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Journal Articles

Insight into Kondo screening in the intermediate-valence compound SmOs$$_4$$Sb$$_{12}$$ uncovered by soft X-ray magnetic circular dichroism

Saito, Yuji; Fujiwara, Hidenori*; Yasui, Akira*; Kadono, Toshiharu*; Sugawara, Hitoshi*; Kikuchi, Daisuke*; Sato, Hideyuki*; Suga, Shigemasa*; Yamasaki, Atsushi*; Sekiyama, Akira*; et al.

Physical Review B, 102(16), p.165152_1 - 165152_8, 2020/10

Journal Articles

Revising the 4${it f}$ symmetry in CeCu$$_{2}$$Ge$$_{2}$$; Soft X-ray absorption and hard X-ray photoemission spectroscopy

Aratani, Hidekazu*; Nakatani, Yasuhiro*; Fujiwara, Hidenori*; Kawada, Moeki*; Kanai, Yuina*; Yamagami, Kohei*; Fujioka, Shuhei*; Hamamoto, Satoru*; Kuga, Kentaro*; Kiss, Takayuki*; et al.

Physical Review B, 98(12), p.121113_1 - 121113_6, 2018/09

AA2018-0352.pdf:1.16MB

 Times Cited Count:3 Percentile:63.29(Materials Science, Multidisciplinary)

Journal Articles

Evidence for momentum-dependent heavy fermionic electronic structures; Soft X-ray ARPES for the superconductor CeNi$$_{2}$$Ge$$_{2}$$ in the normal state

Nakatani, Yasuhiro*; Aratani, Hidekazu*; Fujiwara, Hidenori*; Mori, Takeo*; Tsuruta, Atsushi*; Tachibana, Shoichi*; Yamaguchi, Takashi*; Kiss, Takayuki*; Yamasaki, Atsushi*; Yasui, Akira*; et al.

Physical Review B, 97(11), p.115160_1 - 115160_7, 2018/03

AA2018-0003.pdf:1.65MB

 Times Cited Count:1 Percentile:87.28(Materials Science, Multidisciplinary)

Journal Articles

Nanoscale spatial analysis of clay minerals containing cesium by synchrotron radiation photoemission electron microscopy

Yoshigoe, Akitaka; Shiwaku, Hideaki; Kobayashi, Toru; Shimoyama, Iwao; Matsumura, Daiju; Tsuji, Takuya; Nishihata, Yasuo; Kogure, Toshihiro*; Okochi, Takuo*; Yasui, Akira*; et al.

Applied Physics Letters, 112(2), p.021603_1 - 021603_5, 2018/01

 Times Cited Count:2 Percentile:74.71(Physics, Applied)

A synchrotron radiation photoemission electron microscope (SR-PEEM) was applied to demonstrate pinpoint analysis of micrometer-sized weathered biotite clay particles with artificially adsorbed cesium (Cs) atoms. Despite the insulating properties of the clay, we observed the spatial distributions of constituent elements (Si, Al, Cs, Mg, Fe) without charging issues. We found that Cs atoms were likely to be adsorbed evenly over the entire particle. Spatially-resolved X-ray absorption spectra (XAS) of the Cs M$$_{4,5}$$-edge region showed Cs to be present in a monocation state (Cs$$^{+}$$). Further pinpoint XAS measurements were also performed at the Fe L$$_{2,3}$$-edge to determine the chemical valence of the Fe atoms. Our results demonstrate the utility of SR-PEEM as a tool for spatially-resolved chemical analyses of various environmental substances, which is not limited by the poor conductivity of samples.

Journal Articles

Experimental observation of temperature and magnetic-field evolution of the 4${it f}$ states in CeFe$$_{2}$$ revealed by soft X-ray magnetic circular dichroism

Saito, Yuji; Yasui, Akira*; Fuchimoto, Hiroto*; Nakatani, Yasuhiro*; Fujiwara, Hidenori*; Imada, Shin*; Narumi, Yasuo*; Kindo, Koichi*; Takahashi, Minoru*; Ebihara, Takao*; et al.

Physical Review B, 96(3), p.035151_1 - 035151_5, 2017/07

AA2017-0611.pdf:0.36MB

 Times Cited Count:0 Percentile:100(Materials Science, Multidisciplinary)

We revisit the delocalized character of the 4$$f$$ states of CeFe$$_2$$ in the ferromagnetically ordered phase by X-ray magnetic circular dichroism (XMCD) in X-ray absorption spectroscopy (XAS) with improved data quality using single crystals. Surprisingly, the Ce $$M_{4,5}$$ XMCD spectral shape changes significantly as a function of temperature and applied magnetic field, with no concomitant changes in the spectral shape of the Ce $$M_{4,5}$$ XAS as well as the Fe $$L_{2,3}$$ XAS and XMCD. This unusual behavior is characterized by the $$J=7/2$$ states in a 4$$f^1$$ configuration mixed into the $$J=5/2$$ ground state. Such extreme sensitivity of the Ce 4$$f$$ states to the external perturbations can be related to the magnetic instability toward an antiferromagnetic phase in CeFe$$_2$$. Our experimental data presented here provide valuable insights into the underlying physics in strongly-hybridized ferromagnetic Ce compounds.

Journal Articles

Exotic hadrons from heavy ion collisions

Cho, S.*; Hyodo, Tetsuo*; Jido, Daisuke*; Ko, C. M.*; Lee, S. H.*; Maeda, Saori*; Miyahara, Kenta*; Morita, Kenji*; Nielsen, M.*; Onishi, Akira*; et al.

Progress in Particle and Nuclear Physics, 95, p.279 - 322, 2017/07

AA2016-0538.pdf:0.65MB

 Times Cited Count:37 Percentile:13.95(Physics, Nuclear)

With upgraded detectors at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC), it has become possible to measure hadrons beyond their ground states in high energy heavy ion collisions. Therefore, heavy ion collisions provide a new method for studying exotic hadrons that are either molecular states made of various hadrons or compact system consisting of muliquarks. Because their structures are related to the fundamental properties of Quantum Chromodynamics (QCD), studying exotic hadrons is currently one of the most active areas of research in hadron physics. The present review is a summary of the current understanding of a selected set of exotic candidate particles that can be potentially measured in heavy ion collisions.

Journal Articles

Circular dichroism in resonant angle-resolved photoemission spectra of LaNi$$_{2}$$Ge$$_{2}$$

Nakatani, Yasuhiro*; Fujiwara, Hidenori*; Aratani, Hidekazu*; Mori, Takeo*; Tachibana, Shoichi*; Yamaguchi, Takashi*; Kiss, Takayuki*; Yamasaki, Atsushi*; Yasui, Akira*; Yamagami, Hiroshi*; et al.

Journal of Electron Spectroscopy and Related Phenomena, 220, p.50 - 53, 2017/01

 Times Cited Count:1 Percentile:83.16(Spectroscopy)

We report the soft X-ray angle-resolved photoemission study for LaNi$$_{2}$$Ge$$_{2}$$ to reveal the electronic structures derived from non-4$$f$$ bands of the heavy fermion compound CeNi$$_{2}$$Ge$$_{2}$$. The photoemission spectra recorded at the La M$$_{4,5}$$ absorption edges clearly show the enhancement of the La 5$$d$$ components in the valence band spectra. The circular dichroism of photoemission spectra reveals the band-dependent dichroic response due to the orbital symmetry.

Journal Articles

Electronic structures of ferromagnetic CeAgSb$$_{2}$$; Soft X-ray absorption, magnetic circular dichroism, and angle-resolved photoemission spectroscopies

Saito, Yuji; Fujiwara, Hidenori*; Yamaguchi, Takashi*; Nakatani, Yasuhiro*; Mori, Takeo*; Fuchimoto, Hiroto*; Kiss, Takayuki*; Yasui, Akira*; Miyawaki, Jun*; Imada, Shin*; et al.

Journal of the Physical Society of Japan, 85(11), p.114713_1 - 114713_7, 2016/11

 Times Cited Count:7 Percentile:38.94(Physics, Multidisciplinary)

We report on the electronic structures of ferromagnetic CeAgSb$$_{2}$$ using soft X-ray absorption (XAS), magnetic circular dichroism (XMCD), and angle-resolved photoemission (ARPES) spectroscopies. The Ce $$M_{4,5}$$ XAS spectra show very small satellite structures, reflecting a strongly localized character of the Ce 4${it f}$ electrons. The linear dichroism effects in the Ce $$M_{4,5}$$ XAS spectra demonstrate the ground-state Ce 4${it f}$ symmetry of $$Gamma$$$$_{6}$$, the spatial distribution of which is directed along the ${it c}$-axis. Nevertheless, ARPES spectra at the Ce 3$$d$$-4$$f$$ resonance show the momentum dependence of the intensity ratio between Ce 4$$f^{1}_{5/2}$$ and 4$$f^{1}_{7/2}$$ peaks in a part of the Brillouin zone, suggesting the non negligible momentum-dependent hybridization effect between the Ce 4${it f}$ and the conduction electrons. This is associated with the moderate mass enhancement in CeAgSb$$_{2}$$.

Journal Articles

Electronic structures of ferromagnetic superconductors UGe$$_{2}$$ and UCoGe studied by angle-resolved photoelectron spectroscopy

Fujimori, Shinichi; Okochi, Takuo*; kawasaki, Ikuto*; Yasui, Akira*; Takeda, Yukiharu; Okane, Tetsuo; Saito, Yuji; Fujimori, Atsushi; Yamagami, Hiroshi; Haga, Yoshinori; et al.

Physical Review B, 91(17), p.174503_1 - 174503_9, 2015/05

 Times Cited Count:17 Percentile:28.75(Materials Science, Multidisciplinary)

The electronic structures of the ferromagnetic superconductors UGe$$_2$$ and UCoGe in the paramagnetic phase were studied by angle-resolved photoelectron spectroscopy using soft X-rays ($$h nu$$ = 400-500 eV). The quasi-particle bands with large contributions from U 5$$f$$ states were observed in the vicinity of EF, suggesting that the U 5$$f$$ electrons of these compounds have an itinerant character. Their overall band structures were explained by the band-structure calculations treating all the U 5$$f$$ electrons as being itinerant. Meanwhile, the states in the vicinity of EF show considerable deviations from the results of band-structure calculations, suggesting that the shapes of Fermi surface of these compounds are qualitatively different from the calculations, possibly caused by electron correlation effect in the complicated band structures of the low-symmetry crystals. Strong hybridization between U 5$$f$$ and $$mathrm{Co} 3d$$ states in UCoGe were found by the $$mathrm{Co}$$ 2p-3d resonant photoemission experiment, suggesting that $$mathrm{Co} 3d$$ states have finite contributions to the magnetic, transport, and superconducting properties.

Journal Articles

Probing strongly correlated 4$$f$$-orbital symmetry of the ground state in Yb compounds by linear dichroism in core-level photoemission

Mori, Takeo*; Kitayama, Satoshi*; Kanai, Yuina*; Naimen, Sho*; Fujiwara, Hidenori*; Higashiya, Atsushi*; Tamasaku, Kenji*; Tanaka, Arata*; Terashima, Kensei*; Imada, Shin*; et al.

Journal of the Physical Society of Japan, 83(12), p.123702_1 - 123702_5, 2014/12

 Times Cited Count:14 Percentile:27.43(Physics, Multidisciplinary)

We show that the strongly correlated 4$$f$$-orbital symmetry of the ground state is revealed by linear dichroism in core-level photoemission spectra, as we have discovered for YbRh$$_{2}$$Si$$_{2}$$ and YbCu$$_{2}$$Si$$_{2}$$. Theoretical analysis shows us that the linear dichroism reflects the anisotropic charge distributions resulting from a crystalline electric field. We have successfully determined the ground-state 4$$f$$ symmetry for both compounds from the polarization-dependent angle resolved core-level spectra at a temperature well below the first excitation energy. The excited-state symmetry is also probed by temperature dependence of the linear dichroism where the high measurement temperatures are on the order of the crystal-field-splitting energies.

Journal Articles

Angle resolved photoelectron spectroscopy study of heavy fermion superconductor UPd$$_{2}$$Al$$_{3}$$

Fujimori, Shinichi; kawasaki, Ikuto*; Yasui, Akira*; Takeda, Yukiharu; Okane, Tetsuo; Saito, Yuji; Fujimori, Atsushi; Yamagami, Hiroshi; Haga, Yoshinori; Yamamoto, Etsuji; et al.

JPS Conference Proceedings (Internet), 3, p.011072_1 - 011072_5, 2014/06

In this presentation, we review some of our recent photoemission studies on uranium superconductors by means of soft X-ray synchrotron radiation ARPES (SX-ARPES). Results of SX-ARPES study on URhGe and UPd$$_{2}$$Al$$_{3}$$ will be presented. URhGe is a ferromagnetic superconductor with $$T_{rm Curie}$$ = 9.5 K and $$T_{rm SC}$$ = 0.26 K while UPd$$_{2}$$Al$$_{3}$$ is an antiferromagnetic superconductor with $$T_{rm N}$$ = 14 K and $$T_{rm SC}$$ = 1.8 K. We have revealed the three-dimensional electronic structures of those compounds by SX-ARPES, and they are compared with those calculated by LDA.

Journal Articles

Itinerant magnetism in URhGe revealed by angle-resolved photoelectron spectroscopy

Fujimori, Shinichi; kawasaki, Ikuto*; Yasui, Akira*; Takeda, Yukiharu; Okane, Tetsuo; Saito, Yuji; Fujimori, Atsushi*; Yamagami, Hiroshi; Haga, Yoshinori; Yamamoto, Etsuji; et al.

Physical Review B, 89(10), p.104518_1 - 104518_7, 2014/03

 Times Cited Count:17 Percentile:31.11(Materials Science, Multidisciplinary)

The electronic structure of the ferromagnetic superconductor URhGe in the paramagnetic phase has been studied by angle-resolved photoelectron spectroscopy using soft X rays ($$hnu$$ = 595-700 eV). Dispersive bands with large contributions from U 5$$f$$ states were observed in the ARPES spectra, and form Fermi surfaces. The band structure in the paramagnetic phase is partly explained by the band-structure calculation treating all U 5$$f$$ electrons as being itinerant, suggesting that an itinerant description of U 5$$f$$ states is a good starting point for this compound. On the other hand, there are qualitative disagreements especially in the band structure near the Fermi level ($$E$$$$_{rm B}$$ $$_sim^{<}$$ 0.5 eV). The experimentally observed bands are less dispersive than the calculation, and the shape of the Fermi surface is different from the calculation. The changes in spectral functions due to the ferromagnetic transition were observed in bands near the Fermi level, suggesting that the ferromagnetism in this compound has an itinerant origin.

Journal Articles

Direct $$kappa$$-space mapping of the electronic structure in an oxide-oxide interface

Berner, G.*; Sing, M.*; Fujiwara, Hidenori*; Yasui, Akira*; Saito, Yuji; Yamasaki, Atsushi*; Nishitani, Yoshihito*; Sekiyama, Akira*; Pavlenko, N.*; Kopp, T.*; et al.

Physical Review Letters, 110(24), p.247601_1 - 247601_5, 2013/06

 Times Cited Count:104 Percentile:2.9(Physics, Multidisciplinary)

The interface between LaAlO$$_{3}$$ and SrTiO$$_{3}$$ hosts a two-dimensional electron system of itinerant carriers, although both oxides are band insulators. Interface ferromagnetism coexisting with superconductivity has been found and attributed to local moments. Experimentally, it has been established that Ti 3$$d$$ electrons are confined to the interface. Using soft X-ray angle-resolved resonant photoelectron spectroscopy we have directly mapped the interface states in $$kappa$$ space. Our data demonstrate a charge dichotomy. A mobile fraction contributes to Fermi surface sheets, whereas a localized portion at higher binding energies is tentatively attributed to electrons trapped by O vacancies in the SrTiO$$_{3}$$.

Journal Articles

Observation of bulk band dispersions of YbRh$$_2$$Si$$_2$$ using soft X-ray angle-resolved photoemission spectroscopy

Yasui, Akira*; Saito, Yuji; Fujimori, Shinichi; kawasaki, Ikuto*; Okane, Tetsuo; Takeda, Yukiharu; Lapertot, G.*; Knebel, G.*; Matsuda, Tatsuma*; Haga, Yoshinori; et al.

Physical Review B, 87(7), p.075131_1 - 075131_6, 2013/02

 Times Cited Count:5 Percentile:69.24(Materials Science, Multidisciplinary)

We have performed soft X-ray angle-resolved photoemission spectroscopy (ARPES) measurements on YbRh$$_2$$Si$$_2$$ and clarified its three-dimensional bulk valence-band structures. The ARPES spectra have not only Yb$$^{3+}$$ multiplet peaks but also a finite contribution of Yb$$^{2+}$$ peaks at 15 K, corresponding to the valence fluctuating behavior in this compound. This means that Yb 4f electrons in this compound have itinerant character below the $$T_{rm K}$$. We have found that dispersions of the valence bands except the vicinity of the Yb 4f bands agree better with those of the band-structure calculation of LuRh$$_2$$Si$$_2$$ than those of YbRh$$_2$$Si$$_2$$ within a local-density approximation. In addition, the Yb 3d-4f resonant photoemission spectra of YbRh$$_2$$Si$$_2$$ strongly suggest the existence of Yb 5d electrons in the valence band. We conclude that the charge transfer from the Yb 4f state to the Yb 5d state has an important role in the formation of the valence band of YbRh$$_2$$Si$$_2$$.

Journal Articles

Electronic structure of heavy fermion uranium compounds studied by core-level photoelectron spectroscopy

Fujimori, Shinichi; Okochi, Takuo*; Kawasaki, Ikuto; Yasui, Akira; Takeda, Yukiharu; Okane, Tetsuo; Saito, Yuji; Fujimori, Atsushi; Yamagami, Hiroshi; Haga, Yoshinori; et al.

Journal of the Physical Society of Japan, 81(1), p.014703_1 - 014703_9, 2012/01

 Times Cited Count:31 Percentile:16.68(Physics, Multidisciplinary)

High-energy-resolution core-level and valence-band photoelectron spectroscopic studies were performed for the heavy Fermion uranium compounds UGe$$_2$$, UCoGe, URhGe, URu$$_2$$Si$$_2$$, UNi$$_2$$Al$$_3$$, UPd$$_2$$Al$$_3$$, and UPt$$_3$$ as well as typical localized and itinerant uranium compounds to understand the relationship between the uranium valence state and their core-level spectral line shapes. The core-level spectra of UGe$$_2$$, UCoGe, URhGe, URu$$_2$$Si$$_2$$, and UNi$$_2$$Al$$_3$$ are rather similar to those of itinerant compounds, suggesting that U 5$$f$$ electrons in these compounds are well hybridized with ligand states. On the other hand, the core-level spectra of UPd$$_2$$Al$$_3$$ and UPt$$_3$$ show considerably different spectral line shapes from those of the itinerant compounds, suggesting that U 5$$f$$ electrons in UPd$$_2$$Al$$_3$$ and UPt$$_3$$ are less hybridized with ligand states, leading to the correlated nature of U 5$$f$$ electrons in these compounds.

Journal Articles

Itinerant U 5$$f$$ nature in antiferromagnet U(Ru$$_{0.97}$$Rh$$_{0.03}$$)$$_{2}$$Si$$_{2}$$; Soft X-ray angle-resolved photoemission spectroscopy

Kawasaki, Ikuto; Fujimori, Shinichi; Okane, Tetsuo; Yasui, Akira; Saito, Yuji; Yamagami, Hiroshi*; Haga, Yoshinori; Yamamoto, Etsuji; Onuki, Yoshichika*

Journal of the Physical Society of Japan, 80(12), p.124710_1 - 124710_5, 2011/12

 Times Cited Count:4 Percentile:62.54(Physics, Multidisciplinary)

We have carried out soft X-ray angle-resolved photoemission spectroscopy experiments on U(Ru$$_{0.97}$$Rh$$_{0.03}$$)$$_{2}$$Si$$_{2}$$, which shows antiferromagnetic (AFM) ordering at low temperatures. We have revealed that U 5$$f$$ electrons contribute to the formation of the energy band as well as Fermi surface. This suggests that the AFM ordering is caused by a spin density wave of itinerant U 5$$f$$ electrons. The observed band dispersion and Fermi surface are nearly identical to those of URu$$_{2}$$Si$$_{2}$$. Therefore, the AFM ordering vector $$Q$$ = (1,0,0) can be a possible ordering vector of the hidden order phase in URu$$_{2}$$Si$$_{2}$$.

Journal Articles

Electronic structure of YbCu$$_2$$Ge$$_2$$ studied by soft X-ray angle-resolved photoemission spectroscopy

Yasui, Akira; Fujimori, Shinichi; Kawasaki, Ikuto; Okane, Tetsuo; Takeda, Yukiharu; Saito, Yuji; Yamagami, Hiroshi; Sekiyama, Akira*; Settai, Rikio*; Matsuda, Tatsuma; et al.

Physical Review B, 84(19), p.195121_1 - 195121_6, 2011/11

 Times Cited Count:7 Percentile:62.71(Materials Science, Multidisciplinary)

We have measured three-dimensional band structure and Fermi surfaces (FSs) of YbCu$$_2$$Ge$$_2$$, which has recently become recognized as a nearly divalent Yb-based compound, by using soft X-ray angle-resolved photoemission spectroscopy. We clarified that the bands with finite Yb 4$$f$$ contribution cross the Fermi level and are slightly involved in the formation of the FSs, in line with the valence-fluctuating state of YbCu$$_2$$Ge$$_2$$. The obtained valence-band dispersions and the FSs are well explained by a relativistic band-structure calculation based on a local-density-approximation (LDA). These results suggest that the LDA calculation is a good starting point for understanding of the electronic state of YbCu$$_2$$Ge$$_2$$ as well as nearly divalent Yb-based compounds.

Journal Articles

Resonant angle-resolved photoelectron spectroscopy of substitutional solid solutions of CeRu$$_2$$Si$$_2$$

Okane, Tetsuo; Kawasaki, Ikuto; Yasui, Akira; Okochi, Takuo*; Takeda, Yukiharu; Fujimori, Shinichi; Saito, Yuji; Yamagami, Hiroshi; Fujimori, Atsushi; Matsumoto, Yuji*; et al.

Journal of the Physical Society of Japan, 80(Suppl.A), p.SA060_1 - SA060_3, 2011/07

 Times Cited Count:1 Percentile:87.38(Physics, Multidisciplinary)

Journal Articles

Soft X-ray angle-resolved photoemission study of YbCu$$_2$$Ge$$_2$$

Yasui, Akira; Fujimori, Shinichi; Kawasaki, Ikuto; Okane, Tetsuo; Takeda, Yukiharu; Saito, Yuji; Yamagami, Hiroshi; Sekiyama, Akira*; Settai, Rikio*; Matsuda, Tatsuma; et al.

Journal of Physics; Conference Series, 273, p.012067_1 - 012067_4, 2011/02

 Times Cited Count:3 Percentile:31.67

Soft X-ray photoemission spectroscopies have been performed on YbCu$$_2$$Ge$$_2$$, which is thought to be a Yb divalent system, to investigate its bulk electronic structure including Yb 4$$f$$ electrons. Small but finite Yb$$^{3+}$$ multiplet peaks were found at 6$$sim$$12 eV in the angle-integrated spectrum, suggesting that it is a valence fluctuation compound. An "anti-crossing" Yb 4$$f$$ bands with conduction bands were observed in the angle-resolved spectrum. This is the evidence that the Yb 4$$f$$ electrons form a band state through the hybridization with Ge 4$$p$$ and Cu 3$$d$$ electrons.

Journal Articles

Magnetic and superconducting properties of CeRhGe$$_2$$ and CePtSi$$_2$$

Hirose, Yusuke*; Nishimura, Naoto*; Honda, Fuminori*; Sugiyama, Kiyohiro*; Hagiwara, Masayuki*; Kindo, Koichi*; Takeuchi, Tetsuya*; Yamamoto, Etsuji; Haga, Yoshinori; Matsuura, Masato*; et al.

Journal of the Physical Society of Japan, 80(2), p.024711_1 - 024711_12, 2011/02

 Times Cited Count:5 Percentile:57(Physics, Multidisciplinary)

53 (Records 1-20 displayed on this page)