AVS 49th International Symposium
    Surface Science Thursday Sessions
       Session SS-ThM

Paper SS-ThM7
Dominance of the Final State in Photoemission Mapping of the Fermi Surface of Co Thin Films

Thursday, November 7, 2002, 10:20 am, Room C-108

Session: Electronic Structure and Stimulated Processes
Presenter: R.L. Kurtz, Louisiana State University
Authors: R.L. Kurtz, Louisiana State University
X. Gao, Louisiana State University
A.N. Koveshnikov, Simon Fraser University, Canada
R.L. Stockbauer, Louisiana State University
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The Fermi surface of tetragonally-distorted fcc Co grown on Cu(001) has been investigated with angle-resolved photoemission and compared with first-principles calculations. Photoelectron angular distributions were obtained with a display-type ellipsoidal-mirror analyzer at the LSU CAMD synchrotron light source for electrons emitted from E@sub F@ using photons in the energy range of 20-80 eV. These angular distributions show distinct patterns that vary with photon energy as different regions of the Brillouin zone are sampled. In order to evaluate the correspondence to Fermi surface contours, we have computed the band structure of tetragonally-distorted Co. We have used WIEN97.9 to perform a spin-polarized gga FLAPW calculation including spin-orbit interactions for a pseudomorphic fcc structure with an in-plane lattice constant that of Cu while the vertical lattice parameter is reduced by 5%. From this, the resulting Fermi surfaces have been extracted and cross-sectional contours were produced corresponding to the various photon energies used in the measurements. We find that there is rather poor agreement between these contours and the structures seen in photoemission. To investigate this further, we have computed the momentum matrix elements using the final states produced in the band calculation. In the case of Co, the resulting angular distributions that we predict are in much better agreement with our data, and even reproduce the photon polarization effects that are observed. These observations suggest that comparison with first principles calculations are extremely important, particularly in the case of flat-band materials such as the d-bands of Co seen here. The slow dispersion of the occupied states, when coupled with the rapid dispersion of the final state, produces angular distributions whose contours are heavily influenced by the final state.