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

本研究计划利用核磁共振/核磁共振技术，通过杂质和载流子掺杂效应，研究S=1/2自旋梯体系中的量子相干和反常磁性。在有缝隙的自旋1/2海森堡双程梯形化合物SRCu2O3中，阐明了La)诱导的交错极化和反铁磁长程有序。由沿两支的准一维(Q1D)诱导的交错极化得到的关联长度x1^3/a即使在x=0.001和0.005的情况下也比x0/a长得多，T无关的x1^3/a被标度为平均距离D^1；在锌和镍掺杂中，Av&gt；=1/(2x)；在杂质之间的La掺杂中，D^&lt；Av&gt；=1/x，例如，当x=0.001，在锌掺杂中，当D^&lt；Av&gt；=500时，估算出Xi^0/a-50。显著展宽的NQR谱明确地识别了与锌和镍掺杂中的AF-LRO相关的AF矩的出现。在中间的…周围相当均匀的AF时刻在1.4K时，杂质之间有更多的e-Cu位是0.04Mubeta数量级的，其方向是沿a轴的。AF磁矩的空间变化是指数型的，其xx^0/a=8(x=0.01)和4.5(x=0.02)与掺锌时的LISP基本相同。研究发现，一旦杂质破坏了短程共振价键(RVB)态与带隙的量子相干，即使很弱的阶梯间相互作用也能显著地增强Q1D-IISP。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。我们研究了由Cu2O^3梯子和CuO^2链组成的空穴掺杂的两腿梯形化合物Sr^&lt；2.5&gt；Ca^&lt；11.5&gt；Cu^&lt；24&gt；O^&lt；41&gt；在T^M=2.2K以下的三维磁序。我们发现小的磁矩-0.02Mubeta自发地排列在梯子上，而大的磁矩-0.56Mubeta或磁性的Cu位占据了大约四分之一的链。光电导测量结果表明，这种三维磁序是在梯子上形成钉扎类CDW态所驱动的一种协同现象。较少

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