NMR study of heavy fermion superconductor at low temperatur

在重费米子超导体中，超导性与磁性的相互作用是一个令人感兴趣的课题。特别地，铁磁（F）或反铁磁（AF）自旋涨落的存在导致了在这些系统中实现具有非S波对称性的非常规库珀对态的预测。超导电性的非S特性导致低温下各种物理性质的幂律温度（T）依赖性。我们对URu_2Si_2和UPd_2Al_3进行了NMR/NQR研究，并测量了超导态下^ Ru，^ Si，^ Pd和^ Al的核自旋晶格弛豫时间（T_1）<101><29><105><27>。观察到的1/T_1的T依赖性与T^3成正比，这表明在超导能隙中存在线节点。在UPd_2Al_3中，<27>观察到^ Al的Knight位移减小，表明超导体具有偶宇称d波对称性。相反，在URu_2Si_2中没有观察到Knight位移的降低。因此，在URu_2Si_2中仍然存在p波或f波超导的可能性.单晶URu_2Si_2的精确测量仍在继续，以确定其对称性。

The interplay between superconductivity and magnetism in the heavy fermion (HF) superconductors is a fascinating subject. In particular, the presence of ferromagnetic (F) or antiferromagnetic (AF) spin fluctuations has led to the prediction that an unconventional Cooper pair state with non S-wave symmetry is realized in these systems. The non S-character of the superconductivity induces the power-law temperature (T) dependence of the various physical properties at low temperatures. We have performed NMR/NQR studies in URu_2Si_2 and UPd_2Al_3, and measured the nuclear spin lattice relaxation time (T_l) of ^<101>Ru, ^<29>Si, ^<105>Pd and ^<27>Al in the superconducting state. The observed T-dependence of 1/T_1's (of all nucli) is proportional to T^3, which indicated the existence of line nodes in the superconducting energy gap. In UPd_2Al_3, the decrease of ^<27>Al Knight shift was observed, which shows the superconductivity has the even parity d-wave symmetry. On the contrary, any decrease of Knight shift was not observed in URu_2Si_2. Hence the possibility of p- or f- wave superconductivity in URu_2Si_2 still remains. The accurate measurements of the single crystal URu_2Si_2 is still continuing to determine the symmetry.