Study of electronic phase transitions in composite copper oxides by intercalation

我们研究了卤素在Bi基高温超导体中的嵌入引起的各向异性(维度)、载流子浓度和超导转变温度T_c的变化，以期对高T_c超导体的机制有一定的了解。结果如下：1.我们发现实验结果可以用多层模型来解释，在多层模型中，考虑了载流子的再分布和邻近效应，将高T_c超导体视为CuO_2层(超导层)和所谓块层(正常层)的交替堆叠。尽管超导层中本征超导电性的机制尚不清楚，但电子之间的吸引势估计约为2000K。这意味着吸引势不再是由声子机制引起的，而是由相当高的能量驱动力引起的另一种机制。2.通过对Co取代的Bi2122相进行碘嵌入实验，我们发现，通过碘嵌入到Co取代的Bi2122相中，T_c的降低不仅归因于CuO_2面上空穴浓度的增加，而且还归因于CuO_2面上相邻块之间的解耦。这一结果支持上述多层模型。3.我们成功地用卤素插层法制备了Bi2222相超导。我们得出的结论是，高压氧退火对Bi2222相超导电性的出现起到的作用是为CuO_2平面提供足够的空穴载流子。

We have studied changes of the anisotropy (dimensionality), The carrier concentration and the superconducting transition temperature Tc through intercalation of halogen in the Bi-based high-Tc superconductors, in order to obtain some informations on the mechanism of high-Tc superconductivity. The results obtained are as follows.1.We have found that the experimental results are explained by the multilayr model, where a high-Tc superconductor is regarded as an alternating stack of the CuO_2 layr (superconducting layr) and the so-called block layr (normal layr), taking account of the redistribution of carriers and of the proximity effect. Although the mechanism of the intrinsic superconductivity in the superconducting layrs remains unsettles, the attractive potential between electrons is estimated as ca. 2000 K.This means that the attractive potential is expected to be no longer caused by the phonon-mediated machanism but by another machanism due to a rather high-energy driving force.2.From the experiment of iodine intercaltion into the Co-substituted Bi2122 phase, we have found that the decrease in Tc through the iodine intercalation is attributed to not only the increase of the hole concentration in the CuO_2 planes but also the decoupling between adjacent blocks of the CuO_2 planes. This result supports the above-mentioned multilayr model.3.We have succeeded in making the Bi2222 phase superconducting through halogen intercalation. We have concluded that the role of the annealing under high pressures of oxygen in the appearance of superconductivity for the Bi2222 phase is to suppply the CuO_2 planes with enough hole carriers.