We are currently using the WIEN2k LAPW code to calculate electronic band structures using the generalized gradient approximation. This allows us to predict the initial state Fermi Surface coutours that we probe in photoemission. We find that the visualization of these complex 3D beasts is not a trivial matter as in the d-band FS of Ni. We are also using this to help us predict angle-resolved dichroism and the strong polarization dependences that exist in photoemission.

Our recent work measuring the angular distributions of photoelectrons came up with a surprising result. When we compared the angular distribution patterns determined with an ellipsoidal-mirror analyzer with the structure of the initial-state Fermi surface, we found what seemed to be very little correspondence.

By using DFT to calculate BOTH the initial and final states in photoemission from the Fermi surface of fcc Co/Cu(001) we found that the FINAL STATE determined the pattern of the photoelectrons that was observed.

• Calculated electronic structure and Fermi surface of fcc Co.
• Comparison of experimental and theoretically predicted photoelectron angular distributions

This has significant implications in any angle-resolved photoemission determination of Fermi surface structure: The data you may try to interpret as an initial state such as the Fermi surface, may actually better reflect the final state in the excitation. This effect is expected to be VERY important in interpreting data from high-T_c superconductors and flat-band systems such as heavy fermion materials.

In our studies of Ni films on Cu(001) we found unexpected bulk Fermi surfaces for monolayer films. We had expected to see 2D Fermi surfaces that eventually evolved to 3D in thick films. In order to compare with our angular distributions, we have calculated the band structure of Ni using the gga approach to the lsda. From that calculation, we compute the FS contours and render the data in 3D using IDL.

For a better understanding of the odd shape of this beast, take it for a spin with this Quicktime mov (645Kb) that allows you to view it from various angles. We have another which is a Quicktime object (1.2 MB) which you can spin with your mouse.

The band structure was calculated using WIEN97. We then calculated the eigenvalues on a very tight mesh in the Brillouin zone. This data was imported into IDL (Research Systems, Inc.) and the isosurface at E=0 eV was rendered. For the 3D object, this was done for views from the various angles. The object was then assembled using QuickTime VR Authoring Studio. The final "trick" that lets it survive the unix web server is to open the mov with Apple's Quicktime Player 4.01 and save a copy of the mov using the option "make movie self-contained." This copy is the file that survives the unix server and downloads in a playable manner.