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Unconventional supercondnuctivity in the itinerant ferromagnet UGe$$_2$$; $$^{73}$$Ge-NQR study under pressure

強磁性物質UGe$$_2$$における新奇な超伝導状態について; 高圧下$$^{73}$$Ge-NQRによる研究

原田 敦之*; 川崎 慎二*; 椋田 秀和*; 北岡 良雄*; 芳賀 芳範; 山本 悦嗣; 大貫 惇睦; 伊藤 公平*; Haller, E. E.*; 播磨 尚朝*

Harada, Atsushi*; kawasaki, Shinji*; Mukuda, Hidekazu*; Kitaoka, Yoshio*; Haga, Yoshinori; Yamamoto, Etsuji; Onuki, Yoshichika; Ito, Kohei*; Haller, E. E.*; Harima, Hisatomo*

遍歴強磁性超伝導物質UGe$$_2$$$$^{73}$$Ge-NQRによる研究結果を報告する。低温・低圧相であるFM1と高温・高圧相FM2の臨界圧力$$P_x$$近辺で測定を行った。核緩和時間$$T_1$$は低温で温度に対して線型に振る舞い、コヒーレンスピークはない。実験結果は、スピン三重項の超伝導がアップスピンバンドで実現しており、ダウンスピンバンドでは超伝導ギャップが開いていないと考えると統一的に理解できる。

The superconducting characteristics on the itinerant ferromagnetic superconductor UGe$$_2$$ have been investigated via the $$^{73}$$Ge-NQR measurements under pressure ($$P$$) near the critical pressure $$P_x$$ where the first-order transition takes place from the low-temperature ($$T$$) and low-$$P$$ ferromagnetic phase (FM2) to high-$$T$$ and high-$$P$$ one (FM1). The measurements of nuclear spin-lattice relaxation rate $$T_1$$ have revealed a power-law like behavior as $$T^n$$ without the coherence peak, whereas at low temperatures, it deviates from the $$T^n$$ dependence to a $$T$$-linear like behavior. These results that depend on the pressure are well understood in terms of non-unitary spin-triplet pairing state where the ferromagnetic up-spin band is gapped, but the down-spin band remains gapless at the Fermi level. We will argue an intimate relationship of the onset of SC with FM1 and FM2.

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パーセンタイル:91.96

分野:Physics, Condensed Matter

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