Study of long-range order of charges and/or spins in low-dimensional cuprates

本文研究了高温超导铜氧化物及相关铜氧化物中的电荷序和自旋序，以获得高温超导机制的一些信息。研究结果如下：1.在部分掺Zn的Bi-2212铜氧化物和La-214铜氧化物中发现了所谓的1/8反常，即空穴浓度p=1/8/Cu时超导性的反常抑制。从μ子自旋弛豫测量中我们还发现，Zn掺杂的Bi-2212和Y-123铜氧化物在p=1/8的低温下自旋关联增强。因此，1/8异常是高T_c铜氧化合物的普遍现象.我们发现La_ Sr_xCu_ Zn_yO_4在x=0.21处的超导电性受到反常的抑制，自旋关联增强<2-x><1-y>。从x=0.21和y=0.01的单晶的中子散射实验中，我们观察到在（π，π）附近的无公度磁峰，这与在p=1/8处观察到的磁峰相似。因此，很可能自旋和空穴的动态条纹顺序被Zn钉扎，导致静态条纹顺序和在x=0.21以及p=1/8.3处的超导性抑制。从以上结果可以看出，在很宽的空穴浓度范围内，自旋和空穴的条纹关联都是存在的，它们可能在高温超导的出现中起着重要的作用.我们从输运测量的角度研究了自旋梯型铜氧化物Sr_<14>Cu_<24>O_3<41>，发现空穴在低温下是成对的，而不是形成电荷密度波。我们还发现，在这个系统中，由于自旋的热导率是非常大的。

We have studied charge and/or spin order in the high-T_c cuprates and related cuprates, in order to obtain some informations on the mechanism of high-T_c superconductivity. The results obtained are as follows.1. We have discovered the so-called 1/8 anomaly, namely, the anomalous suppression of superconductivity at the hole concentration p=1/8 per Cu in the partially Zn-doped Bi-2212 cuprates as well as in the La-214 cuprates. We have also found from the muon-spin-relaxation measurements that the spin correlation is enhanced at low temperatures at p=1/8 in the Zn-doped Bi-2212 and Y-123 cuprates. Accordingly, it is concluded that the 1/8 anomaly is common to the high-T_c cuprates.2. We have discovered anomalous suppression of superconductivity and enhancement of the spin correlation at x=0.21 in La_<2-x>Sr_xCu_<1-y>Zn_yO_4. From the neutron scattering experiment of the single crystal with x=0.21 and y=0.01, we have observed incommensurate magnetic peaks around (π, π), which is similar to those observed at p=1/8. Accordingly, it is very likely that the dynamical stripe order of spins and holes is pinned by Zn, leading to the static stripe order and the suppression of superconductivity at x=0.21 as well as at p=1/8.3. From the above results, it is concluded that the stripe correlations of spins and holes exist in a wide range of hole concentration and that there is a possibility that they play an important role in the appearance of high-T_c superconductivity.4. We have studied the spin ladder cuprate Sr_<14>Cu_<24>O_<41> from the transport measurements, and concluded that holes are paired at low temperatures rather than form charge density wave. We have also found that the thermal conductivity due to spins is anomalously large in this system.