Electron-electron interaction strength in ferromagnetic nickel determined by spin-polarized positron annihilation

TL;DR

This study uses spin-polarized positron annihilation to measure and analyze electron-electron interactions in ferromagnetic nickel, providing a precise value for the local interaction strength U.

Contribution

It introduces a combined experimental and theoretical approach to accurately determine the electron-electron interaction strength in ferromagnetic nickel.

Findings

Electron-electron interaction strength U in Ni is 2.0 +- 0.1 eV.

Self-energy effects cause anisotropic contributions to momentum distribution.

Comparison with LDA+DMFT highlights the importance of many-body correlations.

Abstract

The two-photon momentum distribution of annihilating electron-positron pairs in ferromagnetic nickel (Ni) was determined by measuring the spin-polarized two-dimensional angular correlation of annihilation radiation (ACAR). The spectra were compared with theoretical results obtained within LDA+DMFT, a combination of the local density approximation (LDA) and the many-body dynamical mean-field theory (DMFT). The self-energy describing the electronic correlations in Ni is found to make important anisotropic contributions to the momentum distribution which are not present in LDA. Based on a detailed comparison of the theoretical and experimental results the strength of the local electronic interaction U in ferromagnetic Ni is determined as 2.0 +- 0.1 eV.