Browsing by Author "Hirata, Y"

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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.
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    Structural, electrical, magnetic, and optical properties of iron-based ladder compounds BaFe2(S1−xSex)3
    (American Physical Society, 2020-07-01) Imaizumi, S; Aoyama, T; Kimura, R; Sasaki, K; Nambu, Y; Avdeev, M; Hirata, Y; Ikemoto, Y; Moriwaki, T; Imai, Y; Ohgushi, K
    We performed a comprehensive study on structural, electrical, magnetic, and optical properties for iron-based ladder materials BaFe2(S1−xSex)3(0≤x≤1), which shows pressure-induced superconductivity in the vicinity of the Mott transition at x=0 and 1. We obtain a complete electronic phase diagram in a temperature-composition plane, which reveals that the magnetic ground state switches from the stripe-type to the block-type phase without any intermediate phase at x=0.23 with increasing x. This behavior is in sharp contrast to the filling controlled system Ba1−xCsxFe2Se3, in which a paramagnetic state down to the lowest temperature is realized between two magnetic ordered states. The structural transition, which is considered to be relevant to the orbital order, occurs far above the magnetic transition temperature. The magnetic and structural transition temperatures exhibit a similar composition dependence, indicating a close relationship between magnetic and orbital degrees of freedom. In addition, we found that charge dynamics are considerably influenced not only by the magnetic order but also by the structural change (orbital order) from the detailed measurements of electrical resistivity and optical conductivity spectra. We discuss the magnetism and orbital order by comparing the experimental results with the proposed theory based on the multiorbital Hubbard model. The relationship between the charge dynamics and the magnetic/orbital order is also discussed. ©2020 American Physical Society
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    Temperature and composition phase diagram in the iron-based ladder compounds Ba1−xCsxFe2Se3
    (American Physical Society, 2015-05-28) Hawai, T; Nambu, Y; Ohgushi, K; Du, F; Hirata, Y; Avdeev, M; Uwatoko, Y; Sekine, Y; Fukazawa, H; Ma, J; Chi, S; Ueda, Y; Yoshizawa, H; Sato, TJ
    We investigated the iron-based ladder compounds (Ba,Cs)Fe2Se3. Their parent compounds BaFe2Se3 and CsFe2Se3 have different space groups, formal valences of Fe, and magnetic structures. Electrical resistivity, specific heat, magnetic susceptibility, x-ray diffraction, and powder neutron diffraction measurements were conducted to obtain a temperature and composition phase diagram of this system. Block magnetism observed in BaFe2Se3 is drastically suppressed with Cs doping. In contrast, stripe magnetism observed in CsFe2Se3 is not so fragile against Ba doping. A new type of magnetic structure appears in intermediate compositions, which is similar to stripe magnetism of CsFe2Se3, but interladder spin configuration is different. Intermediate compounds show insulating behavior, nevertheless a finite T-linear contribution in specific heat was obtained at low temperatures. ©2015 American Physical Society