Spin fluctuations driving superconductivity in uranium-based ferromagnets; Comparison between URhGe and UCoGe

強磁性超伝導を誘起する磁気揺らぎ; URhGeとUCoGeの比較

徳永 陽  

Tokunaga, Yo

ウランを含む遍歴強磁性超伝導体UGe2, URhGe, UCoGeでは強磁性と超伝導がミクロに共存する。このことは強磁性揺らぎを媒介としたスピン三重項超伝導の存在を直感的に示唆している。ウラン系の遍歴強磁性超伝導は、磁気揺らぎによる超伝導のメカニズムを実験的に検証する格好の舞台を与えており、低エネルギーの磁気揺らぎを高精度で観測できるNMRはその最も有力な測定手法となっている。講演では、URhGe単結晶でのNMRの結果を中心に、URhGeとUCoGeという2つの超伝導体の比較を行い、強磁性揺らぎと超伝導について議論する予定である。

The field-induced reentrant superconductivity in uranium-based ferromagnet URhGe highlights the close interplay between superconductivity (SC) and magnetism in strongly correlated electron systems. Our NMR experiments in URhGe revealed that the inherent FM fluctuations in URhGe at lower fields is robust to the direction of the applied field, although the field-induced fluctuations at higher fields near HR show strong field-angular dependence. This makes a clear contrast with the case of its sister compound UCoGe, where the FM fluctuations show strong field dependence even at lower fields. We can see that the different character of the FM fluctuations is indeed reflected in their phase diagram of the upper critical field Hc2, which is also unconventional and different between the two compounds. This provides further evidence that the SC is mediated by the FM fluctuations in URhGe and UCoGe.