290 results on '"Takayoshi Yokoya"'
Search Results
2. Superconductivity in the α-Form Layer Structured Metal Nitride Halide
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Masashi Tanaka, Noriyuki Kataoka, and Takayoshi Yokoya
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α-form layered nitride halides ,intercalation ,electron doping ,superconducting mechanism ,photoemission spectroscopy ,Physics ,QC1-999 - Abstract
Layered metal nitride halides MNX (M = Ti, Zr, Hf; X = Cl, Br, I) have two polymorphs, including α- and β-forms, which have the FeOCl and SmSI structures, respectively. These compounds are band insulators and become metals and show superconductivity after electron doping by intercalating alkali metals between the layers. The superconductivity of β-form had been extensively characterized from decades ago, but it is not easy to consistently interpret all experimental results using conventional phonon-mediated Bardeen–Cooper–Schriefer mechanisms. The titanium compound TiNCl crystallizes only in the α-form structure. TiNCl also exhibits superconductivity as high as ~16 K after electron doping by intercalating metals and/or organic basis. It is important to compare the superconductivity of different M–N networks. However, α-form compounds are vulnerable to moisture, unlike β-form ones. The intercalation compounds are even more sensitive to humid air. Thus, there are few experimental studies on the superconducting mechanism of α-form, although it has been discussed for exotic Cooper-pairing mechanisms. This short review gathers the recent progress in experimental studies of TiNCl.
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- 2022
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3. Synthesis and Characterization of a Trigonal Layered Compound AgInS2
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Takahiro Sawahara, Ryo Matsumoto, Yuki Nakahira, Hidetomo Usui, Noriyuki Kataoka, Ryusei Saitou, Takanori Wakita, Takayoshi Yokoya, Aichi Yamashita, Yosuke Goto, Yoshihiko Takano, Akira Miura, and Yoshikazu Mizuguchi
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General Chemical Engineering ,General Chemistry - Published
- 2023
4. Controlling of Localization by Elemental-substitution Effect in Layered BiCh2-based Compounds LaO1−xFxBiS2−ySey
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Kazuhisa Hoshi, Hiroto Arima, Noriyuki Kataoka, Masayuki Ochi, Aichi Yamashita, Anne de Visser, Takayoshi Yokoya, Kazuhiko Kuroki, and Yoshikazu Mizuguchi
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General Physics and Astronomy - Published
- 2023
5. Photoelectron Holography Study of La(O,F)BiS2
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YaJun Li, ZeXu Sun, Noriyuki Kataoka, Taro Setoguchi, Yusuke Hashimoto, Soichiro Takeuchi, Shunjo Koga, Satoshi Demura, Kanako Noguchi, Hideaki Sakata, Yoshikazu Mizuguchi, Tomohiro Matsushita, Takanori Wakita, Yuji Muraoka, and Takayoshi Yokoya
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General Physics and Astronomy - Published
- 2023
6. Photoelectron Diffraction and Holography Studies on Dopant Local Structures
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Takayoshi Yokoya
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General Physics and Astronomy - Published
- 2022
7. Anomalously large spin-dependent electron correlation in the nearly half-metallic ferromagnet CoS2
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Hirokazu Fujiwara, Kensei Terashima, Junya Otsuki, Nayuta Takemori, Harald O. Jeschke, Takanori Wakita, Yuko Yano, Wataru Hosoda, Noriyuki Kataoka, Atsushi Teruya, Masashi Kakihana, Masato Hedo, Takao Nakama, Yoshichika Ōnuki, Koichiro Yaji, Ayumi Harasawa, Kenta Kuroda, Shik Shin, Koji Horiba, Hiroshi Kumigashira, Yuji Muraoka, and Takayoshi Yokoya
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- 2022
8. Incorporation Site and Valence State of Sn Atoms in Sn-Substituted La(O,F)BiS2 Superconductor
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YaJun Li, ZeXu Sun, Noriyuki Kataoka, Taro Setoguchi, Yusuke Hashimoto, Soichiro Takeuchi, Shunjo Koga, Takayuki Muro, Satoshi Demura, Kanako Noguchi, Hideaki Sakata, Tomohiro Matsushita, Ikuto Kawasaki, Shin-ichi Fujimori, Takanori Wakita, Yuji Muraoka, and Takayoshi Yokoya
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General Physics and Astronomy - Published
- 2022
9. Self-organized vertical multilayer structures in spinodally decomposed TiO2-VO2 films on glass substrates
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Yuji Muraoka, Kazutada Takeda, Yoshito Takemoto, Takanori Wakita, and Takayoshi Yokoya
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Materials Chemistry ,Metals and Alloys ,Surfaces and Interfaces ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials - Published
- 2023
10. Formation of Q-carbon by adjusting sp3 content in diamond-like carbon films and laser energy density of pulsed laser annealing
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Takayoshi Yokoya, Yuji Muraoka, Takanori Wakita, Seiko Inubushi, and Hiroki Yoshinaka
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Q-carbon ,Materials science ,Diamond-like carbon ,medicine.medical_treatment ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,law.invention ,Pulsed laser deposition ,symbols.namesake ,law ,medicine ,General Materials Science ,Excimer laser ,business.industry ,General Chemistry ,021001 nanoscience & nanotechnology ,Laser ,0104 chemical sciences ,Amorphous solid ,Sapphire ,symbols ,Optoelectronics ,0210 nano-technology ,business ,Raman spectroscopy - Abstract
In this study, we prepared Q-carbon by adjusting the sp3 content in diamond-like carbon (DLC) films and the laser energy density of pulsed laser annealing (PLA). The amorphous DLC films were fabricated on sapphire Al2O3(0001) substrates using a pulsed laser deposition technique with a KrF excimer laser (λ = 248 nm). The sp3 content in the films varied between 20% and 42% by changing the laser energy density. Subsequently, PLA was performed on the DLC films by using the KrF excimer laser with energy densities between 0.5 and 1.2 J/cm2. The prepared films were characterized using scanning electron microscopy, Raman spectroscopy, and magnetization measurements. Consequently, for the combination of 20% sp3 content and laser density of 1.0 J/cm2, as well as 42% sp3 and 0.5 J/cm2, the films showed the characteristic features of Q-carbon: filamentary nanostructures, the presence of a T band in the Raman spectrum, room-temperature ferromagnetic behavior, and ∼80% sp3 content. The results indicate that Q-carbon can be obtained by using a proper combination of sp3 content in DLC films and an appropriate PLA energy density. This study provides important guidance for establishing a preparation method for Q-carbon.
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- 2020
11. Data-driven exploration for pressure-induced superconductors using diamond anvil cell with boron-doped diamond electrodes and undoped diamond insulating layer
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Zhufeng Hou, Kensei Terashima, Yoshihiko Takano, Hiroyuki Takeya, Tetsuo Irifune, Ryo Matsumoto, Sayaka Yamamoto, Kiyoyuki Terakura, Takayoshi Yokoya, Pedro Baptista de Castro, Noriyuki Kataoka, Masanori Nagao, Peng Song, Hiromi Tanaka, and Shintaro Adachi
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Superconductivity ,Boron doped diamond ,Materials science ,business.industry ,Electronic band ,Diamond ,engineering.material ,010502 geochemistry & geophysics ,Condensed Matter Physics ,01 natural sciences ,Diamond anvil cell ,0103 physical sciences ,Electrode ,engineering ,Optoelectronics ,010306 general physics ,business ,Layer (electronics) ,0105 earth and related environmental sciences - Abstract
Data-driven exploration for pressure-induced superconductors was performed based on the high-throughput first-principles screening of electronic band structures. In the screening conditions, we foc...
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- 2019
12. Modification of the synthesis of layered titanium chloride nitride
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Masashi Tanaka, Noriyuki Kataoka, Haruya Kobayashi, Masaya Fujioka, Masaru Oda, Aishi Yamamoto, Kensei Terashima, Junji Nishii, Hiromi Tanaka, and Takayoshi Yokoya
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Mechanics of Materials ,Mechanical Engineering ,General Materials Science ,Condensed Matter Physics - Published
- 2022
13. Selective Reduction Mechanism of Graphene Oxide Driven by the Photon Mode versus the Thermal Mode
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Ken Onda, Chihiro Itoh, Shin-ya Koshihara, Satoshi Ohmura, Ikufumi Katayama, Yusuke Arashida, Kiyoshi Miyata, Takayoshi Yokoya, Masaki Hada, Shota Mizote, Jun Takeda, Wang Chen, Yasuhiko Hayashi, Ryo Fukaya, Tomoharu Tokunaga, Kenji Tsuruta, Takayuki Suzuki, Yuta Nishina, Kohei Ichiyanagi, Takayoshi Sawa, Shin-ichi Adachi, Toshio Seki, Jiro Matsuo, and Shunsuke Nozawa
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Materials science ,Photon ,business.industry ,Graphene ,General Engineering ,Oxide ,General Physics and Astronomy ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,law.invention ,chemistry.chemical_compound ,chemistry ,law ,Thermal ,Optoelectronics ,General Materials Science ,Selective reduction ,0210 nano-technology ,business - Abstract
A two-dimensional nanocarbon, graphene, has attracted substantial interest due to its excellent properties. The reduction of graphene oxide (GO) has been investigated for the mass production of gra...
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- 2019
14. Asymmetric Phosphorus Incorporation in Homoepitaxial P-Doped (111) Diamond Revealed by Photoelectron Holography
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Takanori Wakita, Takayuki Muro, Takayoshi Yokoya, Satoshi Yamasaki, Yuji Muraoka, Hiromitsu Kato, Toyohiko Kinoshita, Aya Takeda, Hirokazu Fujiwara, Tetsushi Fukura, Tomohiro Matsushita, Tamio Oguchi, and Kensei Terashima
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Materials science ,substitutional doping ,Bioengineering ,02 engineering and technology ,Chemical vapor deposition ,engineering.material ,dopant-vacancy complex ,Crystal ,diamond ,Vacancy defect ,General Materials Science ,Diamond cubic ,Dopant local structure ,Dopant ,Mechanical Engineering ,Resolution (electron density) ,Doping ,Diamond ,General Chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,photoelectron holography ,Chemical physics ,engineering ,asymmetric dopant incorporation ,0210 nano-technology - Abstract
Diamond has two crystallographically inequivalent sites in the unit cell. In doped diamond, dopant occupation in the two sites is expected to be equal. Nevertheless, preferential dopant occupation during growth under nonequilibrium conditions is of fundamental importance, for example, to enhance the properties of nitrogen-vacancy (N-V) centers; therefore, this is a promising candidate for a qubit. However, the lack of suitable experimental techniques has made it difficult to study the crystal- and chemical-site-resolved local structures of dopants. Here, we confirm the identity of two chemical sites with asymmetric dopant incorporation in the diamond structure, via the photoelectron holography (PEH) of heavily phosphorus (P)-doped diamond prepared by chemical vapor deposition. One is substitutionally incorporated P with preferential site occupations and the other can be attributed to a PV split vacancy complex with preferential orientation. The present study shows that PEH is a valuable technique to study the local structures around dopants with a resolution of crystallographically inequivalent but energetically equivalent sites/orientations. Such information provides strategies to improve the properties of dopant related-complexes in which alignment is crucial for sensing of magnetic field or quantum spin register using N-V centers in diamond.
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- 2019
15. Strain relaxation and spinodal decomposition in composition adjusted TiO2-VO2 films on TiO2(100) substrates
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Takahiro Fukuda, Yoshito Takemoto, Takanori Wakita, Takayoshi Yokoya, and Yuji Muraoka
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Materials Chemistry ,Metals and Alloys ,Surfaces and Interfaces ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials - Published
- 2022
16. Multilayer formation via spinodal decomposition in TiO2-VO2 epitaxial films on sapphire substrates
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Yuka Matsuura, Takanori Wakita, Tsubasa Otsuka, Masataka Ijiri, Kensei Terashima, Takayoshi Yokoya, Yoshito Takemoto, Fumiya Yoshii, Yuji Muraoka, and K. Kadowaki
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010302 applied physics ,Spinodal ,Materials science ,Condensed matter physics ,Spinodal decomposition ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Epitaxy ,01 natural sciences ,Pulsed laser deposition ,Phase (matter) ,0103 physical sciences ,Scanning transmission electron microscopy ,Materials Chemistry ,Ceramics and Composites ,Sapphire ,Lamellar structure ,0210 nano-technology - Abstract
We present multilayer formation via spinodal decomposition in rutile TiO2-VO2 (TVO) epitaxial films on sapphire substrates. (001)- and (101)-oriented TVO solid-solution films are grown epitaxially on TiO2/Al2O3 using a pulsed laser deposition technique and annealed inside the spinodal region. X-ray diffraction measurements and scanning transmission electron microscopy (STEM) observations show that the films are phase-separated along the [001] direction and lamellar structures are formed in a parallel or slanted direction to the sapphire substrates depending on the film orientation. The results indicate the multilayer formation via spinodal decomposition in the TVO films. STEM investigations also reveal a relatively high Ti concentration in the decomposed phases, reflecting the influence of lattice deformation on the phase decomposition in the films. Our work shows that spinodal decomposition is a promising approach for the formation of a multilayer structure in TVO films and helps deepen understanding the spinodal decomposition in TVO system.
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- 2018
17. Fermi surface topology in a metallic phase of VO2 thin films grown on TiO2(001) substrates
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Yuji Muraoka, Hiroki Nagao, Yuichiro Yao, Kensei Terashima, Hiroshi Kumigashira, Takayoshi Yokoya, Masaharu Oshima, and Takanori Wakita
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Multidisciplinary ,Materials science ,Photoemission spectroscopy ,Peierls transition ,lcsh:R ,Synchrotron radiation ,lcsh:Medicine ,Angle-resolved photoemission spectroscopy ,Fermi surface ,Electron ,Topology ,01 natural sciences ,Article ,010305 fluids & plasmas ,Phase (matter) ,0103 physical sciences ,Condensed Matter::Strongly Correlated Electrons ,lcsh:Q ,010306 general physics ,Electronic band structure ,lcsh:Science - Abstract
Since the first observation of the metal-to-insulator transition (MIT), VO2 has attracted substantial attention in terms of whether this transition is impelled by electron–phonon interaction (Peierls transition) or electron–electron interaction. Regarding Peierls transition, it has been theoretically predicted that the Fermi surface (FS) cross-section exhibits certain nesting features for a metallic phase of VO2. Various experimental studies related to the nesting feature have been reported. Nevertheless, there is no experimental result on FS topology. In this work, we determine the FS topology of the metallic phase of VO2 through studies of VO2 epitaxial thin films on TiO2(001) substrates, using synchrotron radiation angle-resolved photoemission spectroscopy (ARPES). Three electron pockets around Γ are observed in band structures along the Γ–X direction. These three bands form electron surfaces around Γ in the ΓXRZ plane. Furthermore, the lowest energy band FS exhibits the nesting feature corresponding to a nesting vector $$\overrightarrow{q}$$ q → = ΓR, as predicted by the calculation. Our results strongly indicate the formation of the charge-density wave with $$\overrightarrow{q}$$ q → = ΓR and thus, the importance of Peierls transition for the mechanism of the MIT in VO2.
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- 2018
18. Temperature dependent local atomic displacements in ammonia intercalated iron selenide superconductor
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Wojciech Olszewski, Laura Simonelli, Eugenio Paris, Takumi Kimura, Naoki Nishimoto, Takeshi Kakuto, Ji Hyun Lee, Naurang L. Saini, Kazutaka Kudo, Takashi Kambe, Takanori Wakita, Kensei Terashima, Minoru Nohara, Carlo Marini, and Takayoshi Yokoya
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Superconductivity ,Multidisciplinary ,Materials science ,Condensed matter physics ,Extended X-ray absorption fine structure ,molecular intercalation ,superconductors ,Intercalation (chemistry) ,Mineralogy ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Article ,chemistry.chemical_compound ,chemistry ,Lattice (order) ,Selenide ,Condensed Matter::Superconductivity ,0103 physical sciences ,Hardening (metallurgy) ,Tetrahedron ,Cuprate ,010306 general physics ,0210 nano-technology - Abstract
Recently, ammonia-thermal reaction has been used for molecular intercalation in layered FeSe, resulting a new Lix(NH3)yFe2Se2 superconductor with Tc ~ 45 K. Here, we have used temperature dependent extended x-ray absorption fine structure (EXAFS) to investigate local atomic displacements in single crystals of this new superconductor. Using polarized EXAFS at Fe K-edge we have obtained direct information on the local Fe-Se and Fe-Fe bondlengths and corresponding mean square relative displacements (MSRD). We find that the Se-height in the intercalated system is lower than the one in the binary FeSe, suggesting compressed FeSe4 tetrahedron in the title system. Incidentally, there is hardly any effect of the intercalation on the bondlengths characteristics, revealed by the Einstein temperatures, that are similar to those found in the binary FeSe. Therefore, the molecular intercalation induces an effective compression and decouples the FeSe slabs. Furthermore, the results reveal an anomalous change in the atomic correlations across Tc, appearing as a clear decrease in the MSRD, indicating hardening of the local lattice mode. Similar response of the local lattice has been found in other families of superconductors, e.g., A15-type and cuprates superconductors. This observation suggests that local atomic correlations should have some direct correlation with the superconductivity.
- Published
- 2021
19. Soft x-ray irradiation induced metallization of layered TiNCl
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Takanori Wakita, Noriyuki Kataoka, Yuji Muraoka, Takayoshi Yokoya, Wataru Hosoda, Masashi Tanaka, Takumi Taniguchi, and Shin-ichi Fujimori
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Materials science ,Photoemission spectroscopy ,Analytical chemistry ,FOS: Physical sciences ,02 engineering and technology ,01 natural sciences ,symbols.namesake ,Condensed Matter - Strongly Correlated Electrons ,Desorption ,0103 physical sciences ,General Materials Science ,Irradiation ,010306 general physics ,Spectroscopy ,Condensed Matter - Materials Science ,Strongly Correlated Electrons (cond-mat.str-el) ,Doping ,Fermi level ,Resonance ,Materials Science (cond-mat.mtrl-sci) ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Chemical state ,symbols ,0210 nano-technology - Abstract
We have performed soft x-ray spectroscopy in order to study the photoirradiation time dependence of the valence band structure and chemical states of layered transition metal nitride chloride TiNCl. Under the soft x-ray irradiation, the intensities of the states near the Fermi level (E F) and the Ti3+ component increased, while the Cl 2p intensity decreased. Ti 2p–3d resonance photoemission spectroscopy confirmed a distinctive Fermi edge with Ti 3d character. These results indicate the photo-induced metallization originates from deintercalation due to Cl desorption, and thus provide a new carrier doping method that controls the conducting properties of TiNCl.
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- 2020
20. High-pressure x-ray absorption and diffraction study of the self-doped superconductor EuFBiS2
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Takayoshi Yokoya, Naurang L. Saini, Takashi Mizokawa, Eugenio Paris, Kensei Terashima, Takanori Wakita, Carlo Marini, Yoshikazu Mizuguchi, and Boby Joseph
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Superconductivity ,Physics ,Valence (chemistry) ,Absorption spectroscopy ,Condensed matter physics ,mixed valence ,Charge (physics) ,Ion ,high pressure ,Tetragonal crystal system ,self doping ,local structure ,Condensed Matter::Strongly Correlated Electrons ,Charge carrier ,Absorption (logic) - Abstract
The ${\mathrm{BiS}}_{2}$-based layered materials are characterized by a highly susceptible physical state, revealing a large response to external conditions. A particular case is the ${\mathrm{EuFBiS}}_{2}$ compound, showing a superconducting transition temperature ${T}_{c}\ensuremath{\sim}0.3$ K at ambient pressure. Upon increasing external pressure, ${T}_{c}$ goes through a large amplification, accompanied by a structural phase transition (SPT) from tetragonal to monoclinic symmetry. Here, we use a combination of Eu ${\phantom{\rule{4pt}{0ex}}L}_{3}$ - edge x-ray absorption spectroscopy and synchrotron x-ray diffraction to unveil the evolution of the Eu valence and lattice symmetry under high pressure. We find that the average Eu valence increases gradually with pressure, exhibiting a pressure plateau near the SPT, at which the ${T}_{c}$ increases sharply. Since in ${\mathrm{EuFBiS}}_{2}$ the charge carriers are introduced via self-doping induced by the mixed valence of the Eu ions, our findings clearly indicate that the role of the charge doping is marginal in the ${T}_{c}$ enhancement. On the other hand, the structural distortions, taking place at the SPT, play a central role in enhancing the superconducting properties of the ${\mathrm{EuFBiS}}_{2}$ system.
- Published
- 2020
21. Change in the Work Function of VO2 Thin Film Across the Metal–Insulator Transition in VO2/TiO2:Nb(001) Heterostructures
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Hayato Nakahara, Yuji Muraoka, Takayoshi Yokoya, and Yuki Suga
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Materials science ,business.industry ,Optoelectronics ,Heterojunction ,Work function ,Metal–insulator transition ,Thin film ,business - Published
- 2020
22. Skewed electronic band structure induced by electric polarization in ferroelectric BaTiO
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Norihiro, Oshime, Jun, Kano, Eiji, Ikenaga, Shintaro, Yasui, Yosuke, Hamasaki, Sou, Yasuhara, Satoshi, Hinokuma, Naoshi, Ikeda, Pierre-Eymeric, Janolin, Jean-Michel, Kiat, Mitsuru, Itoh, Takayoshi, Yokoya, Tatsuo, Fujii, Akira, Yasui, and Hitoshi, Osawa
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Ferroelectrics and multiferroics ,Condensed Matter::Materials Science ,Article - Abstract
Skewed band structures have been empirically described in ferroelectric materials to explain the functioning of recently developed ferroelectric tunneling junction (FTJs). Nonvolatile ferroelectric random access memory (FeRAM) and the artificial neural network device based on the FTJ system are rapidly developing. However, because the actual ferroelectric band structure has not been elucidated, precise designing of devices has to be advanced through appropriate heuristics. Here, we perform angle-resolved hard X-ray photoemission spectroscopy of ferroelectric BaTiO3 thin films for the direct observation of ferroelectric band skewing structure as the depth profiles of atomic orbitals. The depth-resolved electronic band structure consists of three depth regions: a potential slope along the electric polarization in the core, the surface and interface exhibiting slight changes. We also demonstrate that the direction of the energy shift is controlled by the polarization reversal. In the ferroelectric skewed band structure, we found that the difference in energy shifts of the atomic orbitals is correlated with the atomic configuration of the soft phonon mode reflecting the Born effective charges. These findings lead to a better understanding of the origin of electric polarization.
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- 2020
23. Change in the electronic structure of the bismuth chalcogenide superconductor CsBi
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Hiroyuki, Okazaki, Kensei, Terashima, David, Billington, Keiji, Iwata, Takanori, Wakita, Masashi, Tanaka, Yoshihiko, Takano, Yuji, Muraoka, and Takayoshi, Yokoya
- Abstract
CsBi
- Published
- 2019
24. Metallic phase in stoichiometric CeOBiS2 revealed by space-resolved ARPES
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Eugenio Paris, Ryuji Higashinaka, Joe Kajitani, Takayoshi Yokoya, Naurang L. Saini, Alexei Barinov, Takanori Wakita, Yuji Aoki, Tatsuma D. Matsuda, T. Sugimoto, Takashi Mizokawa, and Kensei Terashima
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Superconductivity ,Materials science ,Multidisciplinary ,Condensed matter physics ,Doping ,lcsh:R ,lcsh:Medicine ,Angle-resolved photoemission spectroscopy ,Fermi surface ,02 engineering and technology ,Electron ,021001 nanoscience & nanotechnology ,01 natural sciences ,Instability ,Metal ,visual_art ,Phase (matter) ,Condensed Matter::Superconductivity ,0103 physical sciences ,visual_art.visual_art_medium ,Condensed Matter::Strongly Correlated Electrons ,lcsh:Q ,010306 general physics ,0210 nano-technology ,lcsh:Science - Abstract
Recently CeOBiS2 system without any fluorine doping is found to show superconductivity posing question on its origin. Using space resolved ARPES we have found a metallic phase embedded in the morphological defects and at the sample edges of stoichiometric CeOBiS2. While bulk of the sample is semiconducting, the embedded metallic phase is characterized by the usual electron pocket at X point, similar to the Fermi surface of doped BiS2-based superconductors. Typical size of the observed metallic domain is larger than the superconducting correlation length of the system suggesting that the observed superconductivity in undoped CeOBiS2 might be due to this embedded metallic phase at the defects. The results also suggest a possible way to develop new systems by manipulation of the defects in these chalcogenides with structural instability.
- Published
- 2018
25. Observation of intrinsic half-metallic behavior of CrO2 (100) epitaxial films by bulk-sensitive spin-resolved PES
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Masanori Sunagawa, Yuji Muraoka, Hirokazu Fujiwara, Kensei Terashima, Takanori Wakita, Takayoshi Yokoya, and Tomoko Kittaka
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Photoemission spectroscopy ,FOS: Physical sciences ,02 engineering and technology ,Epitaxy ,01 natural sciences ,Condensed Matter - Strongly Correlated Electrons ,symbols.namesake ,Magnetization ,0103 physical sciences ,Physical and Theoretical Chemistry ,010306 general physics ,Spectroscopy ,Spin-½ ,Physics ,Radiation ,Strongly Correlated Electrons (cond-mat.str-el) ,Spintronics ,Condensed matter physics ,Spin polarization ,Fermi level ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Ferromagnetism ,symbols ,Condensed Matter::Strongly Correlated Electrons ,0210 nano-technology - Abstract
We have investigated the electronic states and spin polarization of half-metallic ferromagnet CrO$_2$ (100) epitaxial films by bulk-sensitive spin-resolved photoemission spectroscopy with a focus on non-quasiparticle (NQP) states derived from electron-magnon interactions. We found that the averaged values of the spin polarization are approximately 100% and 40% at 40 K and 300 K, respectively. This is consistent with the previously reported result [H. Fujiwara et al., Appl. Phys. Lett. 106, 202404 (2015).]. At 100 K, peculiar spin depolarization was observed at the Fermi level ($E_{F}$), which is supported by theoretical calculations predicting NQP states. This suggests the possible appearance of NQP states in CrO$_2$. We also compare the temperature dependence of our spin polarizations with that of the magnetization., Comment: 8 pages, 3 figures, VUVX 2016
- Published
- 2017
26. Photoinduced oxygen transport in cobalt double-perovskite crystal EuBaCo2O5.39
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Fuyuki Shimojo, Kenji Tsuruta, Wataru Yajima, Takayoshi Yokoya, Ken Onda, Yusuke Masaki, Nobuyuki Abe, Masaki Hada, Daisuke Urushihara, Makoto Kuwahara, Taka-hisa Arima, Toru Asaka, Naoya Keio, Satoshi Ohmura, Tadahiko Ishikawa, Masaki Saigo, Yasuhiko Hayashi, Muneaki Hase, Yoichi Okimoto, Shin-ya Koshihara, Jiro Matsuo, Kou Takubo, Tatsuya Suzuki, and Sumio Ishihara
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Materials science ,Oxide ,Oxygen transport ,Ionic bonding ,Ion ,Photoexcitation ,Crystal ,Condensed Matter::Materials Science ,chemistry.chemical_compound ,chemistry ,Chemical physics ,Proton transport ,General Materials Science ,Strongly correlated material ,Physics::Chemical Physics - Abstract
Understanding and controlling atomic motions in solid are essential in ionic materials, such as ion conductors, electrolyte and electrodes of batteries, and gas separators. Although photoinduced proton transport in solid materials has been demonstrated, photoinduced transport of heavier ions, such as the oxide ion, in solid materials remains entirely elusive. Herein, we apply ultrafast time-resolved electron diffraction to observe the large displacement of oxide ions in a strongly correlated material, EuBaCo2O5.39, under near-ultraviolet photoexcitation at room temperature. The mechanism of the photoinduced transport of oxide ions is revealed via the combination of ultrafast optical spectroscopy and density functional theory calculations. Our findings show that photoexcitation induces ionic motions in a ceramic crystal at room temperature through the charge transfer that strongly couples with large ionic displacement under the nonequilibrium condition.
- Published
- 2021
27. Effect of aliovalent dopants on the kinetics of spinodal decomposition in rutile-type TiO 2 -VO 2
- Author
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Takayoshi Yokoya, Yuji Muraoka, K. Kadowaki, Makoto Ogata, Takanori Wakita, Yoshito Takemoto, Kensei Terashima, and Masataka Ijiri
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010302 applied physics ,Spinodal ,Materials science ,Dopant ,Spinodal decomposition ,Inorganic chemistry ,Doping ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Chemical physics ,Vacancy defect ,Phase (matter) ,0103 physical sciences ,Materials Chemistry ,Ceramics and Composites ,Lamellar structure ,Crystallite ,0210 nano-technology - Abstract
The effects of aliovalent dopants on the kinetics of spinodal decomposition in a rutile-type TiO2-VO2 system were studied by means of x-ray diffraction and transmission electron microscopy. In this study, as-prepared polycrystalline samples were annealed at 673 k inside the spinodal. For undoped samples, phase decomposition occurred along the [001] direction, and a lamellar structure formed on the nanometer length scale. The phase decomposition kinetics in this system were sensitive to the type of aliovalent dopant; the decomposition rate in a sample doped with Al2O3 was more than one order of magnitude higher than a sample doped with Nb2O5. These observations could be explained on the basis of the premise that cation interstitial mobility is greater than cation vacancy mobility. The obtained results are consistent with those for a TiO2-SnO2 system, indicating that phase separation in both rutile-type oxide systems can be interpreted through a common framework.
- Published
- 2017
28. The electronic structure of Ag1−xSn1+xSe2 (x = 0.0, 0.1, 0.2, 0.25 and 1.0)
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Igor Píš, Kaya Kobayashi, Yuji Muraoka, Takanori Wakita, Kensei Terashima, Muammer Yasin Hacisalihoǧlu, Teppei Ueno, Federica Bondino, Eugenio Paris, Elena Magnano, Naurang L. Saini, Luca Olivi, Takayoshi Yokoya, and Jun Akimitsu
- Subjects
combined analysis ,010302 applied physics ,X-ray absorption spectroscopy ,Valence (chemistry) ,Absorption spectroscopy ,Photoemission spectroscopy ,Chemistry ,Analytical chemistry ,General Physics and Astronomy ,Electron ,Electronic structure ,01 natural sciences ,Spectral line ,Physics and Astronomy (all) ,X-ray photoelectron spectroscopy ,Physical and Theoretical Chemistry ,0103 physical sciences ,010306 general physics - Abstract
We have studied the valence electronic structure of Ag1-xSn1+xSe2 (x = 0.0, 0.1, 0.2, 0.25) and SnSe (x = 1.0) by a combined analysis of X-ray absorption spectroscopy (XAS) and X-ray photoemission spectroscopy (XPS) measurements. Both XAS and XPS reveal an increase in electron carriers in the system with x (i.e. excess Sn concentration) for 0 ≤ x ≤ 0.25. The core-level spectra (Sn 3d, Ag 3d and Se 3d) show that the charge state of Ag is almost 1+, while that of of Sn splits into Sn2+ and Sn4+ (providing clear evidence of valence skipping for the first time) with a concomitant splitting of Se into Se2- and Se2-δ states. The x dependence of the split components in Sn and Se together with the Se-K edge XAS reveals that the Se valence state may have an essential role in the transport properties of this system.
- Published
- 2017
29. Pressure-induced superconductivity in Bi2−xSbxTe3−ySey
- Author
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Tong He, Kensei Terashima, Kaya Kobayashi, Jun Akimitsu, Xiaofan Yang, Teppei Ueno, Harald Olaf Jeschke, Yoshihiro Kubozono, Hirofumi Ishii, Yen Fa Liao, Hidenori Goto, Ritsuko Eguchi, Takayoshi Yokoya, Hitoshi Yamaoka, Xianxin Wu, Hiromi Ota, and Tomoya Taguchi
- Subjects
Physics ,Superconductivity ,Structural phase ,02 engineering and technology ,Crystal structure ,Trigonal crystal system ,Pressure dependence ,021001 nanoscience & nanotechnology ,01 natural sciences ,Pressure range ,Crystallography ,Electrical transport ,0103 physical sciences ,010306 general physics ,0210 nano-technology ,Monoclinic crystal system - Abstract
We systematically investigated the pressure dependence of electrical transport and the crystal structure of topological insulator, $\mathrm{B}{\mathrm{i}}_{2\ensuremath{-}x}\mathrm{S}{\mathrm{b}}_{x}\mathrm{T}{\mathrm{e}}_{3\ensuremath{-}y}\mathrm{S}{\mathrm{e}}_{y}$, which showed no superconductivity down to 2.0 K at ambient pressure. The $\mathrm{B}{\mathrm{i}}_{2\ensuremath{-}x}\mathrm{S}{\mathrm{b}}_{x}\mathrm{T}{\mathrm{e}}_{3\ensuremath{-}y}\mathrm{S}{\mathrm{e}}_{y}$ crystal showed two structural phase transitions under pressure, from rhombohedral structure (space group No. 166, $R\overline{3}m$, termed phase I) to monoclinic structure (space group No. 12, $C2/m$, termed phase II), and from phase II to another monoclinic structure (space group No. 12, $C2/m$, termed phase III). Superconductivity appeared when applying pressure; actually the superconductivity of all $\mathrm{B}{\mathrm{i}}_{2\ensuremath{-}x}\mathrm{S}{\mathrm{b}}_{x}\mathrm{T}{\mathrm{e}}_{3\ensuremath{-}y}\mathrm{S}{\mathrm{e}}_{y}$ samples emerged in phase I. The superconducting transition temperature, ${T}_{\mathrm{c}}$, increased against pressure in a pressure range of 0--15 GPa for all $\mathrm{B}{\mathrm{i}}_{2\ensuremath{-}x}\mathrm{S}{\mathrm{b}}_{x}\mathrm{T}{\mathrm{e}}_{3\ensuremath{-}y}\mathrm{S}{\mathrm{e}}_{y}$ samples, and the maximum ${T}_{\mathrm{c}}$ was 5.45 K, recorded at 13.5 GPa in $\mathrm{B}{\mathrm{i}}_{2\ensuremath{-}x}\mathrm{S}{\mathrm{b}}_{x}\mathrm{T}{\mathrm{e}}_{3\ensuremath{-}y}\mathrm{S}{\mathrm{e}}_{y}$ at $x=0$ and $y=1.0$. The magnetic field (H) dependence of the R--T plot for $\mathrm{B}{\mathrm{i}}_{2\ensuremath{-}x}\mathrm{S}{\mathrm{b}}_{x}\mathrm{T}{\mathrm{e}}_{3\ensuremath{-}y}\mathrm{S}{\mathrm{e}}_{y}$ was measured to characterize the superconducting pairing mechanism of pressure-induced superconducting phase.
- Published
- 2019
30. Selective Reduction Mechanism of Graphene Oxide Driven by the Photon Mode
- Author
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Masaki, Hada, Kiyoshi, Miyata, Satoshi, Ohmura, Yusuke, Arashida, Kohei, Ichiyanagi, Ikufumi, Katayama, Takayuki, Suzuki, Wang, Chen, Shota, Mizote, Takayoshi, Sawa, Takayoshi, Yokoya, Toshio, Seki, Jiro, Matsuo, Tomoharu, Tokunaga, Chihiro, Itoh, Kenji, Tsuruta, Ryo, Fukaya, Shunsuke, Nozawa, Shin-Ichi, Adachi, Jun, Takeda, Ken, Onda, Shin-Ya, Koshihara, Yasuhiko, Hayashi, and Yuta, Nishina
- Abstract
A two-dimensional nanocarbon, graphene, has attracted substantial interest due to its excellent properties. The reduction of graphene oxide (GO) has been investigated for the mass production of graphene used in practical applications. Different reduction processes produce different properties in graphene, affecting the performance of the final materials or devices. Therefore, an understanding of the mechanisms of GO reduction is important for controlling the properties of functional two-dimensional systems. Here, we determined the average structure of reduced GO prepared
- Published
- 2019
31. Three-dimensional dopant imaging in semiconductor crystals using photoelectron holography with chemical state identification
- Author
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Kazuo Tsutsui, Takayoshi Yokoya, Tomohiro Matsushita, and Takayuki Muro
- Subjects
Materials science ,Dopant ,business.industry ,Doping ,Holography ,Semiconductor device ,Iterative reconstruction ,law.invention ,Chemical state ,Semiconductor ,law ,Optoelectronics ,Neutron ,business - Abstract
Doping is an important technology for modern science. For example, to create a semiconductor device, a circuit is formed by controlling carriers by doping. It is important to search for appropriate conditions since the carrier emission from dopant differs depending on the doping conditions. The atomic arrangement around the dopant differs depending on the conditions. Therefore, it has been desired to observe the atomic arrangement around the dopant, but it has been difficult with conventional measurement methods. The atomic resolution holography such as photoelectron holography, x-ray fluorescence holography, neutron holography, which are methods that can measure the three-dimensional (3D) atomic arrangement of the dopant. Among them, photoelectron holography can measure the atomic structure of each dopant depending on the chemical state. We have built photoelectron holography apparatuses at BL25SU in SPring-8. We also developed a software platform 3D-AIR-IMAGE for data processing, simulation of photoelectron holograms, and 3D atomic image reconstruction.
- Published
- 2019
32. ��-PES Studies on TiNCl and Quasi-two-dimensional Superconductor Na-intercalated TiNCl
- Author
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Yuji Muraoka, Noriyuki Kataoka, Takayoshi Yokoya, Takanori Wakita, Takumi Taniguchi, Wataru Hosoda, Kensei Terashima, and Masashi Tanaka
- Subjects
Superconductivity ,Materials science ,Condensed matter physics ,Electronic correlation ,Condensed Matter - Superconductivity ,Fermi level ,General Physics and Astronomy ,FOS: Physical sciences ,Rigid-band model ,Electron ,Electronic structure ,01 natural sciences ,Spectral line ,010305 fluids & plasmas ,Superconductivity (cond-mat.supr-con) ,symbols.namesake ,0103 physical sciences ,symbols ,010306 general physics ,Spectroscopy - Abstract
Electron-doped TiNCl is a superconductor, for which exotic mechanisms of the superconductivity have been discussed. However, difficulty in preparing large single-phase samples has prevented the direct observation of its electronic structure and how that changes with electron doping. In this study, micro-photoemission spectroscopy ({\mu}-PES) was used to reveal the electronic structures of TiNCl and Na-intercalated TiNCl (Na-TiNCl). Comparison of Ti 2p core-level spectra shows the enhancement of a spectral feature in Na-TiNCl that suggests an increase in its metallic character. This indicates the introduction of electron carriers to the TiNCl layers. Although the overall valence band electronic structure of parent TiNCl could be reproduced by first-principle calculations, that of Na-TiNCl showed a marked deviation from the rigid band model near the Fermi level (EF). The spectral shape observed near EF of Na-TiNCl was found to be similar to a result in early transition metal oxides that has been attributed to the effect of strong electron correlation. The present study also demonstrated the usefulness of {\mu}-PES to obtain reliable electronic structure data for samples that are difficult to make at large sizes., Comment: 14 page, 5 figures
- Published
- 2019
- Full Text
- View/download PDF
33. Physics of Heavily Doped Diamond: Electronic States and Superconductivity
- Author
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Takanori Wakita, Takayoshi Yokoya, and Kensei Terashima
- Subjects
Superconductivity ,Physics ,Condensed matter physics ,Photoemission spectroscopy ,Doping ,chemistry.chemical_element ,Diamond ,engineering.material ,Atomic mass ,Electronic states ,Condensed Matter::Materials Science ,chemistry ,Covalent bond ,Condensed Matter::Superconductivity ,engineering ,Carbon - Abstract
Diamond is a popular material, not only as a gem but also for basic and applied research owing to its extraordinary properties. The discovery of superconductivity in heavily doped diamond has increased its importance. Although the highest superconducting critical temperature (Tc) is 10 K, it is regarded as a superconductor with a potentially high Tc, owing to the strong covalent bonding between carbon atoms and the light atomic mass of carbon. In this chapter, after reviewing the fundamentals of the electronic states of pristine and doped diamond, we describe the electronic states, together with the vibrational properties, of boron-doped superconductive diamond, which have been revealed by photoemission spectroscopy and other experimental techniques.
- Published
- 2019
34. Enhanced thermoelectricity by controlled local structure in bismuth-chalcogenides
- Author
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Yuji Muraoka, Eugenio Paris, Yosuke Goto, Yuko Yano, Naurang L. Saini, Takanori Wakita, Kensei Terashima, Yoichi Kamihara, Takayoshi Yokoya, and Yoshikazu Mizuguchi
- Subjects
Physics and Astronomy (all) ,spectroscopy ,spectroscopic techniques ,Electron mobility ,Materials science ,General Physics and Astronomy ,chemistry.chemical_element ,FOS: Physical sciences ,02 engineering and technology ,Electronic structure ,Crystal structure ,01 natural sciences ,Bismuth ,X-ray photoelectron spectroscopy ,0103 physical sciences ,Thermoelectric effect ,Absorption (electromagnetic radiation) ,010302 applied physics ,Condensed Matter - Materials Science ,Materials Science (cond-mat.mtrl-sci) ,021001 nanoscience & nanotechnology ,Thermoelectric materials ,chemistry ,Chemical physics ,0210 nano-technology - Abstract
Spectroscopic techniques, including photoelectron spectroscopy, diffuse reflectance, and x-ray absorption, are used to investigate the electronic structure and the local structure of LaOBiS$_{2-x}$Se$_x$ thermoelectric material. It is found that Se substitution effectively suppresses local distortion, that can be responsible for the increased carrier mobility together with a change in the electronic structure. The results suggest a possible way to control thermoelectric properties by tuning of the local crystal structure of these materials., Comment: 6 pages, 4 figures, 1 table, J. Appl. Phys. (in press)
- Published
- 2019
- Full Text
- View/download PDF
35. Inhomogeneous charge distribution in a self-doped EuFBiS2 superconductor
- Author
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Kensei Terashima, Takashi Mizokawa, Takanori Wakita, Eugenio Paris, Ryuji Higashinaka, Alessio Giampietri, Joe Kajitani, T. Sugimoto, Tatsuma D. Matsuda, Takayoshi Yokoya, Y. Aoki, A. Barinov, and Naurang L. Saini
- Subjects
Superconductivity ,Mesoscopic physics ,Valence (chemistry) ,Materials science ,BiS2-based superconductors ,Condensed matter physics ,self-doping ,Doping ,Charge density ,Fermi surface ,electronic structure ,space resolved ARPES ,Condensed Matter::Superconductivity ,BiS2-based superconductors, self-doping, space resolved ARPES, electronic structure ,Condensed Matter::Strongly Correlated Electrons ,Density functional theory ,Stoichiometry - Abstract
Stoichiometric ${\mathrm{EuFBiS}}_{2}$ with mixed valent Eu shows self-doped superconductivity at low temperatures due to the Eu-to-Bi charge transfer. The metallic/nonmetallic bistability of the ${\mathrm{BiS}}_{2}$ layer can couple with the valence fluctuation of Eu and provide a highly susceptible electronic state. Here, we report space-resolved photoemission measurements on ${\mathrm{EuFBiS}}_{2}$ revealing an inhomogeneous charge distribution with the coexistence of metallic and nonmetallic phases at mesoscopic length scales. Angle-resolved photoemission measurements using a submicron beam size have confirmed a clear Fermi surface around the zone boundaries in the metallic region, typically observed in a doped system, while it can be hardly seen in the nonmetallic region. Density functional theory calculations suggest that the out-of-plane S atom position in the structure is one of the important factors for the self-doping in this material.
- Published
- 2019
36. Temperature dependent local atomic displacements in NaSn2As2 system
- Author
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Naurang L. Saini, G. M. Pugliese, Kensei Terashima, Carlo Marini, Takashi Mizokawa, Yosuke Goto, Takayoshi Yokoya, F. Stramaglia, M. Y. Hacisalihoglu, A. Puri, Laura Simonelli, Yoshikazu Mizuguchi, Hirokazu Fujiwara, and F. D'Acapito
- Subjects
Superconductivity ,layered van der Waals systems ,Materials science ,Condensed matter physics ,superconducting materials ,exfoliable layered materials ,local structure and bond characteristics ,Charge density ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Instability ,symbols.namesake ,Thermal conductivity ,Zintl phase ,Covalent bond ,0103 physical sciences ,symbols ,General Materials Science ,Absorption (chemistry) ,van der Waals force ,010306 general physics ,0210 nano-technology - Abstract
NaSn(2)As(2 )is mechanically exfoliable layered van der Waals (vdW) Zintl phase that is getting interesting due to its low thermal conductivity and recently observed superconductivity. Here, we have investigated the temperature dependent local structure of NaSn2As2 by a combined analysis of As K-edge and Sn K-edge extended x-ray absorption fine structure measurements. The system is intrinsically disordered with the interatomic distances largely consistent to those estimated by average structure measurements. The stretching force constants of different bond distances have been determined using temperature dependent mean square relative displacements. The Sn-As distance is the strongest bond in this system, having covalent nature, unlike the weaker interlayer distances which are characterized by vdW type bonding. Among them, As-Na distance is slightly weaker than Sn-Sn(i) below similar to 200 K and tends to get stronger above this temperature. The anomalous behavior of As-Na bond suggests that the mechanical exfoliation in this system is likely to be temperature dependent. The anomaly in the interlayer atomic correlations may be due to a charge density wave-like instability around this temperature, indicated by earlier experiments. The local structure and disorder are discussed in relation to the physical properties of NaSn2As2.
- Published
- 2019
- Full Text
- View/download PDF
37. Momentum Dependent Band Renormalization and Surface Aging Effect on a Zone Center Electron Pocket in NaSn2As2 Revealed by Angle-Resolved Photoemission Spectroscopy
- Author
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Takashi Mizokawa, Taiki Shimaiwa, Masashi Arita, Takayoshi Yokoya, Yosuke Goto, Naurang L. Saini, Yoshikazu Mizuguchi, Yuka Akabane, Kenya Shimada, Eike F. Schwier, and Shiv Kumar
- Subjects
Physics ,Surface (mathematics) ,Condensed matter physics ,Photoemission spectroscopy ,Astrophysics::High Energy Astrophysical Phenomena ,General Physics and Astronomy ,Fermi surface ,Angle-resolved photoemission spectroscopy ,Electron ,pnictides ,electronic structure ,Momentum ,Renormalization ,ARPE ,Condensed Matter::Strongly Correlated Electrons ,Center (algebra and category theory) - Abstract
We report an angle-resolved photoemission spectroscopy study on NaSn2As2 in which a Sn 5p band is expected to provide interesting Fermi surface geometry with hole-like and electron-like curvatures....
- Published
- 2020
38. Preparation of TaO2 thin films using NbO2 template layers by a pulsed laser deposition technique
- Author
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Kensei Terashima, Takayoshi Yokoya, M. Kameoka, Yuji Muraoka, Takanori Wakita, Masanori Sunagawa, Y. Fujimoto, and Yuka Matsuura
- Subjects
Materials science ,Nanotechnology ,02 engineering and technology ,01 natural sciences ,law.invention ,Pulsed laser deposition ,chemistry.chemical_compound ,X-ray photoelectron spectroscopy ,law ,0103 physical sciences ,Materials Chemistry ,Surface layer ,Thin film ,Crystallization ,010302 applied physics ,Metals and Alloys ,Surfaces and Interfaces ,021001 nanoscience & nanotechnology ,Niobium dioxide ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Amorphous solid ,Surface coating ,Chemical engineering ,chemistry ,0210 nano-technology - Abstract
TaO2 thin films were prepared using rutile-type NbO2 template layers on Al2O3(0001) substrates by a pulsed laser deposition technique. The structural and electronic properties of the films were characterized by performing four-circle X-ray diffraction (XRD) and X-ray photoemission spectroscopy (XPS) measurements. Four-circle XRD measurements revealed the formation and epitaxial growth of (100)-oriented tetragonal TaO2 on the NbO2 template layers. On the other hand, XPS measurements showed two kinds of valence states, namely Ta4 + and Ta5 + in the surface region of the film. The results from the XRD and XPS measurements suggest that the film is composed of epitaxially grown TaO2 with an amorphous Ta2O5 surface layer. It is found from control experiments that the NbO2 template layers play an important role in inducing the crystallization of the TaO2 films and promoting the formation of Ta4 + in the films deposited thereon. The results indicate the effectiveness of the NbO2 template layers for the formation of TaO2 thin films. Our work presents a promising method for the preparation of TaO2 thin films and provides a starting point for further research on TaO2.
- Published
- 2016
39. Theory for High‐Angular‐Resolution Photoelectron Holograms Considering the Inelastic Mean Free Path and the Formation Mechanism of Quasi‐Kikuchi Band
- Author
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Fumihiko Matsui, Kensei Terashima, Takayuki Muro, Takayoshi Yokoya, Yukako Kato, Naoyuki Maejima, Yusuke Hashimoto, Tomohiro Matsushita, and Hirosuke Matsui
- Subjects
Mechanism (engineering) ,Materials science ,law ,engineering ,Holography ,Diamond ,Angular resolution ,engineering.material ,Condensed Matter Physics ,Inelastic mean free path ,Molecular physics ,Electronic, Optical and Magnetic Materials ,law.invention - Published
- 2020
40. Strain effects on spinodal decomposition in TiO2–VO2films on TiO2(100) substrates
- Author
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Kensei Terashima, Yoshito Takemoto, Yuji Muraoka, Takanori Wakita, Yuji Manabe, Takahiro Fukuda, Mikiko Yasuno, Takayoshi Yokoya, and Fumiya Yoshii
- Subjects
Interdiffusion ,Spinodal ,Nanostructure ,Materials science ,Spinodal decomposition ,Thin films ,medicine.medical_treatment ,Pulsed laser deposition ,02 engineering and technology ,01 natural sciences ,0103 physical sciences ,Scanning transmission electron microscopy ,Materials Chemistry ,medicine ,Thin film ,010302 applied physics ,Excimer laser ,Condensed matter physics ,Relaxation (NMR) ,Vanadium dioxide ,Metals and Alloys ,Surfaces and Interfaces ,021001 nanoscience & nanotechnology ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Rutile ,Strain effect ,Titanium dioxide ,0210 nano-technology - Abstract
We investigate the influence of lattice strain in the c-axis direction on spinodal decomposition in rutile TiO2-VO2 films on TiO2(100) substrates. The [100]-oriented Ti0.4V0.6O2 (TVO) solid-solution films are fabricated on rutile TiO2(100) substrates using a pulsed laser deposition with a KrF excimer laser, and are annealed inside the spinodal region. X-ray diffraction and scanning transmission electron microscopy are employed for characterization. Consequently, the in-plane tensile strain in the c-axis direction promotes the Ti-V interdiffusion in TVO/TiO2(100) under thermal annealing. In contrast, relaxation of the tensile strain results in the occurrence of spinodal decomposition along the c-axis direction in the film. These results indicate that the relaxation of the tensile strain in the c-axis direction is critically important for enabling spinodal decomposition in TVO/TiO2(100). Our work helps deepen the understanding of spinodal decomposition in the TVO film and provides information on achieving novel nanostructures via spinodal decomposition in TVO/TiO2(100).
- Published
- 2020
41. Change in the electronic structure of the bismuth chalcogenide superconductor CsBi4−x Pb x Te6 by dissociation of the bismuth dimers
- Author
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Hiroyuki Okazaki, Keiji Iwata, David Billington, Takanori Wakita, Yoshihiko Takano, Masashi Tanaka, Yuji Muraoka, Kensei Terashima, and Takayoshi Yokoya
- Subjects
Superconductivity ,Materials science ,Chalcogenide ,Photoemission spectroscopy ,Doping ,chemistry.chemical_element ,02 engineering and technology ,Electronic structure ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Dissociation (chemistry) ,Bismuth ,chemistry.chemical_compound ,Crystallography ,chemistry ,0103 physical sciences ,General Materials Science ,010306 general physics ,0210 nano-technology ,Electronic band structure - Abstract
CsBi4-x Pb x Te6 is synthesized and the superconductivity associated with the structural transition from Pb substitution is studied. Photoemission spectroscopy measurements are performed in order to elucidate the relationship between the electronic structure and the occurrence of the superconductivity. When Bi is substituted with Pb, an electron doping-like change in the electronic structure is directly observed which is contrary to the naive expectation of hole doping. This observation is consistent with band structure calculations and appears to be a unique characteristic of CsBi4-x Pb x Te6 because of the dissociation of Bi dimers upon Pb substitution. These results indicate that it may be possible to control the electron and hole doping via manipulating the Bi dimers through Pb substitution.
- Published
- 2020
42. Origins of Thermal Spin Depolarization in Half-Metallic Ferromagnet CrO_{2}
- Author
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Fumiya Yoshii, Tetsushi Fukura, Kensei Terashima, Masanori Sunagawa, Yuji Muraoka, Yuko Yano, Makoto Ogata, Shik Shin, Koji Horiba, Takayoshi Yokoya, Hiroshi Kumigashira, Ayumi Harasawa, Yuka Matsuura, Hirokazu Fujiwara, Takanobu Nagayama, Takanori Wakita, Kenta Kuroda, and Koichiro Yaji
- Subjects
Physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Spin states ,Condensed matter physics ,Photoemission spectroscopy ,Demagnetizing field ,Fermi level ,FOS: Physical sciences ,General Physics and Astronomy ,Depolarization ,02 engineering and technology ,Electron ,021001 nanoscience & nanotechnology ,01 natural sciences ,symbols.namesake ,Condensed Matter - Strongly Correlated Electrons ,Ferromagnetism ,0103 physical sciences ,symbols ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology ,Spin-½ - Abstract
Using high-resolution spin-resolved photoemission spectroscopy, we observed a thermal spin depolarization to which all spin-polarized electrons contribute. Furthermore we observed a distinct minority spin state near the Fermi level and a corresponding depolarization that seldom contributes to demagnetization. The origin of this depolarization has been identified as the many-body effect characteristics of half-metallic ferromagnets. Our investigation opens an experimental field of itinerant ferromagnetic physics focusing on phenomena with sub-meV energy scale., 19 pages, 10 figures
- Published
- 2018
43. Temperature-dependent local structure and superconductivity of BaPd2As2 and SrPd2As2
- Author
-
Yasuhiro Yamada, Eugenio Paris, Alessandro Puri, Takayoshi Yokoya, Takanori Wakita, Eduardo Salas-Colera, Laura Simonelli, H. Idei, Minoru Nohara, Seiya Nakano, Kazutaka Kudo, Naurang L. Saini, Yuji Muraoka, Takashi Mizokawa, and Kensei Terashima
- Subjects
Diffraction ,Superconductivity ,Mean square ,Materials science ,Condensed matter physics ,02 engineering and technology ,Soft modes ,021001 nanoscience & nanotechnology ,01 natural sciences ,Instability ,Local structure ,0103 physical sciences ,Hardening (metallurgy) ,Superconducting transition temperature ,010306 general physics ,0210 nano-technology - Abstract
The local structures of 122-type paradium arsenides, namely BaPd2As2 and SrPd2As2, are examined by As K-edge extended x-ray absorption fine structure measurements to find a possible correlation between the variation of their superconducting transition temperature and the local structure. The local atomic distances are found to be consistent with average distances measured by diffraction techniques. The temperature dependence of mean square relative displacements reveal that, while BaPd2As2 is characterized by a local As-Pd soft mode, albeit with larger atomic disorder, SrPd2As2 shows anomalous As-Pd correlations with a kink at similar to 160 K due to hardening by raising temperature. We have discussed implications of these results and possible mechanisms of differing superconducting transition temperature in relation with the structural instability.
- Published
- 2018
44. Determination of the local structure of Sr
- Author
-
Kensei, Terashima, Eugenio, Paris, Eduardo, Salas-Colera, Laura, Simonelli, Boby, Joseph, Takanori, Wakita, Kazumasa, Horigane, Masanori, Fujii, Kaya, Kobayashi, Rie, Horie, Jun, Akimitsu, Yuji, Muraoka, Takayoshi, Yokoya, and Naurang Lal, Saini
- Abstract
The local structure of correlated spin-orbit insulator Sr2-xMxIrO4 (M = K, La) has been investigated by Ir L3-edge extended X-ray absorption fine structure measurements. The measurements were performed as a function of temperature for different dopings induced by substitution of Sr with La or K. It is found that Ir-O bonds have strong covalency and they hardly show any change across the Néel temperature. In the studied doping range, neither Ir-O bonds nor their dynamics, measured by their mean square relative displacements, show any appreciable change upon carrier doping, indicating the possibility of nanoscale phase separation in the doped system. On the other hand, there is a large increase of the static disorder in Ir-Sr correlation, larger for K doping than La doping. Similarities and differences with respect to the local lattice displacements in cuprates are briefly discussed.
- Published
- 2018
45. Fermi level tuning of Ag-doped Bi
- Author
-
Eri, Uesugi, Takaki, Uchiyama, Hidenori, Goto, Hiromi, Ota, Teppei, Ueno, Hirokazu, Fujiwara, Kensei, Terashima, Takayoshi, Yokoya, Fumihiko, Matsui, Jun, Akimitsu, Kaya, Kobayashi, and Yoshihiro, Kubozono
- Subjects
Article - Abstract
The temperature dependence of the resistivity (ρ) of Ag-doped Bi2Se3 (AgxBi2−xSe3) shows insulating behavior above 35 K, but below 35 K, ρ suddenly decreases with decreasing temperature, in contrast to the metallic behavior for non-doped Bi2Se3 at 1.5–300 K. This significant change in transport properties from metallic behavior clearly shows that the Ag doping of Bi2Se3 can effectively tune the Fermi level downward. The Hall effect measurement shows that carrier is still electron in AgxBi2−xSe3 and the electron density changes with temperature to reasonably explain the transport properties. Furthermore, the positive gating of AgxBi2−xSe3 provides metallic behavior that is similar to that of non-doped Bi2Se3, indicating a successful upward tuning of the Fermi level.
- Published
- 2018
46. Determination of the local structure of Sr2-xMxIrO4(M = K, La) as a function of doping and temperature
- Author
-
Eugenio Paris, Kazumasa Horigane, Keisuke Kobayashi, Jun Akimitsu, T. Wakita, Kensei Terashima, Naurang L. Saini, Yuji Muraoka, M. Fujii, R. Horie, Eduardo Salas-Colera, Boby Joseph, Takayoshi Yokoya, and Laura Simonelli
- Subjects
Mean square ,Materials science ,FOS: Physical sciences ,General Physics and Astronomy ,02 engineering and technology ,01 natural sciences ,Static disorder ,Local structure ,Condensed Matter - Strongly Correlated Electrons ,Condensed Matter::Materials Science ,Physics and Astronomy (all) ,Condensed Matter::Superconductivity ,Lattice (order) ,0103 physical sciences ,Cuprate ,Physical and Theoretical Chemistry ,010306 general physics ,Condensed Matter - Materials Science ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed matter physics ,Doping ,Materials Science (cond-mat.mtrl-sci) ,021001 nanoscience & nanotechnology ,Condensed Matter::Strongly Correlated Electrons ,0210 nano-technology ,Néel temperature - Abstract
The local structure of correlated spin-orbit insulator Sr$_{2-x}$M$_x$IrO$_4$ (M = K, La) has been investigated by Ir L$_3$-edge extended x-ray absorption fine structure measurements. The measurements were performed as a function of temperature for different dopings induced by substitution of Sr with La or K. It is found that Ir-O bonds have strong covalency and they hardly show any change across the N\'eel temperature. In the studied doping range, neither Ir-O bonds nor their dynamics, measured by their mean square relative displacements, show any appreciable change upon carrier doping, indicating possibility of a nanoscale phase separation in the doped system. On the other hand, there is a large increase of the static disorder in Ir-Sr correlation, larger for K doping than La doping. Similarities and differences with respect to the local lattice displacements in cuprates are briefly discussed., Comment: Main text: 6 pages, 4 figures, Supplemental information: 2 pages, 2 figures
- Published
- 2018
47. Distinct local structure of superconducting Ca10M4As8(Fe2As2)5(M=Pt,Ir)
- Author
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Naoki Nishimoto, Takanori Wakita, Olivier Proux, Takumi Kimura, Takashi Mizokawa, Kazutaka Kudo, Satoshi Ioka, Daisuke Mitsuoka, Takayoshi Yokoya, Minoru Nohara, Naurang L. Saini, Kazunori Fujimura, and Eugenio Paris
- Subjects
Superconductivity ,Crystallography ,Materials science ,0103 physical sciences ,02 engineering and technology ,021001 nanoscience & nanotechnology ,010306 general physics ,0210 nano-technology ,01 natural sciences ,Local structure - Published
- 2017
48. The electronic structure of Ag
- Author
-
Takanori, Wakita, Eugenio, Paris, Kaya, Kobayashi, Kensei, Terashima, Muammer Yasin, Hacisalihoglu, Teppei, Ueno, Federica, Bondino, Elena, Magnano, Igor, Píš, Luca, Olivi, Jun, Akimitsu, Yuji, Muraoka, Takayoshi, Yokoya, and Naurang L, Saini
- Abstract
We have studied the valence electronic structure of Ag
- Published
- 2017
49. Superconductivity in aromatic hydrocarbons
- Author
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Takayoshi Yokoya, Shino Hamao, Yoshihiro Kubozono, Taihei Jabuchi, Masanari Izumi, Hidenori Goto, Katsuya Shimizu, Lu Zheng, Takashi Kambe, Huyen Nguyen, Tomoko Kagayama, Yusuke Sakai, and Masafumi Sakata
- Subjects
chemistry.chemical_classification ,Superconductivity ,Materials science ,Condensed matter physics ,Transition temperature ,Energy Engineering and Power Technology ,Phenanthrene ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,chemistry.chemical_compound ,Hydrocarbon ,chemistry ,Picene ,Electrical resistivity and conductivity ,Condensed Matter::Superconductivity ,A15 phases ,Physics::Chemical Physics ,Electrical and Electronic Engineering ,Aromatic hydrocarbon - Abstract
‘Aromatic hydrocarbon’ implies an organic molecule that satisfies the (4 n + 2) π-electron rule and consists of benzene rings. Doping solid aromatic hydrocarbons with metals provides the superconductivity. The first discovery of such superconductivity was made for K-doped picene (K x picene, five benzene rings). Its superconducting transition temperatures ( T c ’s) were 7 and 18 K. Recently, we found a new superconducting K x picene phase with a T c as high as 14 K, so we now know that K x picene possesses multiple superconducting phases. Besides K x picene, we discovered new superconductors such as Rb x picene and Ca x picene. A most serious problem is that the shielding fraction is ⩽15% for K x picene and Rb x picene, and it is often ∼1% for other superconductors. Such low shielding fractions have made it difficult to determine the crystal structures of superconducting phases. Nevertheless, many research groups have expended a great deal of effort to make high quality hydrocarbon superconductors in the five years since the discovery of hydrocarbon superconductivity. At the present stage, superconductivity is observed in certain metal-doped aromatic hydrocarbons (picene, phenanthrene and dibenzopentacene), but the shielding fraction remains stubbornly low. The highest priority research area is to prepare aromatic superconductors with a high superconducting volume-fraction. Despite these difficulties, aromatic superconductivity is still a core research target and presents interesting and potentially breakthrough challenges, such as the positive pressure dependence of T c that is clearly observed in some phases of aromatic hydrocarbon superconductors, suggesting behavior not explained by the standard BCS picture of superconductivity. In this article, we describe the present status of this research field, and discuss its future prospects.
- Published
- 2015
50. Control of Fermi Level by Variation of Charge Ordering State in Yb1-xTixFe2O4
- Author
-
Hiroyuki Okazaki, Takanori Wakita, Hiroshi Yamamoto, Takayoshi Yokoya, Tetsushi Fukura, Naoshi Ikeda, Tomoko Nagata, and Nobuyuki Iwata
- Subjects
Materials science ,Condensed matter physics ,Fermi level ,Quantum oscillations ,Fermi energy ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Shubnikov–de Haas effect ,symbols.namesake ,0103 physical sciences ,symbols ,Fermi liquid theory ,010306 general physics ,0210 nano-technology ,Pseudogap ,Fermi gas ,Quasi Fermi level - Published
- 2016
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