研究者詳細 - 伊藤　孝寛

論文 - 伊藤　孝寛

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Electronic structure of the surface states of the Zr3SnC2 MAX phase 査読有り国際共著

Takahiro Ito, Thierry Ouisse, Manaya Mita, Kiyohisa Tanaka, Laurent Jouffret, Hanna Pazniak, and Serge Quessada

Physical Review B 108 巻頁： 235145 2023年12月

Electronic structure of Cr2AlC as observed by angle-resolved photoemission spectroscopy

Ito, T; Pinek, D; Fujita, T; Nakatake, M; Ideta, SI; Tanaka, K; Ouisse, T

PHYSICAL REVIEW B 96 巻 ( 19 ) 2017年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Physical Review B

We investigate the electronic band structure and Fermi surfaces (FSs) of Cr2AlC single crystals with angle-resolved photoemission spectroscopy. We evidence hole bands centered around the M points and electron bands centered around the Γ point in reciprocal space. Electron and hole bands exhibit an open, tubular structure along the c axis, confirming the quasi-two-dimensional character of this highly anisotropic, nanolamellar compound. Dependence of the photoionization cross sections on beam light polarization and orientation allows us to assess the orbital character of each observed band locally. Despite some differences, density functional theory calculations show a good agreement with experiment.

DOI： 10.1103/PhysRevB.96.195168

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Electronic structure of V2AlC 査読有り

Pinek, D; Ito, T; Ikemoto, M; Nakatake, M; Ouisse, T

PHYSICAL REVIEW B 98 巻 ( 3 ) 頁： 035120 2018年7月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Physical Review B

We report an experimental and theoretical study of the electronic band structure and Fermi surfaces (FSs) of V2AlC single crystals using angle-resolved photoemission spectroscopy and density functional theory (DFT) calculations. We provide evidence of the existence of equivalent, complex hole FSs with a nearly tubular form along the c axis, and of an intricate electron FS exhibiting tubes parallel to c connected to one another by smaller tubes with axes parallel to the ab plane. The electron FS thus exhibits a small delocalization along the c axis. The local orbital character of each observed band is experimentally and theoretically assessed. DFT calculations show an excellent agreement with experiment. We also report the observation of an unstable surface state.

DOI： 10.1103/PhysRevB.98.035120

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Accelerating X-ray photoemission spectroscopy measurements using Bayesian super-resolution 査読有り

Shunta Harada, Kota Tsujimori, Toyokazu Nomoto, Takahiro Ito

Japanese Journal of Applied Physics 63 巻頁： 048001 2024年4月

Electronic and Thermal Properties of Nb2CCl2 MXenes 査読有り国際共著

H. Pazniak, T. Ouisse, U. Wiedwald, J. Gonzalez-Julian, T. Ito, F. Wilhelm, A. Rogalev, S. Quessada

Open Ceramics 18 巻頁： 100579 2024年3月

Electronic structure of the surface states of the Zr3SnC2 MAX phase

Ito T., Ouisse T., Mita M., Tanaka K., Jouffret L., Pazniak H., Quessada S.

Physical Review B 108 巻 ( 23 ) 2023年12月

出版者・発行元：Physical Review B

We synthesized cm-sized single crystals of the nanolamellar compound Zr3SnC2 and performed angle-resolved photoemission spectroscopy (ARPES). A challenging problem to be solved, when studying electronic structure with ARPES, is to differentiate the surface and bulk electronic bands. We found that just after cleavage, the ARPES signal of Zr3SnC2 is dominated by surface states with well-defined energy dispersions. The (1 × 1) periodicity and the very good match of the electronic structure measured by ARPES with the DFT predictions indicate the absence of surface reconstruction. Mechanical cleavage happens at the Sn-Zr plane boundary, and the ARPES results are consistent with a top surface divided into locally unaltered regions covered with Sn atoms and regions terminated with Zr atoms. We provide a thorough analysis of these surface state bands. Longer-lived surface states are attributed to the Sn-terminated areas. DFT indicates that the surface bands of the Sn-terminated surface do not only involve Sn p orbitals, but also d orbitals of the Zr atoms lying closest to the surface. The orbital nature of the surface bands is further ascertained by ARPES.

DOI： 10.1103/PhysRevB.108.235145

Scopus

グラフェンとHex-Au(001)再構成表面の軌道混成によるバンドギャップの形成

寺澤知潮, 松永和也, 林直輝, 伊藤孝寛, 田中慎一郎, 保田諭, 朝岡秀人

表面と真空 66 巻 ( 9 ) 頁： 525 - 530 2023年9月

Control of rotation angles of multilayer graphene on SiC (0001) by substrate off-direction and angle 査読有り

Ryotaro Sakakibara, Jianfeng Bao, Naoki Hayashi, Takahiro Ito, Hiroki Hibino, Wataru Norimatsu

Journal of Physics: Condensed Matter 35 巻頁： 014002 2023年6月

Magnetic and transport properties of chiral antiferromagnetic Co2-xPdxMo3N thin films( vol 13, 025138, 2023)

Qiang, BW; Fukasawa, T; Hajiri, T; Ito, T; Hihara, T; Asano, H

AIP ADVANCES 13 巻 ( 4 ) 2023年4月

出版者・発行元：AIP Advances

The unit for the left axis in Fig. 2(a) in the original article is not correct.1 This erratum provides the corrected version of Fig. 2(a) with the corrected axis unit. This is a minor correction, and the discussion based on the data presented in Fig. 2(a) is not affected. (Figure Presented). There are some text errors in the original article.1 On page 3, second paragraph, “μΩcm” is corrected as “μΩ cm.” On page 3, third paragraph, “fit for a I–V curve. . .” is corrected as “fit for an I–V curve. . ..” On page 3, first paragraph, “k-space” is corrected as “k-space.” In Fig. 2 caption, “MS” is corrected as “MS.” In Fig. 3 caption, “ϕ = 0.63 eV” is corrected as “ϕ = 0.63 eV.” These text errors do not affect the validity of the results of the original article.

DOI： 10.1063/5.0152258

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Magnetic and transport properties of chiral antiferromagnetic Co2-xPdxMo3N thin films

Qiang, BW; Fukasawa, T; Hajiri, T; Ito, T; Hihara, T; Asano, H

AIP ADVANCES 13 巻 ( 2 ) 2023年2月

出版者・発行元：AIP Advances

Hall transport and non-collinear magnetoresistance (NCMR) are studied for a chiral antiferromagnet (AFM) with the filled β-Mn-type structure. Magnetic and transport properties of epitaxial thin films of Co2-xPdxMo3N revealed that, in addition to a canted antiferromagnetic behavior above room temperature, thin films with x = 1.01∼1.38 exhibited a transition to a spin spiral state with a higher magnetic moment below TSR of around 50 K, which was assigned to a spin reorientation transition. The low-temperature phase shows both large anomalous Hall effect (AHE) and topological Hall effect (THE). Upon the transition to the canted AFM phase existing up to room temperature, the large AHE still persists with vanishing THE. The behavior of the Hall transport properties coupled with NCMR signals in the current-perpendicular-to-the plane configuration shows the formation of topological spin textures with locally antiferromagnetic order. The present results open the way for the study of topological antiferromagnetic spin textures, manipulation of their properties, and for future spintronic applications.

DOI： 10.1063/9.0000454

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Band gap opening in graphene by hybridization with Au (001) reconstructed surfaces

Terasawa, T; Matsunaga, K; Hayashi, N; Ito, T; Tanaka, SI; Yasuda, S; Asaoka, H

PHYSICAL REVIEW MATERIALS 7 巻 ( 1 ) 2023年1月

出版者・発行元：Physical Review Materials

Au(001) surfaces exhibit a complex reconstructed structure [Hex-Au(001)] comprising a hexagonal surface and square bulk lattices, yielding a quasi-one-dimensional corrugated surface. When graphene was grown on this surface, the periodicity of the corrugated surface was predicted to change the electronic structure of graphene, forming bandgaps and new Dirac points. Furthermore, the graphene-Au interface is promising for bandgap generation and spin injection due to band hybridization. Here, we report the angle-resolved photoemission spectroscopy and density functional calculation of graphene on a Hex-Au(001) surface. The crossing point of the original and replica graphene πbands showed no bandgap, suggesting that the one-dimensional potential was too small to modify the electronic structure. A bandgap of 0.2 eV was observed at the crossing point of the graphene πand Au 6sp bands, indicating that the bandgap is generated using hybridization of the graphene πand Au 6sp bands. We discussed the hybridization mechanism and concluded that the R30 configuration between graphene and Au and an isolated electronic structure of Au are essential for effective hybridization between graphene and Au. We anticipate that hybridization between graphene πand Au 6sp would result in spin injection into graphene.

DOI： 10.1103/PhysRevMaterials.7.014002

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Magnetic phase diagram and vanishing topological Hall effect in the chiral antiferromagnet Co2-x Pdx Mo3N

Qiang, BW; Fukasawa, T; Hajiri, T; Ito, T; Hihara, T; Asano, H

JAPANESE JOURNAL OF APPLIED PHYSICS 61 巻 ( 12 ) 2022年12月

出版者・発行元：Japanese Journal of Applied Physics

The magnetic phase diagram and topological Hall effect (THE) are studied by magnetization and transport measurements for chiral antiferromagnet (AFM) Co2-x Pdx Mo3N ( x = 0-1.61) thin films with the filled β-Mn-type chiral structure, which reveals the rich phase diagram in the temperature versus Pd content x plane, where a collinear AFM, a canted AFM, and a low-temperature phase below 50 K are found to exist. For thin films with x = 1.01-1.61, the low-temperature phase shows prominent THE. The formation of the canted AFM phase with the Néel temperature up to 325 K is observed with vanishing THE. These findings establish the chiral antiferromagnetic molybdenum nitrides as a fertile playground for exploring the interplay between chiral antiferromagnetism, topological spin textures, and novel magnetotransport phenomena.

DOI： 10.35848/1347-4065/ac9a92

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Observation of Thickness-Dependent Exchange Interaction in EuO Ultrathin Films

Miyazaki, H; Hajiri, T; Matsunami, M; Inukai, M; Ito, T; Kimura, SI

FRONTIERS IN NANOTECHNOLOGY 4 巻 2022年6月

出版者・発行元：Frontiers in Nanotechnology

The electronic structure of single-crystalline EuO (100) ultrathin films, together with their exchange splitting energy (ΔEEX) and ferromagnetic phase transition temperature (TC), was investigated by temperature- and thickness-dependent angle-resolved photoemission spectroscopy. Both ΔEEX and TC decreased monotonically with decreasing film thickness. The band shift showed an opposite thickness dependence at the Γ and X points, reflecting the balance of the hybridization between the Eu 4f and O 2p states (super-exchange interaction) and between the Eu 4f, O 2p, and Eu 5d states (indirect-exchange interaction). The observed transition from an indirect energy gap in the bulk to a direct gap in the ultrathin films of the ferromagnetic semiconductor EuO could be potential in future spintronic devices.

DOI： 10.3389/fnano.2022.872717

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Observation of a flat band and bandgap in millimeter-scale twisted bilayer graphene 査読有り国際共著

Sato, K; Hayashi, N; Ito, T; Masago, N; Takamura, M; Morimoto, M; Maekawa, T; Lee, D; Qiao, K; Kim, J; Nakagahara, K; Wakabayashi, K; Hibino, H; Norimatsu, W

COMMUNICATIONS MATERIALS 2 巻 ( 1 ) 2021年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Communications Materials

Magic-angle twisted bilayer graphene, consisting of two graphene layers stacked at a special angle, exhibits superconductivity due to the maximized density of states at the energy of the flat band. Generally, experiments on twisted bilayer graphene have been performed using micrometer-scale samples. Here we report the fabrication of twisted bilayer graphene with an area exceeding 3 × 5 mm2 by transferring epitaxial graphene onto another epitaxial graphene, and observation of a flat band and large bandgap using angle-resolved photoemission spectroscopy. Our results suggest that the substrate potential induces both the asymmetrical doping in large angle twisted bilayer graphene and the electron doped nature of the flat band in magic-angle twisted bilayer graphene.

DOI： 10.1038/s43246-021-00221-3

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Fermi surface and band structure of Ti2SnC as observed by angle-resolved photoemission spectroscopy 査読有り国際共著

Pinek, D; Ito, T; Furuta, K; van Bunningen, AJ; Le Fèvre, P; Bertran, F; Ouisse, T

PHYSICAL REVIEW B 104 巻 ( 19 ) 頁： 195118-1 - 195118-9 2021年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Physical Review B

We present an experimental study of the electronic states of the nanolamellar compound Ti2SnC by means of angle-resolved photoemission spectroscopy (ARPES). Experiments were performed on macroscopic single crystals, and the observed Fermi surface and band structure were systematically compared with the output of density functional theory calculations. The fine details of the Fermi surface predicted by theory are duly evidenced by the ARPES measurements. The multiply connected Fermi surface (FS) is formed by a combination of quasi-two-dimensional corrugated tubes and quasi-one-dimensional thin plates, centered on high-symmetry axes and points, respectively. The quasi-one-dimensional FS region displays a clear Dirac-like dispersion. An evanescent surface state is observed in addition to the bulk bands.

DOI： 10.1103/PhysRevB.104.195118

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Angle-resolved Photoemission Study of Solid Electrolytes LixLa(1-x)/3NbO3 Bulk Single Crystal 国際共著

T. Ito, R. Yamamoto, M. Nakatake, S. Ideta, K. Tanaka, Y. Fujiwara and Y. Iriyama

UVSOR Activity Report 2020 48 巻頁： 77 2021年8月

Angle-resolved Photoemission Study of i-MAX Phase Compound (Mo2/3Ho1/3)2AlC2 国際共著

T. Ito, K. Furuta, D. Pinek, M. Nakatake, S. Ideta, K. Tanaka and T. Ouisse

UVSOR Activity Report 2020 48 巻頁： 77 2021年8月

Mo4Ce4Al7C3 : A nanolamellar ferromagnetic Kondo lattice 査読有り

Barbier, M; Wilhelm, F; Pinek, D; Furuta, K; Ito, T; Kim, Y; Magnier, M; Braithwaite, D; Valiska, M; Opagiste, C; Barsoum, MW; Ohresser, P; Otero, E; Le Fèvre, P; Bertran, F; Garbarino, G; Rogalev, A; Ouisse, T

PHYSICAL REVIEW B 102 巻 ( 15 ) 2020年10月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Physical Review B

Herein we show that Mo4Ce4Al7C3, a recently discovered nanolamellar compound displaying mixed valence, combines Kondo lattice behavior with ferromagnetism. A sizeable magnetization is carried by 3p states of Al as evidenced by a strong x-ray magnetic circular dichroism signal at the K edge of aluminum, whereas no detectable signal was observed at the K edge of carbon and L2,3 edges of molybdenum. These results point out that the ferromagnetic behavior originates in the Ce atoms with 4f1 electronic configuration lying within the Al planes. The evolution with pressure of the mixed valence of Ce atoms in the Mo-C planes determined via Ce L3 x-ray-absorption spectra along with the magnetoresistance measurements across the ferromagnetic transition unambiguously reveal a Kondo behavior. Angle-resolved photoemission spectroscopy and density functional theory confirm a certain degree of Ce 4f electron delocalization. More generally, conduction electrons are not restricted to lie in the MoC planes but are also delocalized in the Al planes.

DOI： 10.1103/PhysRevB.102.155121

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Near Fermi level electronic structure of Ti3SiC2 revealed by angle-resolved photoemission spectroscopy 査読有り

Pinek, D; Ito, T; Furuta, K; Kim, Y; Ikemoto, M; Ideta, SI; Tanaka, K; Nakatake, M; Le Fèvre, P; Bertran, F; Ouisse, T

PHYSICAL REVIEW B 102 巻 ( 7 ) 2020年8月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Physical Review B

An in-depth study of the Fermi surface and electronic structure of the ternary nanolamellar carbide Ti3SiC2 is reported. The outputs of angle-resolved photoemission spectroscopy (ARPES) measured on single crystals and density functional theory calculations are systematically compared. The band structure is found to be dominated by Ti d orbitals near the Fermi level. Band inversions near K points are responsible for the intricate shape of the Ti3SiC2 pockets. Previous theory found that those pockets were giving opposite contributions leading to zero thermoelectric power in polycrystalline samples. Here we directly visualize them by ARPES, describe their precise shape, and examine the way they should behave regarding thermoelectric power. The presence of linear band crossings and the effect of spin-orbit coupling on the near Fermi level electronic structure are discussed, as well as potential consequences for magnetotransport and spin Hall effect.

DOI： 10.1103/PhysRevB.102.075111

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Controlled growth of boron-doped epitaxial graphene by thermal decomposition of a B4C thin film

Norimatsu, W; Matsuda, K; Terasawa, TO; Takata, N; Masumori, A; Ito, K; Oda, K; Ito, T; Endo, A; Funahashi, R; Kusunoki, M

NANOTECHNOLOGY 31 巻 ( 14 ) 頁： 145711 2020年4月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Nanotechnology

We show that boron-doped epitaxial graphene can be successfully grown by thermal decomposition of a boron carbide thin film, which can also be epitaxially grown on a silicon carbide substrate. The interfaces of B4C on SiC and graphene on B4C had a fixed orientation relation, having a local stable structure with no dangling bonds. The first carbon layer on B4C acts as a buffer layer, and the overlaying carbon layers are graphene. Graphene on B4C was highly boron doped, and the hole concentration could be controlled over a wide range of 2 1013 to 2 1015 cm-2. Highly boron-doped graphene exhibited a spin-glass behavior, which suggests the presence of local antiferromagnetic ordering in the spin-frustration system. Thermal decomposition of carbides holds the promise of being a technique to obtain a new class of wafer-scale functional epitaxial graphene for various applications.

DOI： 10.1088/1361-6528/ab62cf

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