Superconductivity Induced by Longitudinal Ferromagnetic Fluctuations in UCoGe

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磁石でありながら超伝導にもなる物質の超伝導発現の新しい仕組みを解明－磁石が生み出す超伝導－. 京都大学プレスリリース. 2012-02-07.From detailed angle-resolved NMR and Meissner measurements on a ferromagnetic (FM) superconductor UCoGe (TCurie∼2.5 K and TSC∼0.6 K), we show that superconductivity in UCoGe is tightly coupled with longitudinal FM spin fluctuations along the c axis. We found that magnetic fields along the c axis (H∥c) strongly suppress the FM fluctuations and that the superconductivity is observed in the limited magnetic-field region where the longitudinal FM spin fluctuations are active. These results, combined with model calculations, strongly suggest that the longitudinal FM spin fluctuations tuned by H∥c induce the unique spin-triplet superconductivity in UCoGe. This is the first clear example that FM fluctuations are intimately related with superconductivity.