NMR on Spin Dynamics in Spin Ladder & High-T Superconductor

在这个项目中，通过NMR/NQR测量以及磁化率和热容测量，研究了梯状化合物和过渡金属氧化物等强相关体系的异常电子性质。这些研究是在爱荷华州立大学、库尔恰托夫研究所和苏黎世大学的合作下完成的。用Cu-NMR和NQR研究了Sr_<14-x>A_1Cu_<24>O_<41> （A=Ca和La）单晶中空穴掺杂对链和阶梯位自旋间隙的影响。我们确定了Sr_<14-x>La_xCu_<24>O_<41>的3*x*6链的Cu矩的长程反铁磁序。实验结果表明，铜自旋在链内的磁序为铁磁性，而在链间的磁序为反铁磁性。场诱导的交错矩远高于T_N。感应场的温度依赖性服从类居里-魏斯特性。这些结果表明，交错场与有序铜链矩无关，而归因于阶梯铜自旋的磁性。讨论了阶梯Cu位点场致交错矩的可能来源。此外，我们还详细研究了Sr_<2.5>Ca_<11.5>Cu_<24>O_<41>高空穴掺杂化合物的磁序性质。我们还研究了一些过渡金属氧化物中金属-绝缘体（MI）的转变。金属-绝缘体跃迁附近的磁态和局部电子态已经在原始论文中进行了讨论和介绍。我们还在法国强相关电子系统国际会议、法国电子导体核磁共振研讨会和高t核磁共振研讨会上发表了结果。瑞士超导体。

In this project, unusual electronic properties of the strongly correlated systems such as ladder compounds and transition metal oxides have been investigated by NMR/NQR measurements aa well as magnetic susceptibility and heat capacity measurement. These researches were done under the collaboration of Iowa State University, Kurchatov Institute and Zurich University.Hole-doping effects on the spin gaps for both the chain and the ladder site are investigated by Cu-NMR and NQR for single crystals of Sr_<14-x>A_1Cu_<24>O_<41> (A=Ca and La). We have confirmed longrange antiferromagnetic order of Cu moments of the chain for 3*x*6 of Sr_<14-x>La_xCu_<24>O_<41>. The experimental results indicate that the magnetic order of Cu spins in the chain is ferromagnetic within the chain, and is antiferromagnetic for the inter-chains. The field-induced staggered moments appears far above T_N. The temperature dependence of the induced field obeys the Curie-Weiss like behavior. These results suggest that the staggered field is not related to the ordered Cu chain moments but is attributed to the magnetic nature of the ladder Cu spins. Possible origins of the field-induced staggered moments at the ladder Cu site are discussed. In addition, we have investigated detail nature of the magnetic order which is observed for a highly hole-doped compound of Sr_<2.5>Ca_<11.5>Cu_<24>O_<41>.We have also studied metal-insulator (MI) transition in some transition metal oxides. Magnetic and local electronic states near the Metal-Insulator transition have been discussed and presented in original papers We have also presented the results at the lnternational Conference on Strongly Correlated Electron Systems in France, Workshop on NMR in Elecronic Conductors, France, and Colloquium on Magnetic Resonance in High-T.Superconductors, Switzerland.