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Theoretical Studies on Electronic State and Superconductivity in Oxide Superconductors

氧化物超导体电子态与超导性的理论研究

基本信息

批准号：
01540289
负责人：
TACHIKI Masashi
金额：
$ 0.9万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1989
资助国家：
日本
起止时间：
1989 至 1990
项目状态：
已结题

项目摘要

The superconductivity in the oxide superconductors appears only in the metallic region close to the metalinsulator transition, and to clarify the properties of electronic states around this region is considered one as of the keys to understand the mechanism of the high-T_c superconductivity. We calculated the electronic density of states selfconsistently by use of the d-p mixing model among Cu-orbits and O-orbits, including many body effects induced by spin and charge fluctuations. We have found that new states are formed inside the charge transfer insulator gap with carrier doping due to many body effects. The obtained results explain qualitatively the experimental results of spectral intensity of photoemission and optical conductivity. We published these results in 14 papers. The theoretically obtained new states at the Fermi level are expected to include large charge fluctuation. A possibility for such fluctuation to work as an attractive force in the mechanism of the superconductiv … More ity is under investigation at present.Due to their layered structures, cuprate oxide superconductors also show various anomalous electronic and magnetic properties in the superconducting state. We have proposed the model in which the high-T_c superconductivity appears primarily in the CuO_2 planes by certain attractive force and superconductivity on the other layers is induced by the proximity effect. From this model, we calculated tunneling conductance, anisotropy of the optical conductivity, Knight shift and nuclear magnetic relaxation rates of ions on various layers. Variety in appearance of physical quantities in the experimental observation can be understood in a unified way by use of our model. Structure of flux line in the above mentioned model are expected to be very anisotropic. We predicted the intrinsic pinning effect and anomalous behaviors of magnetization curves. These results are published in 14 papers. A part of the above results was presented in the invited talks at the 19-th international conference of low temperature physics in Brighton, England. Less

氧化物超导体中的超导性只出现在靠近金属绝缘体转变的金属区域，阐明该区域周围电子态的性质被认为是理解高温超导机理的关键之一。我们利用Cu轨道和O轨道之间的d-p混合模型自洽地计算了电子态密度，包括许多由自旋和电荷波动引起的体效应。我们发现，由于许多体效应，载流子掺杂在电荷转移绝缘体间隙内形成了新的态。所得结果定性地解释了光电发射光谱强度和光导率的实验结果。我们在 14 篇论文中发表了这些结果。理论上在费米能级获得的新状态预计将包括大的电荷波动。这种波动在超导机制中作为吸引力的可能性目前正在研究中。由于其层状结构，铜氧化物超导体在超导状态下也表现出各种反常的电子和磁性特性。我们提出了高温超导模型，其中高温超导主要出现在CuO_2平面上，由于一定的吸引力，而其他层上的超导是由邻近效应引起的。根据该模型，我们计算了各层离子的隧道电导、光导率各向异性、奈特位移和核磁弛豫率。通过使用我们的模型，可以以统一的方式理解实验观察中物理量表现的变化。上述模型中的通量线结构预计具有很大的各向异性。我们预测了磁化曲线的内在钉扎效应和异常行为。这些结果发表在 14 篇论文中。上述部分成果在英国布莱顿举行的第19届国际低温物理会议的特邀报告中发表。较少的