强磁场下非常规超导体的核磁共振研究

In superconductor research, high-magnetic field is one kind of method to modulate superconducting state. It could be used to unfold the normal state or competing state which is hidden by superconducting state and is one of important methods to study the mechanism of superconductivity. Unconventional superconductor is a new kind of superconducting materials. Compared with conventional superconductor, it has a lot of anomal physical properties and its superconducting mechanism is not completely clear up to now which is still an open question in this field. This project relys on Hefei high magnetic field lab and we plan to build up a low-temperature probe which is suitable for research on condensed matter physics，especially for strongly correlated electonic materials. Based on this, we will conduct nuclear magnetic resonance study on unconventional superconductor under high magnetic field. This project will be concentrated on NMR study of the magnetic-field induced normal state and competing order in both high-Tc cuprates and pnictides. Through measuring the field dependence of NMR spectrum, knight shift and spin-lattice relaxation, we could systematically characterize the magnetic field induced normal state and competing order. Finally, we will try to understand the mechanism of normal state and the correlation between competing order and superconductivity.

在超导体研究中，强磁场是一种调控超导态的有效手段，可以揭示隐藏在超导态之下的“正常态”或“竞争态”等相关物理特性，是进行超导机理研究的重要手段之一。非常规超导体是一类新型的超导材料，它与传统超导材料相比具有许多反常的物理特性，其超导机理到目前仍然没有完全认识清楚，是该领域公认的难点问题。该申请项目将依托于中科院强磁场科学中心实验平台，拟建立一套在强磁场下适用于凝聚态物理研究（特别是关联电子材料）的低温核磁共振探头，并在此基础上开展强磁场下非常规超导体的核磁共振研究。本项目将针对铜氧化合物高温超导体和铁基高温超导体中磁场诱导的低温“正常态”和竞争相进行核磁共振研究，试图通过测量核磁共振波谱、奈特位移和自旋-晶格弛豫率等物理量对磁场的依赖关系，对磁场诱导的“正常态”和竞争相进行系统表征。通过本项目，我们将理解“正常态”的形成机制和竞争相与超导的关系。

本项目的研究目标是围绕非常规超导体以及相关的关联电子体系开展在强磁场下的核磁共振研究，并依托合肥强磁场科学中心进一步完善国内高场核磁共振实验的基础研究平台，推动国内强磁场下的凝聚态核磁共振研究，培养一批具有强磁场下的核磁共振研究经验的尖端科研人员。结合实际的样品生长以及测量平台的条件，我们在项目执行期间针对铁基超导体CsFe2As2、近藤绝缘体SmB6、Ti基超导母体材料BaTi2As2O以及铜砷基新材料YCuAs2开展了系列高场核磁共振研究，最高核磁实验磁场达到25 Tesla（该部分实验在合肥强磁场科学中心完成，是目前国内磁场强度最高的核磁共振实验），并取得了重要的实验进展。另外，我们还依托合肥强磁场科学中心，围绕中心的核磁共振级磁体开展了系列的核磁测量平台建设，并在核磁共振实验相关器件方面也取得了进展。总体来说，项目达到了预期计划的效果并在平台建设以及科学研究两方面都取得了一定的成绩。