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Angle-resolved photoemission is widely used to study electronic
structure of solids. However, to extract the information from the
experiment is not straightforward. It is only now, 30 years after
the first ab initio theory of photoemission has been developed,
that we realize how complex the relation between the measured
spectra and the underlying band structure is.
In this talk an ab initio theory of photoemission is presented based on the Bloch waves approach to electron scattering within the augmented plane waves formalism. Theoretical grounds are established for so-called band mapping: deriving the quasi-particle band structure of a crystal from a surface sensitive photoemission experiment. The high selectivity of the process of electron excitation and escape makes the problem non-trivial. Interference between Bloch constituents of the photoelectron initial and final states in the presence of inelastic scattering is discussed and its implications for band mapping and for determining the lifetimes of initial and final states. Valence band photoemission from aluminum -- a textbook example of a `nearly-free-electron metal' -- is considered and from layered crystals VSe2 and TiTe2. The study of the photoemission from surface states on (100) and (111) surfaces of Al and Cu covers the final state kinetic energy range up to 100 eV and reveals strong multiple-scattering (band structure) effects at high energies. The elastic scattering origin of the emission windows and the role of complex band structure in formation of the spectra is discussed. |
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