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

Abstract

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 hν, the kinetic energy (E K ) 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 Nd 2 - x Ce x CuO 4 and CeRu 2 X 2 (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 Yb 1 - x Lu x Al 3 and YbAl 3 . The importance of the bulk sensitivity is also demonstrated by the soft and hard X-ray PES for SmOs 4 Sb 12 . When E K becomes very large, the nucleus (ion) recoil effects become observable on the core photoelectron emission from light elements. The example is shown for Yb 7/8 Lu 1/8 B 12 and the influence of the recoil effects for the future high energy ARPES is briefly discussed.