The putative spin-triplet superconductor UTe₂ has an Ising-like magnetic anisotropy, indicating the Cooper pair spins parallel to the easy-axis. However, the upper critical field for the hard-axis direction is much larger than that for the easy-axis, implying the strong suppression of the Pauli depairing effect even for the hard-axis direction. This observation is consistent with the recent NMR measurements which show the tiny decrease of the Knight shift below the transition temperature T_c for hard-axis magnetic fields. We clarify that these behaviors are naturally understood as a result of multi-orbital f-electron bands with total angular momentum j = 5/2. Taking into account spin–orbit couplings for an orthorhombic structure, we demonstrate that for hard-axis magnetic fields, the decrease of the spin susceptibility below T_c and the Pauli depairing effect are strongly suppressed.

中文翻译：

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j电子超导的顺磁效应及其在UTe2中的应用

假定的自旋三重态超导体UTe ₂具有类似Ising的磁各向异性，表明Cooper对平行于易轴自旋。但是，硬轴方向的上临界场比易轴方向的上临界场大得多，这意味着即使在硬轴方向上，泡利去对效应的抑制也很强。该观察结果与最近的NMR测量结果一致，后者显示对于硬轴磁场，奈特位移在转变温度T _c以下略有下降。我们澄清，由于总角动量为j的多轨道f电子能带，这些行为自然被理解= 5/2。考虑到正交结构的自旋-轨道耦合，我们证明了对于硬轴磁场，在T _c以下的自旋磁化率下降和Pauli配对效应被强烈抑制。