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

我们研究了高t_c铜酸盐和相关铜酸盐中的电荷和/或自旋顺序，以期获得一些关于高t_c超导机理的信息。得到的结果如下：1。我们发现了所谓的1/8异常，即在部分掺锌的Bi-2212铜酸盐和La-214铜酸盐中，在空穴浓度p=1/8 / Cu时超导性的异常抑制。我们还从介子自旋弛豫测量中发现，在p=1/8的低温下，掺锌的Bi-2212和Y-123铜酸盐的自旋相关得到增强。因此，1/8异常是高t_c铜的共同特征。我们发现了La_<2-x>Sr_xCu_<1-y>Zn_yO_4在x=0.21处超导性的异常抑制和自旋相关的增强。从x=0.21, y=0.01的单晶中子散射实验中，我们在（π, π）附近观察到不相称的磁峰，这与p=1/8处的磁峰相似。因此，自旋和空穴的动态条纹顺序很可能被Zn钉住，从而导致静态条纹顺序，并在x=0.21和p=1/8.3处抑制超导性。从以上结果可以看出，自旋和空穴的条纹关联存在于较宽的空穴浓度范围内，并有可能在高t_c超导性的出现中起重要作用。我们从输运测量中研究了自旋阶梯铜（Sr_<14>Cu_<24>O_<41>），得出了空穴在低温下成对而不是形成电荷密度波的结论。我们还发现由于自旋引起的热导率在该体系中异常大。

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.