Browsing by Author "Kawakami, T"

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    Magnetic and transport properties of AFe_2Se_3 (A= Ba and Cs)
    (The Physical Society of Japan, 2012-03-05) Du, F; Ohgushi, K; Sasaki, R; Matsubayashi, K; Uwatoko, Y; Kawakami, T; Nambu, Y; Avdeev, M; Sato, TJ; Ueda, Y
    The orthorhombic AFe2Se3 (A=Ba and Cs) have attracted much attention due to the possibility of superconducivity AFe2Se3 The crystal structure of 14Fe2Se3 can be described as double chains of [Fe2Se3】formed by the edge sharing FeSe4 tetrahedra. We synthesize AFezSe3 single crystalline samples by the self flux method firstly, then studies the magnetic and transport properties under ambient and high pressure. BaFe2Se3 shows a semiconducting behavior. With increasing pressure 8 GPa, the charge gap of BaFe2Se3 gradually decreases; however, the ground state is still insulating at 8 GPa. Interestingly, CBFe2Se3 also shows a Semiconducting behavior although the formally mixed valence state of Fe ions. Mossbauer spectra of CsFe2Se3 indicate that electronic state of Fe ions is unique, ruling out the possibility of charge ordering. In addition, a magnetic transition at 170K is suggested from the hyperfine filed splitting in the Mossbauer spectra and neutron diffraction analysis．
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    Pressure-induced superconductivity in the iron-based ladder material BaFe2S3
    (Springer Nature, 2015-07-20) Takahashi, H; Sugimoto, A; Nambu, Y; Yamauchi, T; Hirata, Y; Kawakami, T; Avdeev, M; Matsubayashi, K; Du, F; Kawashima, C; Soeda, H; Nakano, S; Uwatoko, Y; Ueda, Y; Sato, TJ; Ohgushi, K
    All the iron-based superconductors identified so far share a square lattice composed of Fe atoms as a common feature, despite having different crystal structures. In copper-based materials, the superconducting phase emerges not only in square-lattice structures but also in ladder structures. Yet iron-based superconductors without a square-lattice motif have not been found, despite being actively sought out. Here, we report the discovery of pressure-induced superconductivity in the iron-based spin-ladder material BaFe2S3, a Mott insulator with striped-type magnetic ordering below ∼120 K. On the application of pressure this compound exhibits a metal–insulator transition at about 11 GPa, followed by the appearance of superconductivity below Tc = 14 K, right after the onset of the metallic phase. Our findings indicate that iron-based ladder compounds represent promising material platforms, in particular for studying the fundamentals of iron-based superconductivity. © 2015, Nature Publishing Group
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    Stripelike magnetism in a mixed-valence insulating state of the Fe-based ladder compound CsFe2Se3
    (American Physical Society, 2012-06-28) Du, F; Ohgushi, K; Nambu, Y; Kawakami, T; Avdeev, M; Hirata, Y; Watanabe, Y; Sato, TJ; Ueda, Y
    Structural and electronic properties of the Fe-based spin-ladder compound CsFe2Se3 was investigated by means of resistivity, susceptibility, specific heat, Mossbauer, and neutron diffraction measurements. Despite the single-site nature in a mixed-valence state, the ground state is a magnetic insulator characterized by a charge gap similar to 0.34 eV and an antiferromagnetic transition temperature 175 K. The magnetic structure was stripelike, with magnetic moments of 1.77(6)mu(B) coupled ferromagnetically (antiferromagnetically) along the rung (leg) direction. Both the insulating behavior and stripelike ordering can be understood by assuming extra carriers delocalized on the rung. Our findings reveal that CsFe2Se3 is an appealing compound with the stripelike magnetic structure in an insulating state among Fe-based compounds, and provide significant supplemental insight into the magnetism of Fe-based superconductors. © 2012, American Physical Society.