The interplay of local electron correlations and ultrafast spin dynamics in fcc Ni

TL;DR

This study combines femtosecond X-ray spectroscopy and ab initio theory to explore how local electron correlations influence ultrafast spin dynamics in fcc Ni, revealing a complex interplay of electronic interactions.

Contribution

It provides a detailed analysis of the temporal interplay between band formation, exchange interaction, and Coulomb repulsion in ferromagnetic nickel using combined experimental and theoretical methods.

Findings

Transient spectral broadening due to electron repopulation

Energy shifts caused by correlation-induced electronic modifications

Local Coulomb interactions are essential for accurate description

Abstract

The complex electronic structure of metallic ferromagnets is determined by a balance between exchange interaction, electron hopping leading to band formation, and local Coulomb repulsion. The interplay between the respective terms of the Hamiltonian is of fundamental interest, since it produces most, if not all, of the exotic phenomena observed in the solid state. By combining high energy and temporal resolution in femtosecond time-resolved X-ray absorption spectroscopy with ab initio time-dependent density functional theory we analyze the electronic structure in fcc Ni on the time scale of these interactions in a pump-probe experiment. We distinguish transient broadening and energy shifts in the absorption spectra, which we demonstrate to be caused by electron repopulation and correlation-induced modifications of the electronic structure, respectively. Importantly, the theoretical description of this experimental result hence requires to take the local Coulomb interaction into account, revealing a temporal interplay between band formation, exchange interaction, and Coulomb repulsion.