NMR Studies on Ferromagnetic Superconductor UCoGe

Orateur : Prof. K. ISHIDA (Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502 Japan)

In the seminar, I will present our 59Co nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) studies on the single crystalline ferromagnetic (FM) superconductor UCoGe, which exhibits FM ordering at TCurie =2.5 K and superconductivity below TSuper = 0.57 K [1]. We studied the coexistence state from the microscopic point of view, and showed that superconductivity occurs in the FM region and the both phenomena originate from U 5f electrons [2]. We also studied the spin-dynamic properties from the measurements of 1/T1 and Knight shift, and found that both static and dynamic susceptibilities are ferromagnetic with strong Ising anisotropy along the c axis [3]. In addition, from the angle-resolved NMR measurements, we found that the magnetic field along the c axis (H//c) strongly suppresses both the FM Ising-type fluctuations and superconductivity in the same manner [4]. These results strongly suggest that the characteristic FM fluctuations tuned by H//c induce the unique spin-triplet superconductivity in UCoGe, which is also supported by the recent Knight-shift results [5]. These studies have been performed in the collaboration with T. Hattori,1 Y. Ihara (Hokkaido Univ.),1 Y. Nakai (Tokyo Metropolitan Univ.),1 Y. Tada (ISSP, Univ. of Tokyo),1 S. Fujimoto,1 N. Kawakami,1 E. Ozaki,2 K. Deguchi,2 N. K. Sato,2 and T. Yamamura3. 2Department of Physics, Graduate School of Science, Nagoya University, Nagoya 464-8602 Japan 3Institute of Materials Research, Tohoku University, Sendai, 980-8577, Japan References [1] N. T. Huy et al., Phys. Rev. Lett. 99, 067006 (2007). [2] T. Ohta et al., J. Phys. Soc .Jpn. 79, 023707 (2010). [3] Y. Ihara et al., Phys. Rev. Lett. 105, 206403 (2010). [4] T. Hattori et al. Phys. Rev. Lett. 108, 066403 (2012). [5] T. Hattori et al. Phys. Rev. B 88, 085127 (2013).

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