Recent Progress of Photoelectron Spectroscopy and Holography. Studies of Bulk and Surface Electronic States of Correlated Materials by High Energy Photoemission Spectroscopy.

Abstract

High resolution photoemission spectroscopy (HPES) has mostly been performed so far at energies below slightly higher than 100 eV. This is due to the necessity for the high enough resolution of photons. Nowadays high resolution better than a few me V is feasible by use of the state of art electron energy analyzers and very bright He I, II light sources. For angle resolved photoemission spectroscopy (ARPES), even angular resolution of better than ± 0.1 degree is feasible. Thus the low photon energy (hν) PES and ARPES are very popular in many laboratories. However, these measurements are relatively surface sensitive. In many cases of strongly correlated electron systems such as 4 f rare earth and 3 d transition metal systems, the surface electronic structures are much different from the bulk. Therefore bulk sensitive HPES is strongly required for bulk studies. The difference of the surface and bulk electronic states is reviewed by showing recent results of bulk sensitive soft X-ray HPES and ARPES measurements.