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

在0.7~11T的外场范围内，测量了重费米子超导体NPPd_5Al_2中的核自旋-晶格驰豫速率1/T^&lt；27&gt；1。我们发现，在H^~3T以下的低场S下，1/T^&lt；27&gt；_1表现出强烈的场依赖型行为，这归因于N^&lt；237&gt；p-A^&lt；27&gt；L之间的不同自旋交叉驰豫。基于交叉驰豫过程的分析使我们首次定量地估计了巡游5f电子系统的NP核弛豫速率1/^&lt；237&gt；τ。1/^&lt；237&gt；τ^~6×10^7 S^&lt；-1&gt；的估计值低于核磁共振弛豫时间的分辨率，这表明直接观测N^&lt；237&gt；p核磁共振信号将是非常困难的，至少在顺磁状态下是这样。提出了在T^~1K超导状态下直接观测N^^&lt；237&gt；p核磁共振的可能性。

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.