NMR Studies of S=1/2 Quantum Spin Systems with either Ladder or Triangular Lattice

具有阶梯或三角形晶格的 S=1/2 量子自旋系统的核磁共振研究

基本信息

批准号：
07454081
负责人：
KITAOKA Yoshio
金额：
$ 1.28万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-07454081/
关键词：
Triangular Lattice Spin Ladder Quantum Spin System Spin Liquid Spin Gap Quantum Criticality NMR Unconventional Superconductivity はしご格子量子スピン NMR

项目摘要

This research project planed to investigate the relationship between the quantum spin fluctuations and anomalous magnetism in S=1/2 quantum spin systems containing either the ladder or triangular lattice. Furthermore, we addressed the impurity and carrier doping effects into two-leg spin ladder systems.We listed the following results.1.Sr_2Cu_3O_5 exhibits the long-range magnetic order below -60 K and is characterized by quantum spin fluctuations above 200 K inherent to three-leg ladder.2.Two-leg ladder compound LaCuO_<2.5> was suggested from the susceptibility measurement to have seemingly a spin gap as in SrCu_2O_3. From the Cu-NMR study, we, however, found that this compound was magnetically ordered below-120 K.A possible competition takes place between the spin liquid state with a spin gap and the magnetic ordered states.3.S=1/2 triangular lattice LiNiO_2 exhibis no long-range order at low-T,although the ferromagnetic exchange interaction is expected among Ni spins from the susceptibility measurement, meaing no frustration. We proposed that the triangular lattice structure make two degenerated orbital states frustrated, leading to some orbital liquid ground states, which prevents the logn-range spin ordering.4.In hole-doped two-leg spin ladder systems, Sr_<14-x>Ca_xCu_<24>O_<41>, magnitude of the spin gap, DELTA=510 K for Ca-undoped one decreases to 270 K for the Ca11.5.5.The spin gap stays constant in going from the Ca9 to the Ca11.5.6.In DELTA <= T,spin dynamics are well characterized by the one-dimensional quantum critical spin fluctuations, despite two chains are exchange-coupled to one another and holes are doped.7.hole carrieres are localized at low T associated with quasi one-dimensional conducting channel in the ladder plane.We have thus clarified novel characteristics of quantum spin fluctuations and anomalous magentism inherent to S=1/2 low-dimesional quantum spin systems. The present reaserch project enabled us to open new frontiers in the field.

该研究项目计划研究包含阶梯晶格或三角晶格的S=1/2量子自旋系统中量子自旋涨落与反常磁性之间的关系。此外，我们还解决了两腿自旋梯系统中的杂质和载流子掺杂效应。我们列出了以下结果：1.Sr_2Cu_3O_5在-60 K以下表现出长程磁序，并以200 K以上固有的量子自旋涨落为特征。三足梯。2.两足梯化合物LaCuO_<2.5>从磁化率测量中可以看出，它看起来像SrCu_2O_3一样具有自旋间隙。然而，从 Cu-NMR 研究中，我们发现该化合物的磁有序度低于-120 K。具有自旋间隙的自旋液态与磁有序态之间可能发生竞争。3.S=1/2 三角晶格LiNiO_2 在低 T 下不表现出长程有序，尽管从磁化率测量中预计 Ni 自旋之间会发生铁磁交换相互作用，这意味着不会受挫。我们提出，三角晶格结构使两个简并轨道态受挫，导致一些轨道液态基态，从而阻碍了logn范围的自旋有序化。4.在空穴掺杂的双腿自旋梯系统中，Sr_<14-x> Ca_xCu_<24>O_<41>，自旋间隙的大小，对于 Ca 未掺杂的，DELTA=510 K 对于 Ca11.5.5 降低到 270 K。自旋间隙保持不变从Ca9到Ca11.5.6的常数。在DELTA <= T中，尽管两条链彼此交换耦合且空穴掺杂，但自旋动力学很好地通过一维量子临界自旋涨落来表征。7．空穴载流子局域于与梯形平面中的准一维导电通道相关的低 T 处。因此，我们阐明了量子自旋涨落和 S=1/2 低维固有的反常磁力的新特征量子自旋系统。目前的研究项目使我们能够在该领域开辟新的前沿。