Study of electronic phase transitions in composite copper oxides by intercalation

本文研究了Bi系高温超导体中卤素嵌入后各向异性（维数）、载流子浓度和超导转变温度Tc的变化，以期获得有关高温超导机理的一些信息。结果表明：1.我们发现，实验结果可用多层模型来解释，即把高温超导体看作是CuO_2层（超导层）和所谓的块层（正常层）的交替叠层，考虑了载流子的再分布和邻近效应。尽管超导层中本征超导电性的机制尚未确定，但电子之间的吸引势估计为约。这意味着吸引势不再是由声子介导的机制引起的，而是由另一种机制引起的，这种机制是由一种相当高的能量驱动力引起的。我们发现，通过碘的插入，Tc的降低不仅归因于CuO中空穴浓度的增加，2面之间的耦合，而且CuO_2面相邻块体之间的耦合也是不耦合的。这一结果支持了上述的多层模型。3.我们成功地通过卤素的嵌入使Bi_（2222）相超导化。我们得出结论，高压氧退火对Bi_（2222）相超导电性的作用是为CuO_2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.