Study of electronic inhomogeneity and superconductivity in high-Tc superconductors by scanning tunneling microscopy.

本项目旨在利用扫描隧道显微镜（STM/STS）揭示高tc氧化物超导体的原子尺度电子结构，并研究超导性与超导区和赝隙区组成的颗粒结构等特征电子结构之间的关系。在本研究中，我们观察到了不同载流子浓度的YBa2Cu3Oy （YBCO）和Bi2-xPbxSr2CuOy （Pbx-Bi2201）单晶的原子尺度电子结构以及宏观超导性能。YBa2Cu3Oy:(1)我们在氮气气氛中通过控制退火条件成功制备了相邻CuO2层之间具有不同电子耦合强度的单晶，并观察到了涡旋系统的二维到三维转变。(2)从宏观和微观研究了氧缺陷和杂质对涡流结构和电子态的影响。(3)在低偏置电压下，BaO层沿Cu-O方向有更多的电子调制。这些调制与杂质和/或缺陷引起的电子不均匀性密切相关。(1)研究了制备好的Pb取代Bi2201单晶的超导转变温度Tc和赝隙形成温度T^*与温度和载流子浓度的关系。(2)明确了赝隙存在两种类型；一个与超导的前驱效应有关，另一个与强电子相关性有关。后者甚至存在于过掺杂区域。(3)在高于300 mV的高偏置电压下测量的STM图像中，观察到由Bi和Pb原子组成的清晰的二维原子排列。另一方面，在低于150 mV的低偏置电压下，已经发现对比密度形成直径为1-3 nm的明亮斑块。这些结果与在Bi2212中观察到的电子粒度一致。少

The aim of this program is to reveal atomic-scale electronic structures of high-Tc oxide superconductors by scanning tunneling microscopy (STM/STS) and to investigate the relationship between the superconductivity and the characteristic electronic structure, such as granular structure composed of the superconducting and pseudogap regions. In this study, we have observed atomic-scale electronic structures of YBa2Cu3Oy (YBCO) and Bi2-xPbxSr2CuOy (Pbx-Bi2201) single crystals with various carrier concentrations as well as macroscopic superconducting properties.1. YBa2Cu3Oy : (1) We have successfully prepared single crystals with different electronic coupling strength between adjacent CuO2 layers by controlling anneal conditions in nitrogen atmosphere and observed 2 to 3 dimensional transformation of the vortex system. (2) Effects of oxygen defects and impurities on the vortex structure and the electronic state have been studied macroscopically and microscopically. (3) One-dimensional elect … More ronic modulations on the BaO layer at low bias voltage have been observed along the Cu-O direction. These modulations are closely related to the electronic inhomogeneity induced by impurities and/or defects.2. Bi2-xPbxSr2CuOy : (1) The temperature and carrier concentration dependences of the superconducting transition temperature Tc and the pseudogap formation temperature T^* have been studied for well prepared Pb substituted Bi2201 single crystals. (2) It has been clarified that there exist two types of pseudogap ; one is related to a precursor effect of superconductivity and another to a strong electron correlation. The latter exist even in the overdoped region. (3) In STM images measured at high bias-voltages above 300 mV, a clear two-dimensional atomic arrangement, which consists of Bi and Pb atoms, has been observed. On the other hand, at low bias-voltages below 150 mV, it has been found that a contrasting density forms into bright patches of 1-3 nm diameters. These results are consistent with the electronic granularity observed in Bi2212. Less