【摘要】 强关联物理一直是高温超导体研究的前沿领域,被认为是与高温超导电性的微观机理密切相关.2008年铁基超导体的发现给高温超导体研究带来了一个全新的材料体系,其中,中国科学技术大学高温超导研究团队对铁基超导体的发现做出了重大的贡献.随着对铁基超导体研究的深入,人们发现铁基超导体不同于以往发现的铜基高温超导体,其电子关联效应表现出较弱的特征,强关联物理与高温超导电性之间的必然性受到了极大挑战.在理论上,人们认为铁基超导体依然具有强关联物理的特征,只是其表现形式由于多轨道以及洪特耦合的原因而呈现出轨道选择的特点.探索铁基超导体中的强关联物理成为了当前高温超导体研究的一个前沿问题.本文综述了我们对重空穴掺杂的铁基超导体AFe₂As₂（A=K, Rb, Cs）系列材料的核磁共振（NMR）研究。相关研究结果表明电子的关联性在重空穴掺杂区间表现得尤为突出,诸多特征与理论所描述的轨道选择的莫特物理相吻合:首先,电子的局域性与巡游性可以共存,并在低温下形成类似于重费米子体系的电子相干态;其次,基于位置选择的NMR探测,我们实现了轨道选择的局域磁化率测量,进一步证实了铁基超导体中轨道选择的电子关联效应;最后,我们还首次在重空穴掺杂的CsFe₂As₂体系中观测到一个全新的电子向列相.以上这些现象揭示了铁基超导体与铜基超导体以及重费米子超导体类似的强关联特征,将有助于建立统一的高温超导机理.更多还原

【Abstract】 Strong correlated physics has been a frontier field in the research of high-temperature superconductors and is considered to be closely related to the microscopic mechanism of high-temperature superconductivity. The discovery of iron-based superconductors in 2008 brought a brand new material platform to the research of high-temperature superconductors. And the research team from the University of Science and Technology of China has made significant contributions to the discovery of iron-based superconductors. With further in-depth study of iron-based superconductors, it has been found that iron-based superconductors are different from copper-based high-temperature superconductors with weaker electronic correlation effects. The picture based on strongly correlated physics for high-temperature superconductivity is greatly challenged. Theoretically, iron-based superconductors are still considered to have the features of the strong correlated physics, but their manifestations are featured by orbital selectivity due to multiple orbitals and the Hund’s coupling. The exploration of strong correlated physics in iron-based superconductors has become a frontier issue in current research of high-temperature superconductors. In this paper, our nuclear magnetic resonance（NMR） studies on the heavily hole-doped iron-based superconductors AFe₂As₂（A=K, Rb, Cs） were reviewed. Our results indicate that the electronic correlation effect is very strong in the heavily hole-doped region and many features are consistent with the orbital selective Mott physics. First, the localization and itinerancy of electrons can coexist, and an electronic coherent state similar to the heavy fermion system emerges at the low temperature; secondly, based on site-selective NMR detection, orbital-selective local spin susceptibility measurements were achieved, further confirming the orbital-selective electron correlation effects in iron-based superconductors; finally, for the first time, a new electronic nematic state was observed in heavily hole-doped CsFe₂As₂ systems. These findings reveal similar strong correlation features between iron-based superconductors and copper-based superconductors and heavy fermion superconductors, which will help to establish a unified high-temperature superconducting mechanism.更多还原