铁磁超导体UGe2的磁相变研究

Heavy-fermion superconductivity has been discovered in nearly forty systems in which cerium or uranium manifests an important composite element. The strong Coulomb repulsion in the 4f/5f shells and the strong hybridization with the conduction electrons give rise to the formation of heavy quasi-particles, and the complex interactions can lead to a variety of different ground states like magnetically ordered or superconductive states. Heavy-fermion superconductors deserve detailed studies due to the similarity to cuprates and iron pnictides, with the focus on the mechanisms behind. The coexistence of ferromagnetism and superconductivity was recently first discovered in UGe2, which is in strong contrast to the old opinion that ferromagnetism was thought to be completely antagonistic to superconductivity. Thus, efforts in this work should be made in the synthesis of UGe2 compound as well as the research of low-temperature magnetic transitions . Comprehensive studies in these properties will certainly intensify our understanding of actinide heavy-fermion systems, making contributions for further investigations in modern theory and experimental technology of condesed matter.

稀土元素铈和锕系元素铀是已发现的近四十种重费米子超导体中最常见的组成元素。它们4f/5f电子壳层中的强库伦排斥及其与传导电子的杂化导致了重的准粒子的形成，并由于复杂的电子相互作用而呈现出不同的基态，如磁有序态和超导态。作为典型的非常规超导体，重费米子超导体背后蕴含着与铜氧化物高温超导体、铁基超导体等相似的作用机理，非常值得我们去研究。特别是近年来铁磁超导体UGe2的发现，使人们对非常规超导现象以及铁磁和超导相互作用的认识面临前所未有的挑战，铁磁和超导是可以共存的。因此，本项目拟开展铁磁超导体UGe2的合成及低温磁相变研究，对锕系重费米子体系研究的深入开展、现今凝聚态理论和实验技术的发展均具有非常重要的科学意义。

稀土元素铈和锕系元素铀是已发现的近四十种重费米子超导体中最常见的组成元素。它们4f/5f电子壳层中的强库伦排斥及其与传导电子的杂化导致了重的准粒子的形成，并由于复杂的电子相互作用而呈现出不同的基态，如磁有序态和超导态。作为典型的非常规超导体，重费米子超导体背后蕴含着与铜氧化物高温超导体、铁基超导体等相似的作用机理，非常值得我们去研究。特别是近年来铁磁超导体UGe2的发现，使人们对非常规超导现象以及铁磁和超导相互作用的认识面临前所未有的挑战，铁磁和超导是可以共存的。本项目开展铁磁超导体UGe2的制备合成及低温磁相变研究。利用高质量单晶样品的基础物性（电阻率、磁化率、比热等）研究数据，课题组基于二流体模型和5f电子的局域/巡游双重特性，针对UGe2磁相变相图提出了一个与传统观点存在显著差异的新论断，不仅给出了巡游准粒子与局域5f磁矩共存的直接的实验证据，还对准粒子行为进行了精准的描述，为超导出现的物理机制、介于局域-巡游边界的奇异量子态和量子相变研究开启了新的篇章。