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Search Results: 1 - 10 of 400786 matches for " M. Yabashi "
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X-ray Resonance in Crystal Cavities--Realization of Fabry-Perot Resonator for Hard X-rays
S. -L. Chang,Yu. P. Stetsko,M. -T. Tang,Y. -R. Lee,W. -H. Sun,M. Yabashi,T. Ishikawa
Physics , 2004, DOI: 10.1103/PhysRevLett.94.174801
Abstract: X-ray back diffraction from monolithic two silicon crystal plates of 25--150 um thick and a 40--150 um gap using synchrotron radiation of energy resolution deltaE=0.36 meV at 14.4388 keV shows clearly resonance fringes inside the energy gap and the total-reflection range for the (12 4 0) reflection. This cavity resonance results from the coherent interaction between the X-ray wavefields generated by the two plates with a gap smaller than the X-ray coherence length. This finding opens up new opportunities for high-resolution and phase-contrast X-ray studies, and may lead to new developments in X-ray optics.
Photoemission Evidence for Valence Fluctuations and Kondo Resonance in YbAl2
M. Matsunami,A. Chainani,M. Taguchi,R. Eguchi,Y. Takata,M. Oura,M. Yabashi,K. Tamasaku,Y. Nishino,T. Ishikawa,M. Kosaka,S. Shin
Physics , 2012, DOI: 10.1143/JPSJ.81.073702
Abstract: We use hard x-ray photoemission spectroscopy (HAXPES) to investigate the electronic structure of YbAl2, for which the Yb valence has not been consistently reported to date. The bulk sensitivity and the analytical simplicity provided by the Yb 3d core-level HAXPES allow a reliable determination of the mean valence of Yb ions. For YbAl2, it is evaluated to be +2.20, which remains nearly unchanged below 300 K. The Kondo resonance peak with an extremely high Kondo temperature (above 2000 K) is clearly identified in the valence-band spectra. The results indicate that a coherent Kondo state can be robust even in a nearly divalent system.
Nanoscale Dichotomy of Ti 3d Carriers Mediating the Ferromagnetism in Co:TiO2 Anatase Thin Films
T. Ohtsuki,A. Chainani,R. Eguchi,M. Matsunami,Y. Takata,M. Taguchi,Y. Nishino,K. Tamasaku,M. Yabashi,T. Ishikawa,M. Oura,Y. Senba,H. Ohashi,S. Shin
Physics , 2010, DOI: 10.1103/PhysRevLett.106.047602
Abstract: We study the surface and bulk electronic structure of the room-temperature ferromagnet Co:TiO2 anatase films using soft and hard x-ray photoemission spectroscopy with probe sensitivities of ~1 nm and ~10 nm, respectively. We obtain direct evidence of metallic Ti$^{3+}$ states in the bulk, which get suppressed to give a surface semiconductor, thus indicating a surface-bulk dichotomy. X-ray absorption and high-sensitivity resonant photoemission spectroscopy reveal Ti$^{3+}$ electrons at the Fermi level (E$_F$) and high-spin Co$^{2+}$ electrons occurring away from E$_F$. The results show the importance of the charge neutrality condition: Co$^{2+}$ + V$_{O}$$^{2-}$ + 2Ti$^{4+}$ $\leftrightarrow$ Co$^{2+}$ + 2Ti$^{3+}$ (V$_O$ is oxygen vacancy), which gives rise to the elusive Ti 3d carriers mediating ferromagnetism via the Co 3d-O 2p-Ti 3d exchange interaction pathway of the occupied orbitals.
Revisiting the valence-band and core-level photoemission spectra of NiO
M. Taguchi,M. Matsunami,Y. Ishida,R. Eguchi,A. Chainani,Y. Takata,M. Yabashi,K. Tamasaku,Y. Nishino,T. Ishikawa,Y. Senba,H. Ohashi,S. Shin
Physics , 2007, DOI: 10.1103/PhysRevLett.100.206401
Abstract: We have re-examined the valence-band (VB) and core-level electronic structure of NiO by means of hard and soft x-ray photoemission spectroscopy (PES). The spectral weight of the lowest energy state found to be enhanced in the bulk sensitive Ni 2p core-level PES. A configuration-interaction model including the bound state screening has shown significant agreement with the core-level spectra, and the off and on-resonance VB spectra. These results identify the lowest energy state in core-level and VB-PES as the Zhang-Rice doublet bound state, consistent with the spin-fermion model and recent ab initio calculation with dynamical mean-field theory (LDA + DMFT).
Prominent 5d-orbital contribution to the conduction electrons in gold
A. Sekiyama,J. Yamaguchi,A. Higashiya,M. Obara,H. Sugiyama,M. Y. Kimura,S. Suga,S. Imada,I. A. Nekrasov,M. Yabashi,K. Tamasaku,T. Ishikawa
Physics , 2010, DOI: 10.1088/1367-2630/12/4/043045
Abstract: We have examined the valence-band electronic structures of gold and silver in the same column in the periodic table with nominally filled d orbitals by means of a recently developed polarization-dependent hard x-ray photoemission. Contrary to a common expectation, it is found that the 5d-orbital electrons contribute prominently to the conduction electrons in gold while the conduction electrons in silver are to some extent free-electron-like with negligible 4d contribution, which could be related to a well-known fact that gold is more stable than silver in air. The 4d electron correlation effects are found to be essential for the conduction electron character in silver.
Electronic structures of CeRu$_2X_2$ ($X$ = Si, Ge) in the paramagnetic phase studied by soft X-ray ARPES and hard X-ray photoelectron spectroscopy
M. Yano,A. Sekiyama,H. Fujiwara,Y. Amano,S. Imada,T. Muro,M. Yabashi,K. Tamasaku,A. Higashiya,T. Ishikawa,Y. Onuki,S. Suga
Physics , 2007, DOI: 10.1103/PhysRevB.77.035118
Abstract: Soft and hard X-ray photoelectron spectroscopy (PES) has been performed for one of the heavy fermion system CeRu$_2$Si$_2$ and a $4f$-localized ferromagnet CeRu$_2$Ge$_2$ in the paramagnetic phase. The three-dimensional band structures and Fermi surface (FS) shapes of CeRu$_2$Si$_2$ have been determined by soft X-ray $h\nu$-dependent angle resolved photoelectron spectroscopy (ARPES). The differences in the Fermi surface topology and the non-$4f$ electronic structures between CeRu$_2$Si$_2$ and CeRu$_2$Ge$_2$ are qualitatively explained by the band-structure calculation for both $4f$ itinerant and localized models, respectively. The Ce valences in CeRu$_2X_2$ ($X$ = Si, Ge) at 20 K are quantitatively estimated by the single impurity Anderson model calculation, where the Ce 3d hard X-ray core-level PES and Ce 3d X-ray absorption spectra have shown stronger hybridization and signature for the partial $4f$ contribution to the conduction electrons in CeRu$_2$Si$_2$.
Hard x-ray photoemission study of LaAlO3/LaVO3 multilayers
H. Wadati,Y. Hotta,A. Fujimori,T. Susaki,H. Y. Hwang,Y. Takata,K. Horiba,M. Matsunami,S. Shin,M. Yabashi,K. Tamasaku,Y. Nishino,T. Ishikawa
Physics , 2007, DOI: 10.1103/PhysRevB.77.045122
Abstract: We have studied the electronic structure of multilayers composed of a band insulator LaAlO$_3$ (LAO) and a Mott insulator LaVO$_3$ (LVO) by means of hard x-ray photoemission spectroscopy, which has a probing depth as large as $\sim 60 {\AA}$. The Mott-Hubbard gap of LVO remained open at the interface, indicating that the interface is insulating unlike the LaTiO$_3$/SrTiO$_3$ multilayers. We found that the valence of V in LVO were partially converted from V$^{3+}$ to V$^{4+}$ only at the interface on the top side of the LVO layer and that the amount of V$^{4+}$ increased with LVO layer thickness. We suggest that the electronic reconstruction to eliminate the polarity catastrophe inherent in the polar heterostructure is the origin of the highly asymmetric valence change at the LVO/LAO interfaces.
Charge dynamics in strongly correlated one-dimensional Cu-O chain systems revealed by inelastic X-ray scattering
S. Suga,S. Imada,A. Higashiya,A. Shigemoto,S. Kasai,M. Sing,H. Fujiwara,A. Sekiyama,A. Yamasaki,C. Kim,T. Nomura,J. Igarashi,M. Yabashi,T. Ishikawa
Physics , 2005, DOI: 10.1103/PhysRevB.72.081101
Abstract: We report on the Cu 1s resonant inelastic X-ray scattering (RIXS) of Cu-O one-dimensional (1D) strongly correlated insulator systems with contrasting atomic arrangements, namely edge-sharing CuGeO3 and corner-sharing Sr2CuO3. Owing to good statistics of the high-resolution RIXS data, so far unresolved fine structures are revealed. Detailed photon-energy and momentum dependence of the RIXS spectra in comparison with theoretical calculations has clarified the natures of the low-energy charge excitations and hybridization of the electronic states.
High efficiency and low absorption Fresnel compound zone plates for hard X-ray focusing
A. Kuyumchyan,A. Isoyan,E. Shulakov,V. Aristov,M. Kondratenkov,A. Snigirev,I. Snigireva,A. Souvorov,K. Tamasaku,M. Yabashi,T. Ishikawa,K. Trouni
Computer Science , 2005, DOI: 10.1117/12.450480
Abstract: Circular and linear zone plates have been fabricated on the surface of silicon crystals for the energy of 8 keV by electron beam lithography and deep ion plasma etching methods. Various variants of compound zone plates with first, second, third diffraction orders have been made. The zone relief height is about 10 mkm, the outermost zone width of the zone plate is 0.4 mkm. The experimental testing of the zone plates has been conducted on SPring-8 and ESRF synchrotron radiation sources. A focused spot size and diffraction efficiency measured by knife-edge scanning are accordingly 0.5 mkm and 39% for the first order circular zone plate.
Evidence for the constancy of U in the Mott transition of V2O3
H. Fujiwara,A. Sekiyama,S. -K. Mo,J. W. Allen,J. Yamaguchi,G. Funabashi,S. Imada,P. Metcalf,A. Higashiya,M. Yabashi,K. Tamasaku,T. Ishikawa,S. Suga
Physics , 2009,
Abstract: We have performed high-resolution hard X-ray photoemission spectroscopy for the metal-insulator transition (MIT) system (V(1-x)Cr(x))2O3 in the paramagnetic metal, paramagnetic insulator and antiferromagentic insulator phases. The quality of the spectra enables us to conclude that the on-site Coulomb energy U does not change through the MIT, which eliminate all but one theoretical MIT scenario in this paradigm material.
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