligand states (O $2p$ or Pd, Ru $4d$) and U $5f$ states. Calculations are able to reproduce both these low-energy transitions reasonably well.