Final state effects in photoemission studies of Fermi surfaces

Abstract

Photoelectron spectroscopy is one of the most important methods for extracting information about the Fermi surface (FS) of materials. An electron photoexcited from the FS is emitted from the crystal conserving the parallel momentum, k , while the perpendicular momentum k ⊥ is reduced due to the surface potential barrier. A simple interpretation of the process assumes the final state is freeelectron-like allowing one to 'map' the detected photoelectron back to its initial k momentum. There are multiple final state effects that can complicate the interpretation of photoelectron data and these effects are reviewed here. These can involve both energy and k broadening, which can give rise to shadow or ghost FS contours, scattering and final state diffraction effects that modify intensities, and matrix element effects which reflect the symmetries of the states involved and can be highly dependent on photon polarization. These matrix elements result in contours of photoelectron intensity that follow the dispersion in k-space of the initial state, the FS, and the final state. Locations where intensities go to zero due to matrix element and symmetry effects can result in gaps where FS contours 'disappear'. Recognition that these effects can play a significant role in determining the measured angular distributions is crucial in developing an informed model of where the FS contours actually lie in relation to measured intensity contours.

Fermi surface and effective masses in photoemission response of the (Ba1−x K x )Fe2As2 superconductor

“…the BaFe 2 As 2 parent compound and connected with the k z dispersion of the valence states 11 . The apparent mass enhancement is given by the fact that the ARPES response of the 3D valence states is formed by averaging of their matrix-element weighted k z dispersion over an interval of the intrinsic final state k z broadening (Δ k z ) determined by the photoelectron mean free path λ 43 , 44 .…”

Coverage-dependent adsorption geometry of octithiophene on Au(111)

“…A further increase of the photoemission intensity from the HOMO-1 for coverages above 1 ML may be attributed to a higher number of molecules present on the surface. Note that also final state effects influence the photoemission intensities 35 .…”

Quantitative Ultrafast Electron‐Temperature Dynamics in Photo‐Excited Au Nanoparticles

“…The two NP spectra (blue and green markers in Figure 2) were measured at the same sample temperature, yet exhibit a slight smearing of the Fermi edge accompanied by a small spectral shift to higher binding energies with respect to the reference bulk Au. Both phenomena are due to well-known finite-state effects in photoemission, typical of spatiallyconfined systems, [46,47] and can be effectively represented by a slight decrease of the energy resolution, and allowing for a small shift of E F in the fitting function. The best fits of the Au-NP spectra were then performed holding ϑ e at 137 K while allowing ℓ(E), E F and the experimental resolution to vary.…”