Study on correlation between magnetism and superconductivity in f-electron systems

我们研究了几种典型的重费米子化合物，包括基于ce和u的磁性超导体和基于sm的价态波动材料，在热力学，磁性和输运测量方面以及中子散射技术。我们得到了以下结果。我们揭示了UPd_2Al_3和UNi_2Al_3的自旋动力学，并成功探测到它们的de Haas-van Alphen效应信号。得到了隐藏有序态和超导态共存的URu_2Si_2的压力-温度相图，并发现了一条将隐藏有序态和反铁磁有序态分开的一阶相线（称为佐藤线）。我们还指出，在压力下出现的反铁磁性破坏了超导态。我们观察到UGe_2在压力下的超导转变温度呈双峰结构。在两个临界温度附近的双峰结构是否意味着存在两个不同的超导区，这仍然是一个悬而未决的问题。我们发现，即使在环境压力下，CeRhIn_5也具有超导性。从超导转变温度和尼尔温度的压力依赖性出发，借助于理论模型，我们提出了超导性和反铁磁性在费米表面的一个态上竞争共存。我们构造了典型的混价化合物SmS的压力-温度相图，揭示了所谓的金相中存在赝隙。这清楚地解决了长期以来关于黄金SmS是金属还是半导体的分歧。我们制作了一个加压膨胀和直流磁化实验装置。我们还开发了一种使用木炭泵的3he冰箱。因此，我们揭示了重费米子材料的某些方面，并解决了重费米子物理领域的一些基本问题，尽管潜在的物理问题仍有待解决。少

We have studied several typical heavy fermion compounds, including Ce-and U-based magnetic superconductors and a Sm-based valence fluctuating material, in terms of thermodynamic, magnetic, and transport measurements together with the neutron scattering technique. We obtained the following results.1. We revealed the spin dynamics of UPd_2Al_3 and UNi_2Al_3, and succeeded in detecting de Haas-van Alphen effect signals for them.2. We obtained a pressure-temperature phase diagram of URu_2Si_2 that exhibits the coexistence of hidden order and superconductivity, and revealed a first order phase line (called Sato line) that separates the hidden and antiferromagnetic ordered states. We also indicated that the superconducting state is destroyed by the antiferromagnetism emerging under pressure.3. We observed that the superconducting transition temperature of UGe_2 exhibits a twin peak structure under pressure. It remains an open question whether the twin peak structure at around two critical pr … More essures implies the existence of two different superconducting regions.4. We found that the superconductivity appears even at ambient pressure for CeRhIn_5. From the pressure dependence of the superconducting transition temperature and Neel temperature, with the help of a theoretical model, we suggested that the superconductivity and antiferromagnetism competitively coexists for a state on the Fermi surface.5. We constructed a pressure-temperature phase diagram of the typical mixed valence compound SmS, and revealed the existence of a pseudogap in the so-called golden phase. This clearly resolves the long-standing discrepancy whether golden SmS is a metal or a semiconductor.We constructed an apparatus for dilatation and dc magnetization experiments under pressure. We also developed a _3He refrigerator using a charcoal pump.As a result, we revealed some aspects of the heavy fermion materials and solved some of fundamental problems in the field of the heavy fermion physics, although the underlying physics remains to be resolved. Less