No abstract

The setup of an electron spectrometer for angle-resolved photoemission is described. A sample goniometer offers the opportunity for angle scanned photoemission over 2 solid angle above the surface. A monochromatized high flux He discharge photon source is exploited to measure thermally populated electronic states above the Fermi level E F. At energies greater than E F ϩ5k B T the signal from a constant density of states declines below the photoelectron background caused by photons with higher energies than He I␣ ͑21.2 eV͒. For He II␣ ͑40.8 eV͒ the residual photoelectron background is lower and photoemission up to 6k B T above E F can be performed. Data showing two cuts through the Fermi surface of silver are presented. Furthermore the dispersion of the Shockley surface state on Ag ͑111͒ above the Fermi energy is quantified.

The magnetic phase transition in nickel metal has been studied with high resolution photoemission spectroscopy. A monochromatized high intensity He Ia photon source provides access to the dispersion of thermally populated states up to 5k B T above the Fermi level. On Ni(111) the coalescence of the partially occupied minority d band and the occupied majority d band is observed in raising the temperature above the Curie point. Close to a fast dispersing sp band anomalously high intensity from the minority d band is found. This is a clue that sp-d fluctuations at the Fermi level are a driving force in the magnetic phase transition. [S0031-9007(97)04631-0]

No abstract

An extended set of temperature-dependent ARUPS data from Ni͑111͒ is presented. The ferromagnetic and the paramagnetic state as well as the phase transition are examined in great detail. Rather new and unconventional modes of data acquisition in ARUPS are applied with high angular and energy resolution, exhibiting great power near the Fermi energy E F . Even up to 5k B T above E F energy bands are readily observed. The understanding of these ARUPS data is strongly enhanced by spin-polarized band structure calculations. Exchange-split bands of both, sp-and d-character, are resolved in angular scans and in photoemission Fermisurface maps. From two-dimensional data sets in energy and angle the dispersion and the exchange splitting are obtained with high precision. All the observed sp-and d-bands clearly exhibit a Stoner-like collapsing-band behavior. The exchange splitting ⌬E ex vanishes above T C in all cases, and ⌬E ex closely follows the temperature dependence of the macroscopic magnetization. The apparent deviations from the Stoner-like band behavior stated in P. Aebi et al., Phys. Rev. Lett. 76, 1150 ͑1996͒ are explained. Furthermore we detect anomalously high intensity from a minority d-band close to an sp-band. This strongly suggests that sp-d-fluctuations at the Fermi level are a driving force for the magnetic phase transition of nickel.