NMR Studies of Quantum Choherence and Magnetism in Spin-Ladder Systems

自旋梯系统中量子相干性和磁性的核磁共振研究

基本信息

批准号：
09440138
负责人：
KITAOKA Yoshio
金额：
$ 8.58万
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：
1997
资助国家：
日本
起止时间：
1997 至 1998
项目状态：
已结题

项目摘要

This research project was planed to investigate by means of NMR/NQR the quantum coherence and anoma-lous magnetism in S=1/2 spin-ladder systems through the impurity and carrier doping effects.Characteristics of impurity (Zn, Ni, and La)-induced staggered polarization (IISP) and antiferromagnetic long-range order (AF-LRO) were clarified in gapped spin-1/2 Heisenberg two-leg ladder compound SrCu^2O^3. A correlation length xi^3/a estimated from a quasi-one-dimensional (Q1D) IISP along the two-leg was found to be much longer even in x=0.001 and 0.005 than xi^0/a. The T-independent xi^3/a is scaled to an average distance D^<AV> = 1/(2x) in the Zn and Ni doping and D^<AV> = 1/x in the La doping between the impurities, for example, xi^0/a -50 is estimated in the Zn doping when D^<AV> = 500 for x=0.001. The significantly broadened NQR spectrum has unambiguously identified the appearance of AF moments associated with the AF-LRO in the Zn and Ni doping. Rather uniform AF moments around the middl … More e Cu sites between the impurities are estimated to be in an order of 0.04 mubeta at 1.4 K with their direction along the a axis. The spatial variation of AF moments is shown to be of exponential type with almost the same xi^0/a = 8 (x=0.01) and 4.5 (x=0.02) as in the LISP for the Zn doping. The Q1D-IISP was found to be dramatically enhanced by an interladder interaction even though so weak, once the impurity breaks up the quantum coherence in the short-range resonating valence bond (RVB) state with the gap. On the other hand, we propose that T^N is determined by a strength of the interladder interaction and a size of S^o. We showed that hole-doped two-leg ladder compound Sr^<2.5>Ca^<11.5>Cu^<24>O^<41> comprising Cu^2O^3 ladders and CuO^2 chains reveals three dimensional (3D) magnetic order below T^M=2.2 K.We found that small moments - 0.02 mubeta are spontaneously ordered on the ladders, whereas large moments - 0.56mubeta or the magnetic Cu sites occupying about one-fourth of the chains. It is suggested that this 3D magnetic order is a cooperative phenomenon driven by the formation of pinned CDW-like state on the ladders which the optical conductivity measurement has clarified. Less

本研究项目计划通过NMR/NQR通过杂质和载流子掺杂效应研究S=1/2自旋梯系统中的量子相干性和反常磁性。杂质（Zn、Ni和La）的特性-在带隙自旋1/2海森堡双腿梯化合物中阐明了诱导交错极化（IISP）和反铁磁长程有序（AF-LRO）即使在 x=0.001 和 0.005 的情况下，从准一维 (Q1D) IISP 估计的 SrCu^2O^3 也比 xi^0/a 长得多。与 T 无关的 xi^3/a 在 Zn 和 Ni 掺杂中缩放为平均距离 D^<AV> = 1/(2x)，并且 D^<AV> = 。 1/x 在 La 掺杂中，例如，当 D^<AV> = 500（对于 x=0.001）时，在 Zn 掺杂中估计 xi^0/a -50 显着展宽的 NQR 光谱已明确识别了外观。与 Zn 和 Ni 掺杂中的 AF-LRO 相关的 AF 矩估计在杂质之间的 middl … More e Cu 位点周围相当均匀。 1.4 K 处的 0.04 mubeta 的方向沿 a 轴，AF 矩的空间变化呈指数型，几乎相同 xi^0/a = 8 (x=0.01) 和 4.5 (x=0.02)。正如在 Zn 掺杂的 LISP 中一样，一旦杂质破坏了量子，Q1D-IISP 就会通过梯间相互作用显着增强。另一方面，我们提出 T^N 是由阶梯间相互作用的强度和 S^o 的大小决定的。包含Cu^2O^3梯子和CuO^2链的掺杂两腿梯子化合物Sr^<2.5>Ca^<11.5>Cu^<24>O^<41>揭示了三维（3D）磁序低于 T^M=2.2 K。我们发现小矩 - 0.02 mubeta 在梯子上自发排序，而大矩 - 0.56mubeta 或占据约四分之一链的磁性 Cu 位点表明这种 3D 磁性。有序是由阶梯上形成类似 CDW 的状态驱动的协同现象，光学电导率测量已经阐明了这一点。