Theory of temperature-dependent photoemission in 3d-band ferromagnets: Application to Ni(110) and Ni(111)

The effects of electron correlations and phonons on the temperature dependence of ultraviolet photoemission and bremsstrahlung isochromat spectra of ferromagnetic Ni are investigated. The spin- and and temperature-dependent photocurrent is calculated in the framework of a generalized one-step model of photoemission. Phonons are taken into account via temperature-dependent phase shifts. The hole state of photoemission is described by an energy-, spin-, and temperature-dependent self-energy, which rests on a combination of density-functional theory and a Hubbard-type multiband model. The comparison of calculated spin-polarized and temperature-dependent spectra for Ni(110) and Ni(111) with experimental data shows excellent agreement, in particular for the Ni(110) surface. No indication of a stationary exchange splitting independent of temperature could be found. Instead the merging of the majority and minority spin states upon approaching the Curie temperature ${\mathit{T}}_{\mathit{C}}$ was indentified unambiguously in essentially all relevant cases.