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

Abstract

We employ a positron annihilation technique, the spin-polarized two-dimensional angular correlation of annihilation radiation (2D-ACAR), to measure the spin-difference spectra of ferromagnetic nickel. The experimental data are compared with the theoretical results obtained within a combination of the local spin density approximation (LSDA) and the many-body dynamical mean-field theory (DMFT). We find that the self-energy defining the electronic correlations in Ni leads to anisotropic contributions to the momentum distribution. By direct comparison of the theoretical and experimental results we determine the strength of the local electronic interaction U in ferromagnetic Ni as 2.0 ± 0.1 eV.

Electronic correlations in vanadium revealed by electron-positron annihilation measurements

“…The 2D-ACAR technique is a powerful tool to investigate the bulk electronic structure 12,[30][31][32][33][34] . It is based on the annihilation of positrons with electrons in the sample, leading to the emission of two γ-quanta in nearly antiparallel directions.…”

“…This made it possible, for example, to experimentally pinpoint the strength of the local electronic interaction in Ni. 12 Vanadium is a 3d transition metal element with the electronic configuration of [Ar] 3d 3 4s 2 . The electronic structure of vanadium has been intensively studied by electron-positron annihilation [13][14][15][16][17][18][19][20][21][22][23][24] and, less so, by the de Haas -van Alphen (dHvA) effect 25,26 and photoemission 27,28 .…”

Spin-Resolved Fermi Surface of the Localized Ferromagnetic Heusler CompoundCu2MnAlMeasured with Spin-Polarized Positron Annihilation

“…The mean emission energy of 22 Na yields a maximum P ¼ 0.835, although in practice it is reduced by backscattering inside the source and by geometrical factors. In our experimental configuration it has been measured to be P ¼ 0.673 [19].…”

“…Spin-polarized 2D-ACAR has been used to prove half-metallicity in NiMnSb [17,18] and to determine the electron-electron interaction strength in Ni [19]. Compared to angle-resolved photoemission spectroscopy (ARPES) the (high energy) positron probing the bulk is not affected by the surface, and the photon-matter interaction (which can complicate the analysis of ARPES data) does not have to be considered.…”

“…If both M p and M a are measured, straightforward algebra shows that it is possible to isolate the majority and minority spectra. Further insight into spin-polarized 2D-ACAR measurements can be found elsewhere [18,19,23].…”