Fig.1. Schematic view of the Photoemission (top) and Inverse Photoemission (bottom) processes. Fig.2. PES and IPES spectra of polycrystalline silver, plotted with a common Fermi level (at E=0). Together they probe the density of states (DOS).

Fig.3. Universal curve of the photoelectron elastic mean free path as a function of kinetic energy. Fig.4. An impossible vertical transition for a free electron (left), and transitions involving reciprocal lattice vectors in a periodic potential.

Fig.5. Escape conditions for a hot electron at the sample surface. Only the component of the electron momentum along the surface is conserved. The electron is refracted. Fig.6. An ARPES experiment on a metal.The energy of the ARPES peak changes with the emission angle (with parallel momentum), reproducing the dispersion of the underlying band.

Fig.7. ARPES spectra of the quasi-1D compound (NbSe 4 ) 3 I along the 1D direction. The band dispersion is well visible in the intensity map. Fig.8. ARPES intensity map of LaRu 2 Si 2 measured at E=E F, compared with a theoretical Fermi surface. From Ref. 6.

Fig.9. Artists view of an ARPES spectrum in the opposite sudden and adiabatic limits. The 0 transition corresponds to the ground state of the (N-1)-electron system. Fig.10. Artists view of the k-dependent ARPES spectral function is the free-electron limit (left) and in an interacting system (right). (adapted from M. Meinders; PhD Thesis, Groningen (1994)).

Fig.11. Theoretical (line) and experimental dispersion of the conduction band of sodium. The band narrowing is a typical consequence of electronic correlations. From Ref. 10. Fig.12. Cuts of the ARPES intensity map produce Energy distribution curves (EDCs, at constant k) or Momentum distribution curves (MDCs, at constant energy).

Fig.13. Normal emission spectra from quantum well states in epitaxial Ag(100) films of varying thickness. From Ref. 12. Fig.14. ARPES Fermi liquid lineshapes in the 2D metal TiTe 2. Notice the typical FL tail beyond k F. From Ref. 13.

Fig.15. QP spectra of TiTe 2 measured at the Fermi surface at various temperatures. The temperature-dependent linewidth reflects the increasing electron-phonon scattering at high T. (adapted from Ref. 14). Fig.16. Experimental and theoretical ARPES spectra of a surface state on Be(0001), showing the effect of a strong electron-phonon interaction. The renormalized dispersion is shown in b). From Ref. 15. b)

Fig.17. Expected dispersion and DOS(top) in a SC or CDW state, within a mean-field scenario. Fig.18. (left) Gap opening in the SC cuprate Bi (right) Evolution of the SC gap as a function of doping in Bi From Ref. 21.

Fig.19. Angular dependence of the SC gap in Bi extracted from ARPES data. The dependence is consistent with a d-wave scenario.From Ref. 22. Fig.20. PES spectra of V 3 Si above and below the SC transition. The lines are BCS fits. Notice the small hump above E F, from thermally populated states above the gap. (inset) T-dependence of (T). From Ref. 23.

Fig.21. Temperature-dependent raw (left) and symmetrized spectra of a C 60 monolayer on the Ag(100) surface, showing the opening of a gap at E F. From Ref. 25. Fig.22. Temperature-dependent spectra of a gold reference and of the Kondo insulator CeRhAs illustrate the opening of a pseudogap at E F in the latter. The spectra were divided by the Fermi distribution. From Ref. 24.

Fig.23. ARPES Fermi surface map of the 2D CDW material 2H-NbSe 2.The arrow shows a possible nesting vector. From Ref. 27. Fig.24. (left) ARPES intensity map of the 2D CDW system 2H-TaSe 2 along the K direction. (right) Spectra measured at the 2 FS crossings, above and below T P. A gap opens only at k F2. From Ref. 28.

Fig.25. Very high resolution spectra of 2H-NbSe 2, measured on two different FS sheets across the SC transition (T SC =7.2 K). From Ref. 29. Fig.26. ARPES intensity map of 1T-TaS 2 in the metallic (left) and insulating (center) phase. The opening of a Mott-Hubbard gap is also evident from the spectra (right). From Ref. 30.

Fig.27. (left) ARPES intensity map for the organic 1D compound TTF-TCNQ. (right) The spectrum at k=k F exhibits a deep pseudogap. From Ref. 31. Fig.28. Calculated spectral function of the Luttinger Liquid, showing separate spinon and holon excitations. From Ref. 33.

Fig.29. Experimental valence band dispersion in 1D SrCuO 2 and in a 2D cuprate (right). The broader 1D dispersion is compatible with spin-charge separation in 1D. From Ref. 35. Fig.30. RESPES spectra of the Kondo system CePd 3 measured across the Ce 4d absorption edge. (inset) Photon energy dependence of the 4f signal. From Ref. 36.

Fig.31. Decomposition into triplet and singlet components of the spectrum of the SC compound Bi Spin- resolved data were taken at the Cu 2p-3d resonance. From Ref. 38. Fig.32. RESPES spectra of the Kondo system CeRu 2 Si 2 measured at the Ce 3d and Ce 4d edges, with different surface sensitivity. From Ref. 39.

Fig.33. Spectra of the 3d core levels of metallic samarium, at 3 different photon energies. The Sm 2+ surface component is drastically reduced in the bulk- sensitive high energy spectrum. From Ref. 41. Fig.34. Band mapping at the Cu(100) surface with high energy photons (h. (courtesy of C. Dallera)