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70. Electronic properties across metal-insulator transition in ��-pyrochlore-type CsW2O6 epitaxial films

Author

Soma, Takuto, Yoshimatsu, Kohei, Horiba, Koji, Kumigashira, Hiroshi, and Ohtomo, Akira

Subjects
Strongly Correlated Electrons (cond-mat.str-el), FOS: Physical sciences
Abstract

In CsW2O6, which undergoes a metal-insulator transition (MIT) at 213 K, the emergence of exotic properties associated with rattling motion of Cs is expected owing to its characteristic ��-pyrochlore-type structure. However, a hurdle for crystal growth hampers elucidation of detailed properties and mechanisms of the MIT. Here we report on the epitaxial growth of ��-pyrochlore-type CsW2O6 films and their electronic properties across the MIT. Using pulsed-laser deposi-tion technique, we grew single-crystalline CsW2O6 films exhibiting remarkably lower resistivity compared with a poly-crystalline bulk and sharp MIT around 200 K. Negative magnetoresistance and positive Hall coefficient were found, which became pronounced below 200 K. The valence-band and core-levels photoemission spectra indicated the drastic changes across the MIT. In the valence band photoemission spectrum, the finite density of states was observed at the Fermi level in the metallic phase. In contrast, an energy gap appeared in the insulating phase. The split of W 4f core-level spectrum suggested the charge disproportionation of W5+ and W6+ in the insulating phase. The change of spectral shape in the Cs 4d core levels reflected the rattling motion of Cs+ cations. These results strongly suggest that CsW2O6 is a novel material, in which MIT is driven by the charge disproportionation associated with the rattling motion., 8 pages, 6 figures

Published
2018
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72. Direct Synthesis of Metastable λ-Phase Ti3O5Films on LaAlO3(110) Substrates at High Temperatures

Author

Yoshimatsu, Kohei and Kumigashira, Hiroshi

Abstract

High-quality metastable λ-phase trititanium pentoxide (λ-Ti3O5) films were grown via pulsed-laser deposition at a very high growth temperature. The λ-Ti3O5was directly formed on the substrate surface without any detectable transient layers. The obtained monoclinic λ-Ti3O5films contained almost single domains, in which the relative fraction of 180° rotational domains was below 1% on pseudocubic LaAlO3substrates. The successful synthesis of metastable λ-Ti3O5epitaxial films enables the utilization of their rich functionalities.

Published
2022
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87. Anisotropic Charge Distribution Induced by Spin Polarization in La0.6Sr0.4MnO3 Thin Films Studied by X-ray Magnetic Linear Dichroism

Author

Shibata, Goro, primary, Yoshimatsu, Kohei, additional, Ishigami, Keisuke, additional, Harano, Takayuki, additional, Takahashi, Yukio, additional, Sakamoto, Shoya, additional, Nonaka, Yosuke, additional, Kadono, Toshiharu, additional, Furuse, Mitsuho, additional, Fuchino, Schuichiro, additional, Okano, Makoto, additional, Fujihira, Jun-ichi, additional, Uchida, Akira, additional, Watanabe, Kazunori, additional, Fujihira, Hideyuki, additional, Fujihira, Seiichi, additional, Tanaka, Arata, additional, Kumigashira, Hiroshi, additional, Koide, Tsuneharu, additional, and Fujimori, Atsushi, additional

Published
2018
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89. Anisotropic spin-density distribution and magnetic anisotropy of strained La1−xSr x MnO3 thin films: angle-dependent x-ray magnetic circular dichroism

Author

Shibata, Goro, primary, Kitamura, Miho, additional, Minohara, Makoto, additional, Yoshimatsu, Kohei, additional, Kadono, Toshiharu, additional, Ishigami, Keisuke, additional, Harano, Takayuki, additional, Takahashi, Yukio, additional, Sakamoto, Shoya, additional, Nonaka, Yosuke, additional, Ikeda, Keisuke, additional, Chi, Zhendong, additional, Furuse, Mitsuho, additional, Fuchino, Shuichiro, additional, Okano, Makoto, additional, Fujihira, Jun-ichi, additional, Uchida, Akira, additional, Watanabe, Kazunori, additional, Fujihira, Hideyuki, additional, Fujihira, Seiichi, additional, Tanaka, Arata, additional, Kumigashira, Hiroshi, additional, Koide, Tsuneharu, additional, and Fujimori, Atsushi, additional

Published
2018
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90. Epitaxial Stabilization of Complete Solid-solution β-(AlxGa1–x)2O3(100) Films by Pulsed-laser Deposition

Author

Wakabayashi, Ryo, Yoshimatsu, Kohei, Hattori, Mai, Lee, Jung-Soo, Sakata, Osami, and Ohtomo, Akira

Abstract

We report on the lattice and band structures of complete solid-solution β-(AlxGa1–x)2O3(x= 0–1) films that were epitaxially grown on β-Ga2O3(100) substrates by using oxygen-radical-assisted pulsed-laser deposition. We found that oxygen-plasma treatment of the substrate surface was the key to achieving a two-dimensional growth mode of not only β-Ga2O3but also θ-Al2O3with the β-gallia structure. The band gap of β-(AlxGa1–x)2O3increased from 4.51 ± 0.02 eV (x= 0) to 6.91 ± 0.02 eV (x= 1). The x-dependence of the (100) spacing and band gap showed the anomalous bowing behavior, as the curvatures changed around x∼ 0.5. This tendency was ascribed to the different arrangements of the Al and Ga cations along their tetrahedral and octahedral site preference in the β-gallia structure. We also fabricated a short-period superlattice composed of θ-Al2O3and β-Ga2O3layers to verify the sharp interface from the X-ray diffraction profile.

Published
2021
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91. β-Ga2O3用ITOオーミック電極

Author

OSHIMA, Takayoshi, Wakabayashi, Ryo, Hattori, Mai, Hashiguchi, Akihiro, Kawano, Naoto, Sasaki, Kohei, Masui, Takekazu, Kuramata, Akito, Yamakoshi, Shigenobu, Yoshimatsu, Kohei, and Ohtomo, Akira

Published
2016

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