High energy photoelectron spectroscopy of correlated electron systems and recoil effects in photoelectron emission

The bulk sensitivity of the high energy photoelectron spectroscopy (PES) in the soft and hard X-ray regions is gradually recognized to be essential for studying the electronic structures of strongly correlated electron systems with different surface and bulk electronic structures. With increasing h., the kinetic energy (EK) of photoelectrons is increased with realizing longer inelastic mean free path. Studies of three-dimensional genuine bulk band dispersions and bulk Fermiology are only possible by the soft X-ray angle resolved PES (ARPES). Examples are given for Nd2-xCexCuO4 and CeRu2X2(X: Si, Ge). The temperature dependence of the Yb 4f spectra provides useful information on valence fluctuation and Kondo resonance. The applicability of the single impurity Anderson model (SIAM) and its limit is discussed in the examples of Yb1-xLuxAl3 and YbAl3. The importance of the bulk sensitivity is also demonstrated by the soft and hard X-ray PES for SmOs4Sb12. When EK becomes very large, the nucleus (ion) recoil effects become observable on the core photoelectron emission from light elements. The example is shown for Yb7/8Lu1/8B12 and the influence of the recoil effects for the future high energy ARPES is briefly discussed.