Understanding of Mechanism for Superconductivity on f-electron Superconductors with No Inversion Symmetry by High-pressure NMR

本项目的目的有两个：一是获得CePt3Si反铁磁态超导能隙的电子信息，二是获得高压下铁磁UIR的微观超导特性。首先，通过反复试验，找到了CePt3Si中Ce、Pt和Si的最佳化学计量比。在外场作用下，我们测量了取向样品上Si和Pt的核磁共振谱。所得结果与以前中子衍射法所报道的磁结构不一致。接下来，我们测量了CePt3Si和非磁性LaPt3Si在宽温度范围内的核弛豫速率随温度的变化。奇怪的是，La系的驰豫速率比Ce系的要高。这两个重要的核磁共振结果将被清楚地解释，这些结果将发表在一些期刊上。还测量了通过超导转变温度(T_C)的奈特位移与温度的关系。平行于c轴的奈特位移，即自旋磁化率没有发生任何变化，这导致了CePt3Si中的奇宇称库珀对。太长的相干长度使我们无法找到恰好低于T_c的核弛豫速率的详细行为，即使是用场循环核磁共振进行的。因此，在不久的将来，我们应该尝试重新测量松弛速率，为野外循环测量提供最佳参数。不幸的是，虽然我们已经在其他参考样品中成功地找到了IR信号，但我们在铁磁和顺磁状态的UIR中找不到IR核磁共振信号。无论如何，CePt3Si和UIR的样品对于超导态和正常态的异常行为都是非常重要的，因此我们计划进行核磁共振实验，以暂时找到有趣的结果。(298字)

The purpose of this project is the following two issues : one is to get the electronic information on the superconducting energy gap appearing in the antiferromagnetic state of CePt3Si, the other is to get the microscopic superconducting character of ferromagnetic UIr under high pressure. First of all, we found the best stoichiometry of Ce, Pt and Si in CePt3Si by trial and error. After that we measured the NMR spectra for Si and Pt on the aligned sample under external field. The obtained results were not consistent with the magnetic structure reported previously by the neutron diffraction study. Next, we measured the temperature-dependence of nuclear relaxation rate for the wide temperature range on CePt3Si and non-magnetic LaPt3Si. Strangely enough, the relaxation rate of La system is higher than that of Ce system. Both important NMR results will be clearly explaned, which will be published in some journals. The temperature dependence of Knight shift through the superconducting transition temperature (Tc) was also measured. The Knight shift, namely the spin susceptibility, parallel to the c-axis did not show any change, which leads to the Cooper-pairs of odd parity in CePt3Si. Too long coherence length prevented us from finding the detailed behavior of nuclear relaxation rate just below Tc, even if performed by the field-cycling NMR. So we should try to measure again the relaxation rate with best parameters for the field-cycling measurements in the near future. Unfortunately, we could not find Ir NMR signals in UIr for the ferromagnetic and paramagnetic states, although already succeeded in finding Ir signals in other reference samples. Anyhow, both samples of CePt3Si and UIr are so important for unusual behaviors in the superconducting and normal states that we plan to perform the NMR, experiments to find interesting results for the time being. (298 words)