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Direct Observation of Cu-O Plane by STM and Local Pair-breaking Effect on High-T_c Superconductor

Cu-O面的STM直接观测及高温超导体局部断对效应

基本信息

批准号：
10440095
负责人：
IDO Masayuki
金额：
$ 5.44万
依托单位：
HOKKAIDO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B).
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 2000
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-10440095/
关键词：
High-Tc Cuprates STM CuO plane Impurity Effect Pseudo Gap 超伝導ギャップ超伝導不純物効果

项目摘要

We observed the atomic image of the Cu-O plane of Bi2212 using STM technique. The atomic image of the Cu-O plane for over-doped samples is characterized by cross-striped pattern, implying that the orbit of carriers will result from a strong hybridization of Cu-3d and O-2p orbits. On the other hand, transport and magnetic properties of under-doped (UD) samples indicate that the hybridization of Cu-3d and O-2p orbits will be rather suppressed as doping level is reduced. Therefore, we can expect that the Cu-O atomic image of STM is changed into a simple array of circles in the UD region. However, we could not confirm such a change of the atomic STM image because we failed to prepare UD single crystals of high quality. In the present study, we also studied impurity effects of nonmagnetic Zn- and magnetic Ni-ions on the superconductivity of La214. We found that the superconductivity is locally suppressed over the region where magnetic correlation developed on the Cu 3d-spin network is disturbed by Zn ions. This is the reason why nonmagnetic Zn-ions cause strong local pair-breaking effect compared with magnetic Ni-ions, and implies that the Cu 3d-spin network will play a crucial role in causing the high-Tc superconductivity. It was also found that the pseudo-gap state begins to develop gradually around the mean-field temperature T^* (〜2Δ_O/4.3k_B) and is easily suppressed by doping impurities. The dependence of T^* on impurity concentration is very similar to that of Tc, indicating that the pseudo-gap is closely related with the high-Tc superconductivity, as expected.

我们用STM技术观察了Bi 2212的Cu-O面的原子像。过掺杂样品的Cu-O面的原子图像具有交叉条纹图案的特征，这意味着载流子的轨道将由Cu-3d和O-2 p轨道的强杂化产生。另一方面，欠掺杂（UD）样品的输运和磁性表明，随着掺杂水平的降低，Cu-3d和O-2 p轨道的杂化将受到抑制。因此，我们可以预期STM的Cu-O原子图像在UD区域被改变为简单的圆阵列。然而，我们无法确认原子STM图像的这种变化，因为我们未能制备高质量的UD单晶。在本研究中，我们还研究了杂质Zn-和磁性Ni-离子对La 214超导电性的影响。我们发现，超导电性被局部抑制的区域上的Cu 3d自旋网络上的磁关联被Zn离子干扰。这就是为什么Cu ~（2+）Zn ~（2+）离子比磁性Ni ~（2+）离子具有更强的局域对破缺效应的原因，同时也暗示了Cu ~（2+）的3d自旋网络在高温超导中起着至关重要的作用。在平均场温度T^*（Δ 2Δ O/4.3kB）附近，赝能隙态开始逐渐发展，并容易被掺杂抑制。T^* 对杂质浓度的依赖关系与Tc非常相似，表明赝能隙与高Tc超导电性密切相关。