铁基超导体AFe2-ySe2(A = K,Tl,Cs,Rb)的核磁共振和缪子自旋共振研究

项目名称： 铁基超导体AFe2-ySe2(A = K,Tl,Cs,Rb)的核磁共振和缪子自旋共振研究

项目编号： No.11274268

项目类型： 面上项目

立项/批准年度： 2013

项目学科： 数理科学和化学

项目作者： 宁凡龙

作者单位： 浙江大学

项目金额： 80万元

中文摘要： 铁基高温超导体的一些物理机制还不清楚。在新发现的AFe2-ySe2(A=K, Tl,Cs,Rb)体系中，超导配对对称性问题，反铁磁相和超导相的竞争和共存问题，Fe原子空位和超导的关系等物理问题还存在着争议。我们利用核磁共振(NMR)和缪子自旋共振（MuSR）这两种局域微观测量手段，对AFe2-ySe2体系展开研究。我们通过测量核磁共振谱、奈特位移和自旋-晶格弛豫率，来研究超导态下电子的静态、动态自旋磁化率和轨道磁化率。我们通过缪子自旋共振测量超导体的穿透深度，然后分析比较NMR和muSR数据来研究超导配对对称性。在欠掺杂区域，我们利用核磁共振具有位置选择性的特点以及缪子自旋共振测量有序相体积分数的优势，研究反铁磁相和超导相的共存问题，同时寻找赝能隙和自旋玻璃态存在的实验证据，以及自旋涨落、载流子浓度和铁原子空位之间的依赖关系，及其对超导的贡献。

中文关键词： 铁基超导体；核磁共振；缪子自旋共振；反铁磁涨落；自旋动力学

英文摘要： The physical properties of Fe-based high temperature superconductors have not been fully understood. The superconducting paring symmetry in the newly discovered AFe2-ySe2(A=K,Tl,Cs,Rb) family are still in debate. Meanwhile whether antiferromagnetic phase coexists or competes with superconducting phase are still controversial. We utilize local probes NMR (Nuclear Magnetic Resonance) and MuSR(Muon Spin Rotation/Relaxation/Resonance) to investigate the physical properties of a series of AFe2-ySe2(K,Tl,Cs,Rb) crystals. We deduce the intrinsic static and dynamic spin susceptibility and orbital susceptibility in the superconducting state from the measurement of NMR lineshape, Knight shifts and spin-lattice relaxation rates. In combination with NMR results from the same piece of crystal, we investigate the pairing symmetry through the measurement of penetration depth by muSR. NMR is a site-selective local probe, and muSR has the advantage to determine the volume fraction of ordered phases. We conduct both NMR and muSR measurements in the underdoped region to investigate the coexistence/competition problem between superconducting and antiferromagnetic phases, and searching for the microscopic experimental evidence of pseudogap and spin galss. We investigate the relation between spin fluctuations and carrier concentratio

英文关键词： Fe based superconductors；NMR；muSR；antiferromagnetic spin fluctuations；spin dynamics