Inverse combined with direct photoemission : momentum resolved electronic structure of 2D systems

Abstract From angle resolved inverse and direct photoemission spectroscopy in different detection modes one can derive the momentum resolved electronic structure of unoccupied and occupied states of solids and their surfaces. The power of the methods will be demonstrated by comparing recent experimental results of two-dimensional systems like layered materials, high temperature superconductors and semiconductor surfaces with calculations concerning volume and surface bands including quasi particle aspects of the interacting electron system. The in situ combination of both methods is particularly suited to investigate the close vicinity of the Fermi level for both, unoccupied and occupied states, which provides significant information on properties of Fermi surfaces, appearance of gaps in phase transitions for metallic systems and surface electronic gaps of semiconductors.