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21世紀COEセミナー「Field-induced re-entrant superconductivity in ferromagnetic URhGe」

日時 平成18年(2006年)10月6日(金)16:30〜17:30
場所 理学研究科H棟3階 コミュニケーションスペース
講師 I. Sheikin (Grenoble High Magnetic Field Laboratory, Grenoble, France)
題目 Field-induced re-entrant superconductivity in ferromagnetic URhGe
概要 Recently superconductivity has been observed to appear and co-exist with ferromagnetism in several materials. URhGe is unique amongst them in that bulk superconductivity occurs at zero pressure; superconductivity (Tc = 0.3 K) co-exists with ferromagnetism (TCurie = 9.5 K) at low magnetic field. A spontaneous rotation of the ordered magnetic moment was observed at a magnetic field, HM = 12 Tesla, applied parallel to the b-axis of the orthorhombic crystal structure (perpendicular to the low-field easy-axis direction, the c-axis). Surprisingly, superconductivity re-appears around this spin-rotation transition. When the magnetic field is inclined from b to c-axis, the transition moves to higher fields and becomes second order at a few degrees, thus giving rise to a quantum critical point. However, when the magnetic field is rotated from b to the hard a-axis the transition remains weakly first order and always occurs as far as the field component along the b-axis reaches HM = 12 Tesla. The re-entrant superconductivity closely follows the angular dependence of the spin-rotation transition and was traced up to 28 Tesla. The intrinsic relationship between the two phenomena will be discussed.

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