Recent development in soft X-ray spectroscopy of correlated materials: High resolution absorption and bulk-sensitive photoemission

An extremely high quality soft X-ray beam line was constructed at BL25SU of SPring-8. A varied line spacing plane grating monochromator (VLSPGM) equipped with gratings with the central groove density of 600 and 1,000/mm can cover the energy region from 0.22 to 2 keV by the use of the fundamental radiation from the twin helical undulator, The energy resolution of VLSPGM is beyond 20,000 at I keV. The total resolution of practical photoelectron spectroscopy (PES) of better than 80 meV is achieved at 880 eV. The PES measurements performed above several hundred eV have shown the bulk sensitivity in many materials and provided spectra much different from the surface-sensitive spectra so far obtained below slightly above 100 eV or by He II and I light sources. As a breakthrough, bulk-sensitive angle-resolved photoemission spectroscopy (ARPES) is demonstrated to be a very powerful means of studying the bulk electronic states of correlated electron systems.