In order to identify the spin contribution to superconducting pairing compatible with the so-called “hidden order”, ${}^{29}\mathrm{Si}$ nuclear magnetic resonance measurements have been performed using a high-quality single crystal of ${\mathrm{URu}}_2{\mathrm{Si}}_2$. A clear reduction of the ${}^{29}\mathrm{Si}$ Knight shift in the superconducting state has been observed under a magnetic field applied along the crystalline $c$ axis, corresponding to the magnetic easy axis. These results provide direct evidence for the formation of spin-singlet Cooper pairs. Consequently, results indicating a very tiny change of the in-plane Knight shift reported previously demonstrate extreme uniaxial anisotropy for the spin susceptibility in the hidden order state.

中文翻译：

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利用核磁共振在URu2Si2中具有强单轴各向异性的自旋单重态配对的证据

为了确定对超导配对的自旋贡献与所谓的“隐藏顺序”兼容， ${}^{29}硅$ 核磁共振测量是使用高质量的单晶硅进行的 ${\mathrm{乌鲁}}_{\mathrm{2个}}{硅}_{\mathrm{2个}}$。明显减少${}^{29}硅$ 在沿晶体施加的磁场下观察到超导态的奈特位移 $C$轴，对应于磁易轴。这些结果为自旋单重库珀对的形成提供了直接的证据。因此，结果表明先前报道的面内奈特位移的微小变化证明了在隐藏有序状态下自旋磁化率具有极大的单轴各向异性。