High-resolution soft X-ray bulk sensitive photoemission from strongly correlated systems

In order to probe bulk electronic states of correlated electron systems nea r the Fermi level, high resolution photoemission spectroscopy by excitation in the soft X-ray region above several hundred eV is a very powerful tool. The best combination of the light source, analyzer, samples and miscellane ous experimental conditions is required. Photon resolution down to 50 meV a nd photoelectron total energy resolution down to 80 meV is realized near 1 keV as a breakthrough of bulk sensitive high resolution photoemission spect roscopy (BHPES), in which surface 4f electronic states are found to be sign ificantly depressed. The BHPES spectra are very much different from the res ult of surface sensitive spectra measured slightly above 100 eV or by use o f He II and I. Some BHPES results are demonstrated for Yb and Ce Kondo and valence fluctuating compounds. (C) 2001 Elsevier Science B.V. All rights re served.