Fingerprints of entangled spin and orbital physics in itinerant ferromagnets via angle-resolved resonant photoemission

Abstract

A novel method for mapping the local spin and orbital nature of the ground state of a system via corresponding flip excitations in both sectors is proposed based on angle resolved resonant photoemission and related diffraction patterns, presented here for the first time via an ab-initio modified one-step theory of photoemission. The analysis is done on the paradigmatic weak itinerant ferromagnet bcc Fe, whose magnetism, seen as a correlation phenomenon given by the coexistence of localized moments and itinerant electrons, and the non-Fermi liquid behaviour at ambient and extreme conditions both remain unclear. The results offer a real space imaging of local pure spin flip and entangled spin flip-orbital flip excitations (even at energies where spin flip transitions are hidden in quasiparticle peaks) and of chiral, vortex-like wavefronts of excited electrons, depending on the orbital character of the bands and the direction of the local magnetic moment. Such effects, mediated by the hole polarization, make resonant photoemission a promising tool to perform a full tomography of the local magnetic properties of a system with a high sensitivity to localization/correlation, even in itinerant or macroscopically non magnetic systems.

Unexpectedly large electron correlation measured in Auger spectra of ferromagnetic iron thin films: orbital-selected Coulomb and exchange contributions

“…The data analysis reported in the following, builds on the Fe DOS calculated in DFT-LSDA by Rhee [54] for a 3 ML Fe ultrathin film on Ag(100) and for bulk Fe, the latter being in very good agreement with a recent (DFT-LSDA) calculation [4]. The 2 ML-thick film here investigated has been modelled using Rhee's DOS of the surface (top) and interface (bottom) layers; this latter weighted by the effective mean free path of the emitted electron pair [55].…”

“…The extraordinary macroscopic properties of technologically relevant materials exploiting quantum effects, including magnetism itself, are mainly determined by the relevance of electron-electron correlations. The development of novel magnetic and spintronic devices, nowadays evolving more and more at the nanoscale and at the interface level, requires an accurate comprehension of the strongly correlated nature of d or f electron shells, in terms of local and non-local Coulomb and exchange interactions, which depend on energy, orbital, momentum and spin degrees of freedom [1][2][3][4]. Density functional theory (DFT) [5] and computational methods referred as "Beyond-DFT" [6] provide accurate descriptions of the ground state of moderately-correlated materials while strongly-correlated materials and their excited states still pose significant challenges [7].…”

One-step approach to ARPES from strongly correlated solids: A Mott-Hubbard system

“…The atomic units = e = m e = 1 are used. In resonant photoemission [47][48][49][50] or in the presence of microscopic fields due to the dielectric screening 51,52 the operator Ô is more involved, which complicates the calculation of matrix elements M k , E in Eq. ( 20), but the theory presented below remains fully applicable Following Ref.…”