title: Soft x-ray spectroscopy of Ba24Ge100: electronic phase transition and Ba-atom rattling.
abstract: The electronic states of Ba24Ge100 are studied by soft x-ray photoelectron spectroscopy (XPS) at a high-energy photon factory. A large reduction in the density of states (DOS) at the Fermi level is clearly shown before and after the electronic phase transition at 200 K. The changes in the spectrum widths and the fine structures of the core-level Ba 4d spectra give a very reasonable indication of the Ba-atom rattlings in the clathrate polyhedra. On-resonance experiments using the excitation from Ba 3d to 4f levels display that the wave functions of Ba 5d and 6s orbitals give only a small contribution to make a Fermi surface through the hybridization with the Ge20 cluster orbitals. Importantly, reliable values of the DOS at the Fermi level NEF are successfully deduced, using two data sets of DOS obtained from high-resolution XPS and the total magnetic susceptibilities by a superconducting quantum interference device, to be 0.149 and 0.0427 states eV(-1) (Ge atom)(-1) for a high-temperature and for a low-temperature phase.
authors.affiliation: Department of Physics, Graduate School of Science, Tohoku University and Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), Miyagi 980-8578, Japan. rachi@sspns.phys.tohoku.ac.jp
authors.forename: Takeshi
authors.initials: T
authors.lastname: Rachi
authors.forename: Masaki
authors.initials: M
authors.lastname: Kitajima
authors.forename: Kensuke
authors.initials: K
authors.lastname: Kobayashi
authors.forename: FangZhun
authors.initials: F
authors.lastname: Guo
authors.forename: Takehito
authors.initials: T
authors.lastname: Nakano
authors.forename: Yuka
authors.initials: Y
authors.lastname: Ikemoto
authors.forename: Keisuke
authors.initials: K
authors.lastname: Kobayashi
authors.forename: Katsumi
authors.initials: K
authors.lastname: Tanigaki