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

在本项目中，我们通过NMR/NQR测量以及磁化率和热容测量研究了梯形化合物和过渡金属氧化物等强关联体系的异常电子性质。本研究是在爱荷华州州立大学、库尔恰托夫研究所和苏黎世大学的合作下进行的，利用Cu-NMR和NQR研究了空穴掺杂对Sr_<14-x>A_1Cu_<24>O_<41>（A=Ca和La）单晶链和梯位自旋能隙的影响。我们确定了Sr_ La_xCu_ O_（3 × 6）链中Cu磁矩的长程反铁磁序<14-x><24><41>。实验结果表明，链中Cu自旋的磁序在链内是铁磁的，链间是反铁磁的。在T_N以上的位置出现了场致交错矩。感生场的温度依赖性服从Curie-Weiss类行为。这些结果表明，交错场是不相关的有序铜链的时刻，但归因于梯形铜自旋的磁性性质。场诱导的交错时刻在梯形铜网站的可能来源进行了讨论。此外，我们还研究了高空穴掺杂的Sr_ Ca_ Cu_ O_3化合物的磁有序的详细性质<2.5><11.5><24><41>，并研究了一些过渡金属氧化物的金属-绝缘体（MI）转变。本文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瑞士高温超导磁共振学术讨论会上，介绍了有关结果。

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.