NMR study of the Peculiar Superconducting Mixed State in the Np Superconductor

在<27><27>0.7 - 11 T的宽外场范围内，测量了重费米子超导体NpPd_5Al_2的核自旋-晶格弛豫速率1/T^^ _1。我们发现1/T^^<27>_1在低于H^~ 3 T的低场s下表现出强烈的场依赖性行为，这归因于N^^ p-A^^ l之间的非类自旋交叉弛豫<237><27>。基于交叉弛豫过程的分析，首次对巡游5 f电子系统中Np核弛豫速率1/^ τ进行了定量估计<237>。估计值1/^<237>τ^~ 6×10^7 s^<-1>，温度变化很小，低于NMR弛豫时间的分辨率，表明直接观察N^^<237>p NMR信号是非常困难的，至少在顺磁状态下是如此。提出了<237>在T^~ 1 K超导态直接观测N^^ p NMR的可能性。

A^^<27> l nuclearspin-lattice relaxation rate 1/T^^<27>_1 has been measured in heavy fermion superconductor NpPd_5Al_2 for a wide range of external fields between 0.7 and 11T. We found that 1/T^^<27>_1 exhibits a strong, fields-dependence behavior at low field s below H^～ 3T, which is attributed to unlike-spin cross relaxation between N^^<237> p-A^^<27> l. An analysis based on the cross relaxation process allows us to make the first quantitative estimation of the Np nuclear relaxation rate 1/^<237>τin an itinerant 5f electron system. The estimated values of 1/^<237>τ^～ 6×10^7 s^<-1>, with a weak temperature variation, are below the resolution of NMR relaxation time, indicating that a direct observation of the N^^<237> p NMR signal would be very difficult, at least in the paramagnetic state. It is proposed that a direct observation of N^^<237> p NMR might be possible in the superconducting state at T^～ 1K.