SHN Shi k (&pt) SPring-8  FEL x x PLD 1 X 2 3 ( 1 ) X ,   Chai nani , , (3) x & * 1,   Chai nani ) SPri ng- 8 (*1 RT X 2 (R = ; T= Fe, R1, Q; X= P, As, Sb) c-f 4f f Ce 3d 4f Ce 4f o f (4) Sril Q x , , , Chai nani , SrTi Q （STQ STO (I Œ TI 3d I Œ O ls O 2p I Œ Hal dane- Anderson I GS V 2p  V 1s I CS V Ti X x HPG C 1s HPG Ce 3d CeFe 4 P 12 f² 3 CeFe Sb12 CeOs Sb12 f² f Ce x ( 2 X , Chai nani g ) 340 K VQ (
High
(1)
resolution
hard
x-ray
photoelectron
spectroscopy
High resolution Hard X-ray Photoelectron Spectroscopy (HX-PES) is the method developed at SPring-8 using high brilliance synchrotron radiation, and is now becoming very useful tool in many synchrotron radiation facilities in the world. This year, we have studied the electronic structure of high-Tc cuprates, thin films of strongly correlated materials, f-electron etc. As an remarkable result, we succeed to observed recoil effect of photoelectron for the first time. C 1s photoelectrons of Highly Oriented Pyrolytic Graphite (HOPG) loose their kinetic energy, and the energy distribution becomes broader due to the recoil effect. The observed results are quantified by Prof. Kayanuma (Osaka Pref. Univ.). The physics of recoil effect of photoelectron is essentially the same as that of Mössbauer effect for γ –ray emission from nuclei, and the photoelectron spectra give us the information on phonon dynamics.
(2) Hard x-ray and soft x-ray photoemission study in VO 2
VO 2 , a d 1 electron system, exhibits a sharp first-order metal-insulator transition (MIT) as a function of temperature, at T MI = 340 K. VO 2 has attracted enormous attention in terms of a Mott-Hubbard correlation-induced versus a structural Peierls-type MIT. We performed bulk sensitive hard x-ray and soft x-ray photoemission spectroscopy to investigate the electronic structure of VO 2 . Across the MIT, spectral weight transfer from V 3d character coherent states at Fermi level to the incoherent band leads to gap-formation. Coupled changes in V 2p and V 1s core levels, with well-screened features only in the metallic phase, are nicely reproduced by a cluster model.
(3) Soft x-ray photoemission spectroscopy for Ce-filled
skutterudites The filled skutterudite compounds with a general formula RT 2 X 12 (R = rare earth; T = Fe, Ru and Os; X = P, As and Sb) have attracted much attention since they exhibit a variety of strongly correlated electron phenomena. Among these compounds, CeFe 4 P 12 is a semiconductor with an energy gap of ~130 meV. On the other hand, CeFe 4 Sb 12 and CeOs 4 Sb 12 show anomalous temperature-dependent transport behavior. These properties may be related with the hybridization between conduction ( c ) and Ce 4 f states. In order to clarify the relation between their physical properties and c-f hybridization, we have investigated the electronic structure of CeFe 4 P 12 and CeOs 4 Sb 12 by soft X-ray photoemission spectroscopy (PES). For Ce 3d core level PES spectra of CeFe 4 P 12 , three peak structures due to f 0 , f 1 and f 2 final states were clearly observed. On the other hand, no clear f 0 and f 2 structures were observed for CeFe 4 Sb 12 and CeOs 4 Sb 12 . In addition, the detailed valence-band structures of Ce-filled skutterudites were investigated by Ce 3d-4f resonant PES. The difference of their spectral properties can be explained by the degree of c-f hybridization. (4) Soft X-ray resonant photoemission spectroscopy of electron-doped SrTiO 3 SrTiO 3 crystal is one of the promising device materials for "oxide electronics", since it exhibits novel phenomena as interfacial metalicity such and   state-of-the-art thermoelectric performance. The electronic excitation spectra of electron-doped SrTiO 3 shows an incoherent excitation (ICE) appearing in the band gap of the host SrTiO 3 . In order to elucidate the origin of the ICE, we performed resonant photoemission spectroscopy at the O 1s and Ti 2p absorption edges on a Nb-doped SrTiO 3 epitaxial thin film. We find that the ICE has mixed character of O 2p and Ti 3d states, contrasted to the earlier notion that the ICE is mainly composed of Ti 3d states. The ICE could be considered qualitatively equivalent to the multiple charge states of a transition metal in a semiconductor as proposed by Haldane and Anderson. Staff Head Dr. Shik SHIN Members Dr. Ashish CHAINANI Dr. Ritsuko EGUCHI Dr. Yoshihisa HARADA Dr. Koji HORIBA Dr. Yoshiharu MIYAJIMA Dr. Masaki OURA Dr. Munetaka TAGUCHI Dr. Yasutaka TAKATA Dr. Tomoyuki TAKEUCHI Dr. Tadashi TOGASHI Dr. Takashi TOKUSHIMA Dr.Yukiaki ISHIDA Special Postdoctoral Researcher Visiting Members Prof. Emst E KURMAEV (Russian Aca. Sic.) Prof. Takayoshi YOKOYA (Grad. Sch Sci & Tech, Okayama Univ.) Dr. Kyoko ISHIZAKA (ISSP) Dr. Takahiro ITO (Inst. Molecular Sci.) Dr. Nozomu KAMAKURA(KEK/PF) Dr. Eiichi KOBAYASHI (AIST) Dr. Hiroshi KUMIGASHIRA (Fac Eng. Tokyo Univ.) Dr. Yuji MURAOKA (Grad. Sch Sci & Tech, Okayama Univ.) Dr. Tomohiko SAITO (Fac Sci. Tokyo Sci Univ.) Dr. Shunsuke TSUDA (ISSP) Dr. Takanori WAKITA (Fac. Sci., Okayama Univ.) Dr. Ichizo YAGI (AIST) Trainees Mr. Kouhei FUJIWARA (ISSP) Mr. Yusuke HITAKA (Grad. Eng. Univ. Hyogo) Mr. Mario OKAWA (ISSP) Mr. Hiroyuki OKAZAKI (Grad. Sci., Okayama Univ.) Mr. Kuninari SAEKI (Fac. Sci., Okayama Univ.) Mr. Shouhei WADA (Grad. Sci., Okayama Univ.) Mr. Kenichi YAKIGAYA (ISSP)