Disentangling Electron-Boson Interactions on the Surface of a Familiar Ferromagnet

We report energy renormalizations from electron-phonon and electron-magnon interactions in spin minority surface resonances on Ni(111). The different interactions are identified, disentangled, and quantified from the characteristic signatures they provide to the complex self-energy and the largely different binding energies at which they occur. The observed electron-magnon interactions exhibit a strong dependence on momentum and energy band position in the bulk Brillouin zone. In contrast, electron-phonon interactions from the same bands appear to be relatively momentum- and symmetry-independent. Additionally, a moderately strong ($\lambda>0.5$) electron-phonon interaction is distinguished from a near-parabolic spin majority band not crossing the Fermi level.