Browsing by Author "Kasahara, S."

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    Charge-neutral fermions and magnetic field-driven instability in insulating YbIr3Si7
    (Springer Nature, 2022) Sato, Y.; Suetsugu, S.; Tominaga, T.; Kasahara, Y.; Kasahara, S.; Kobayashi, T.; Kitagawa, S.; Ishida, K.; Peters, R.; Shibauchi, T.; Nevidomskyy, A. H.; Qian, L.; Morosan, E.; Matsuda, Y.
    Kondo lattice materials, where localized magnetic moments couple to itinerant electrons, provide a very rich backdrop for strong electron correlations. They are known to realize many exotic phenomena, with a dramatic example being recent observations of quantum oscillations and metallic thermal conduction in insulators, implying the emergence of enigmatic charge-neutral fermions. Here, we show that thermal conductivity and specific heat measurements in insulating YbIr3Si7 reveal emergent neutral excitations, whose properties are sensitively changed by a field-driven transition between two antiferromagnetic phases. In the low-field phase, a significant violation of the Wiedemann-Franz law demonstrates that YbIr3Si7 is a charge insulator but a thermal metal. In the high-field phase, thermal conductivity exhibits a sharp drop below 300 mK, indicating a transition from a thermal metal into an insulator/semimetal driven by the magnetic transition. These results suggest that spin degrees of freedom directly couple to the neutral fermions, whose emergent Fermi surface undergoes a field-driven instability at low temperatures.
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    In-plane electronic anisotropy resulted from ordered magnetic moment in iron-based superconductors
    (American Physical Society, 2020) Wu, S.-F.; Zhang, W.-L.; Thorsmølle, V.K.; Chen, G.F.; Tan, G.T.; Dai, P.C.; Shi, Y.G.; Jin, C.Q.; Shibauchi, T.; Kasahara, S.; Matsuda, Y.; Sefat, A.S.; Ding, H.; Richard, P.; Blumberg, G.
    We study the in-plane electronic anisotropy in the parent compounds of several families of Fe-based superconductors (BaFe2As2, EuFe2As2, NaFeAs, LiFeAs, FeSe, and LaFeAsO) by polarization-resolved Raman scattering. We measure intensity of the fully symmetric c-axis vibration of As atom mode in the XY scattering geometry and notice that the mode's intensity is significantly enhanced below the magnetostructural transition only for compounds showing magnetic ordering. In particular, we find that the intensity ratio of this As phonon in the XY vs. XX scattering geometries is proportional to the square of the ordered magnetic moment. We relate this As phonon intensity enhancement below the Néel temperature in iron pnictides to in-plane electronic anisotropy induced by the collinear spin-density wave order.