H. Iwasawa, K. Yamakawa, T. Saitoh, ∗ J. Inaba, T. Katsufuji, 4 M. Higashiguchi, K. Shimada, H. Namatame, and M. Taniguchi Department of Applied Physics, Tokyo University of Science, Shinjuku-ku, Tokyo 162-8601, Japan National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8568, Japan Department of Physics, Waseda University, Tokyo 169-8555, Japan PRESTO, Japan Science and Technology Corporation, Saitama 332-0012, Japan Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima 739-8526, Japan (Dated: May 27, 2021)

D. Ootsuki, S. Pyon, K. Kudo, M. Nohara, M. Horio, T. Yoshida, A. Fujimori, M. Arita, H. Anzai, H. Namatame, M. Taniguchi, N. L. Saini, and T. Mizokawa Department of Complexity Science and Engineering & Department of Physics, University of Tokyo, 5-1-5 Kashiwanoha, Chiba 277-8561, Japan Department of Physics, Okayama University, Kita-ku, Okayama 700-8530, Japan Department of Physics, University of Tokyo, 7-3-1 Hongo, Tokyo 113-0033, Japan Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-hiroshima 739-0046, Japan Graduate School of Science, Hiroshima University, Higashi-hiroshima 739-8526, Japan and Department of Physics, University of Roma ”La Sapienza” Piazzale Aldo Moro 2, 00185 Roma, Italy (Dated: October 12, 2020)

The emergence of quantization at the nanoscale, the quantum size effect (QSE), allows flexible control of matter and is a rich source of advanced functionalities. A QSE-induced transition into an insulating phase in semimetallic nanofilms was predicted for bismuth a half-century ago and has regained new interest with regard to its surface states exhibiting nontrivial electronic topology. Here, we reveal an unexpected mechanism of the transition by high-resolution angle-resolved photoelectron spectroscopy combined with theoretical calculations. Anomalous evolution and degeneracy of quantized energy levels indicate that increased Coulomb repulsion from the surface states deforms a quantum confinement potential with decreasing thickness. The potential deformation strongly modulates spatial distributions of quantized wave functions, which leads to acceleration of the transition beyond the original QSE picture. This discovery establishes a complete picture of the long-discussed transition and highlights a new class of size effects dominating nanoscale transport in systems with metallic surface states.

We have performed an angle-resolved photoemission study of the nodal quasi-particle spectra of the high-Tc cuprate tri-layer Bi2Sr2Ca2Cu3O10+δ (Tc ∼ 110 K). The spectral weight Z of the nodal quasi-particle increases with decreasing temperature across the Tc. Such a temperature dependence is qualitatively similar to that of the coherence peak intensity in the anti-nodal region of various high-Tc cuprates although the nodal spectral weight remains finite and large above Tc. We attribute this observation to the reduction of electron correlation strength in going from the normal metallic state to the superconducting state, a characteristic behavior of a superconductor with strong electron correlation.

We have studied the electronic structure of SnSe and Na-doped SnSe by means of angle-resolved photoemission spectroscopy. The valence-band top reaches the Fermi level by the Na doping, indicating that Na-doped SnSe can be viewed as a degenerate semiconductor. However, in the Na-doped system, the chemical potential shift with temperature is unexpectedly large and is apparently inconsistent with the degenerate semiconductor picture. The large chemical potential shift and anomalous spectral shape are key ingredients for an understanding of the novel metallic state with the large thermoelectric performance in Na-doped SnSe.

Alkali-metal adsorption on the surface of materials is widely used for in situ surface electron doping, particularly for observing unoccupied band structures by angle-resolved photoemission spectroscopy (ARPES). However, the effects of alkali-metal atoms on the resulting band structures have yet to be fully investigated, owing to difficulties in both experiments and calculations. Here, we combine ARPES measurements on cesium-adsorbed ultrathin bismuth films with first-principles calculations of the electronic charge densities and demonstrate a simple method to evaluate alkali-metal induced band deformation. We reveal that deformation of bismuth surface bands is directly correlated with vertical charge-density profiles at each electronic state of bismuth. In contrast, a change in the quantized bulk bands is well described by a conventional rigid-band-shift picture. We discuss these two aspects of the band deformation holistically, considering spatial distributions of the electronic states and cesium-bismuth hybridization, and provide a prescription for applying alkali-metal adsorption to a wide range of materials.

We have grown the phase-homogeneous ternary compound with composition Bi2Te1.85S1.15 very close to the stoichiometric Bi2Te2S. The measurements performed with spin-and angle-resolved photoelectron spectroscopy as well as density functional theory andGW calculations revealed awide-band-gap three-dimensional topological insulator phase. The surface electronic spectrum is characterized by the topological surface state (TSS) with Dirac point located above the valence band and Fermi level lying in the band gap. TSS band dispersion and constant energy contour manifest a weak warping effect near the Fermi level along with in-plane and out-of-plane spin polarization along the (Gamma) over bar-(K) over bar line. We identified four additional states at deeper binding energies with high in-plane spin polarization.

We have carried out hard x-ray photoemission spectroscopy (HAXPES) of Yb1-x Zr x B12 ([Formula: see text]) to study the effects of electron doping on the Kondo insulator YbB12. The Yb valences of Yb1-x Zr x B12 at 300 K estimated from the Yb 3d HAXPES spectra decreased after substituting Yb with Zr from 2.93 for YbB12 to 2.83 for Yb0.125Zr0.875B12. A temperature dependent valence decrease was found upon cooling for all doping concentrations. We found peak shifts of the B 1s and Zr 3d5/2, and Yb3+ 4f spectra toward the deeper binding-energy with increasing Zr concentration, which indicates a shift of the Fermi level to the higher energy and that of the Yb 4f hole level close to the Fermi level, respectively, due to electron doping. These results qualitatively show the enhanced hybridization between the Yb 4f and conduction-band states with Zr substitution, consistent with magnetic susceptibility measurements.

Background: As was reported, gefitinib (Iressa®) showed a strong growth inhibitory effect on non-small-cell lung cancer PC-9 cells with mutant EGFR, but did not so much on A549 cells with wild-type EGFR. Observation: We here demonstrated by isobolograms and combination index analyses that the paired combinations of gefitinib with flavonoids from Wogon (Scutellaria baicalensis root): wogonin, oroxylin A and chrysin exerted synergistic anti-tumor effects against A549 cells. Result: The cell cycle analyses revealed that the combination of gefitinib and oroxylin A in A549 cells induced more apoptotic cells than other paired combinations as well as gefitinib alone. Thus, it is anticipated that oroxylin A could help to enhance the remission rate in the gefitinib therapy for the patients with non-small cell cancer cells with wild-type EGFR which provide a poor prognosis. Conclusion: Since the Wogon flavonoids, wogonin, oroxylin A and chrysin, accelerated the acetylation of Lysine residues of histone proteins, it is suggested that they put forth anti-tumor activities through inhibition of histone deacetylases which mediated the post-translational modification of histones.

RESEARCH ARTICLE Synergistic Antitumor Effect of Genitinib (Iressa) with Flavonoids from the Scutellaria baicalensis Root on the Non-Small Cell Lung Cells Y. Hirata, M. Tatsu, C. Amano, Y. Kawaratani, M. Hirata, Y. Ohmomo, Y. Nagaoka, M. Shibano, T. Sasaki, S. Uesato and M. Taniguchi Division of Pharmaceutical Science, Osaka University of Pharmaceutical Sciences, 4-20-1 Nasahara, Takatsuki, Osaka 569-1094, Japan. Department of Life Science and Biotechnology, Faculty of Chemistry, Materials and Bioengineering, Kansai University, Suita, Osaka 564-8680, Japan. Department of Neurology, Graduate School of Medicine, Osaka University, Yamadaoka 2-2, Suita, Osaka 565-0871, Japan.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

A rotatable high-resolution angle-resolved photoemission spectroscopy (ARPES) system has been developed to utilize tunable linear-polarization geometries on the linear undulator beamline (BL-1) at Hiroshima Synchrotron Radiation Center. By rotating the whole ARPES measurement system, the photoelectron detection plane can be continuously changed from parallel to normal against the electric field vector of linearly polarized undulator radiation. This polarization tunability enables us to identify the symmetry of the initial electronic states with respect to the mirror planes, and to selectively observe the electronic states based on the dipole selection rule in the photoemission process. Specifications of the rotatable high-resolution ARPES system are described, as well as its capabilities with some representative experimental results.

We have investigated the electronic structures of Y1-xTmxB6 (x = 0, 0.25) and Yb1-xTmxB6 (x = 0, 0.2) by means of hard x-ray photoemission spectroscopy (HAXPES) at h v = 5.95 key. The Tm 3d HAXPES revealed that the valence of Tm in YB6 is similar to 2.6 at 300 K and similar to 2.5 at 20 K, indicating strong valence fluctuation. In contrast, Tm in YbB6 is almost trivalent independent of temperature. Yb in YbB6 is almost divalent and the Yb2+ state is stabilized by the Tm doping. (C) 2017 Elsevier B.V. All rights reserved.

We studied the electronic structure of EuNi2P2, which exhibits both heavy-fermion and mixed-valence behaviors, using angle-resolved photoemission spectroscopy. Multiple Ni 3d bands were observed near the Fermi energy, and one of them forms a hole-like Fermi surface around the X point of the Brillouin zone. We also found that the spectral weight of the Ni 3d states is rapidly enhanced with decreasing temperature, which is consistent with the temperature dependence of the mean valence of Eu ions. Our results thus demonstrate hybridization between the Ni 3d and Eu 4f electrons in EuNi2P2.

In the hole-doped cuprates, a small number of carriers suppresses antiferromagnetism and induces superconductivity. In the electron-doped cuprates, on the other hand, superconductivity appears only in a narrow window of high-doped Ce concentration after reduction annealing, and strong antiferromagnetic correlation persists in the superconducting phase. Recently, Pr1.3-xLa0.7CexCuO4 (PLCCO) bulk single crystals annealed by a protect annealing method showed a high critical temperature of around 27 K for small Ce content down to 0.05. Here, by angle-resolved photoemission spectroscopy measurements of PLCCO crystals, we observed a sharp quasi-particle peak on the entire Fermi surface without signature of an antiferromagnetic pseudogap unlike all the previous work, indicating a dramatic reduction of antiferromagnetic correlation length and/or of magnetic moments. The superconducting state was found to extend over a wide electron concentration range. The present results fundamentally challenge the long-standing picture on the electronic structure in the electron-doped regime.

The three-dimensional（3D） Dirac semimetals have linearly dispersive 3D Dirac nodes where the conduction band and valence band are connected. They have isolated 3D Dirac nodes in the whole Brillouin zone and can be viewed as a 3D counterpart of graphene. Recent theoretical calculations and experimental results indicate that the 3D Dirac semimetal state can be realized in a simple stoichiometric compound A3Bi（A = Na, K, Rb）. Here we report comprehensive high-resolution angle-resolved photoemission（ARPES） measurements on the two cleaved surfaces,（001） and（100）, of Na3Bi. On the（001） surface, by comparison with theoretical calculations, we provide a proper assignment of the observed bands, and in particular, pinpoint the band that is responsible for the formation of the three-dimensional Dirac cones. We observe clear evidence of 3D Dirac cones in the three-dimensional momentum space by directly measuring on the kx–ky plane and by varying the photon energy to get access to different out-of-plane kzs. In addition, we reveal new features around the Brillouin zone corners that may be related with surface reconstruction. On the（100） surface, our ARPES measurements over a large momentum space raise an issue on the selection of the basic Brillouin zone in the（100） plane. We directly observe two isolated 3D Dirac nodes on the（100） surface. We observe the signature of the Fermi-arc surface states connecting the two 3D Dirac nodes that extend to a binding energy of 150 me V before merging into the bulk band. Our observations constitute strong evidence on the existence of the Dirac semimetal state in Na3Bi that are consistent with previous theoretical and experimental work. In addition, our results provide new information to clarify on the nature of the band that forms the3 D Dirac cones, on the possible formation of surface reconstruction of the（001） surface, and on the issue of basic Brillouin zone selection for the（100） surface.

We use a surface-selective angle-resolved photoemission spectroscopy and unveil the electronic nature on the topmost layer of Sr_{2}RuO_{4} crystal, consisting of slightly rotated RuO_{6} octahedrons. The γ band derived from the 4d_{xy} orbital is found to be about three times narrower than that for the bulk. This strongly contrasts with a subtle variation seen in the α and β bands derived from the one-dimensional 4d_{xz/yz}. This anomaly is reproduced by the dynamical mean-field theory calculations, introducing not only the on-site Hubbard interaction but also the significant Hund's coupling. We detect a coherence-to-incoherence crossover theoretically predicted for Hund's metals, which has been recognized only recently. The crossover temperature in the surface is about half that of the bulk, indicating that the naturally generated monolayer of reconstructed Sr_{2}RuO_{4} is extremely correlated and well isolated from the underlying crystal.

Two-dimensional (2D) metallic states formed on the ZnO(10 (1) over bar0) surface by hydrogen adsorption have been investigated using angle-resolved photoelectron spectroscopy (ARPES). The observed metallic state is characterized by a peak-dip-hump structure at just below the Fermi level and a long tail structure extending up to 600 meV in binding energy. The peak and hump positions are separated by about 70 meV, a value close to the excitation energy of longitudinal optical (LO) phonons. Spectral functions formulated on the basis of the 2D electron-phonon coupling well reproduce the ARPES intensity distribution of the metallic states. This spectral analysis suggests that the 2D electrons accumulated on the ZnO surface couple to the LO phonons and that this coupling is the origin of the anomalous long tail. Our results indicate that the 2D electrons at the ZnO surface are described as the electron liquid model.

Vulcanized rubber materials are useful in our surroundings. However, detail structure and reaction are not revealed even in present. Since squalene molecule possesses some same properties compared with natural rubber, we have prepared the samples of vulcanized squalene at 140 °C for several hours. To understand the vulcanization reaction,sulfur K-edge NEXAFS measurements have been carried out for the vulcanized squalene under liquid phase with He-path system and fluorescence detection mode. Moreover, we have tried curve fitting analysis of NEXAFS spectra. The results indicate that the squalene has been vulcanized by the S8 molecule at 140 °C and the S8 molecule length is shortened from 8 to 5-6 after the vulcanization reaction.

We have investigated the electronic structure of BiS2-based CeO0.5F0.5BiS2 superconductor using polarization-dependent angle-resolved photoemission spectroscopy (ARPES), and succeeded in elucidating the orbital characters on the Fermi surfaces. In the rectangular Fermi pockets around the X point, the straight portion parallel to the k(y) direction is dominated by Bi 6p(x) character. The orbital polarization indicates the underlying quasi-one-dimensional electronic structure of the BiS2 system. Moreover, distortions on tetragonally aligned Bi could give rise to the band Jahn-Teller effect.