Sum rules for X-ray magnetic circular dichroism spectra in strongly correlated ferromagnets

TL;DR

This paper proves the formal correctness of XMCD sum rules for strongly correlated ferromagnets, highlighting practical challenges in their application due to spectral broadening and the role of incoherent spectral density.

Contribution

It demonstrates the validity of XMCD sum rules in strongly correlated systems and discusses the impact of spectral density spreading on their practical use.

Findings

Sum rules are formally correct regardless of electron-electron interaction strength.

Spectral density spreading complicates the practical application of sum rules.

Incoherent spectral density plays a significant role in XMCD sum rules for strongly correlated systems.

Abstract

It is proven that the sum rules for X-ray magnetic dichroism (XMCD) spectra that are used to separate spin and orbital contributions to the magnetic moment are formally correct for an arbitrary strength of electron-electron interactions. However, their practical application for strongly correlated systems can become complicated due to the spectral density weight spreading over a broad energy interval. Relevance of incoherent spectral density for the XMCD sum rules is illustrated by a simple model of a ferromagnet with orbital degrees of freedom.