Akimasa Ohnishi
Yamagata University
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Featured researches published by Akimasa Ohnishi.
Applied Physics Express | 2016
Mamoru Kitaura; Kei Kamada; Shunsuke Kurosawa; Junpei Azuma; Akimasa Ohnishi; Akihiro Yamaji; Kazuhiko Hara
From measuring absorption spectra of cerium-doped Gd3Al2Ga3O12 (Ce:GAGG) and undoped GAGG crystals at low temperatures under UV-light irradiation, we find that they exhibit a broad band at around 12000 cm−1. This band is enhanced by high-temperature annealing under a hydrogen atmosphere. On the basis of present experimental results, the UV-induced band is assigned to shallow electron traps of defect complexes associated with oxygen vacancies. The UV-induced band completely disappears with Mg2+ codoping. We conclude that the Mg2+ codoping has the effect of inhibiting the formation of shallow electron traps, which realizes a faster scintillation response of Ce:GAGG.
Physical Review Letters | 2013
Heon-Jung Kim; Ki-Seok Kim; Junfeng Wang; V.A. Kulbachinskii; Koji Ogawa; Minoru Sasaki; Akimasa Ohnishi; Mamoru Kitaura; Y. Y. Wu; Liang Li; I. Yamamoto; Junpei Azuma; Masao Kamada; V. Dobrosavljevic
We propose a phase diagram for Fe(x)Bi2Te3 (0≤x≤0.1) single crystals, which belong to a class of magnetically bulk-doped topological insulators. The evolution of magnetic correlations from ferromagnetic to antiferromagnetic gives rise to topological phase transitions, where the paramagnetic topological insulator of Bi2Te3 turns into a band insulator with ferromagnetic-cluster glassy behavior around x∼0.025, and it further evolves to a topological insulator with valence-bond glassy behavior, which spans over the region from x∼0.03 up to x∼0.1. This phase diagram is verified by measuring magnetization, magnetotransport, and angle-resolved photoemission spectra with theoretical discussions.
Japanese Journal of Applied Physics | 2007
Kunihiko Matsumura; Akimasa Ohnishi; Minoru Sasaki; Takayoshi Kakuta; Masato Kurihara; Masatomi Sakamoto
Zn1-xMgxO fine bulk crystals with Mg contents of x = 0–0.15 are fabricated by a complex decomposition method, in which starting complexes of Zn1-xMgx(C2O4)2H2O hetero metal coordination polymers, synthesized with [Zn(C2O4)2(H2O)2]2- dioxalato complex ions, are decomposed at a relatively low temperature in air. Their structural and optical characterizations are carried out by X-ray powder diffraction and diffuse reflection measurements, respectively. Zn1-xMgxO nanocrystals with x = 0–0.10 are also fabricated by the thermal decomposition of Zn1-xMgx(C2O4)2H2O coordination-polymer nanocrystals synthesized with dioxalato complex ions inside reverse micelles. Samples are characterized by optical absorption measurements.
Physical Review B | 2011
Heon-Jung Kim; Ki-Seok Kim; Mun Dae Kim; Su-Hyung Lee; Jae-Ho Han; Akimasa Ohnishi; Mamoru Kitaura; M. Sasaki; Akihiro Kondo; Koichi Kindo
Topological states of matter challenge the paradigm of symmetry breaking, characterized by gapless boundary modes and protected by the topological property of the ground state. Recently, angle-resolved photoemission spectroscopy (ARPES) has revealed that semiconductors of Bi
Japanese Journal of Applied Physics | 1999
Akimasa Ohnishi; Nobufumi Mori; Ken-ichi Kan'no
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Journal of the Physical Society of Japan | 1994
Akimasa Ohnishi; Mamoru Kitaura; Hideyuki Nakagawa
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Japanese Journal of Applied Physics | 2014
Azusa Satoh; Mamoru Kitaura; Kei Kamada; Akimasa Ohnishi; Minoru Sasaki; Kazuhiko Hara
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Applied Physics Letters | 2017
Mamoru Kitaura; Junpei Azuma; Manabu Ishizaki; Kei Kamada; Shunsuke Kurosawa; Shinta Watanabe; Akimasa Ohnishi; Kazuhiko Hara
and Bi
Journal of the Physical Society of Japan | 2012
Akimasa Ohnishi; Mamoru Kitaura; Minoru Itoh; Minoru Sasaki
_{2}
Applied Physics Letters | 2011
Koji Ogawa; Minoru Sasaki; Akimasa Ohnishi; Mamoru Kitaura; Hitoshi Fujimoto; Junpei Azuma; Kazutoshi Takahashi; Masao Kamada
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