Anomolous Charge Transfer in High-Tc Superconducting Oxides Probed by Raman Scattering

铜基高温超导氧化物的超导电性与载流子掺杂到母体绝缘体引起的绝缘体到金属的转变密切相关。在本研究中，拉曼散射被用作监测由原子替代(掺杂)引起的绝缘体-金属相变附近的电荷转移和电荷再分布的工具。所选择的体系包括Bi2Sr2Ca1-xYxCu2O8d(x=0-1)，并在一些定义良好的单晶和多晶样品中研究了它们的拉曼光谱。从偏振和Y掺杂的依赖关系出发；通过与以前关于铋系铜酸盐的报道的比较，我们首次明确地确定了理想的体心四方晶胞中拉曼允许的7个模的模式分配。例如，在TH…中解决了630 cm-1和460 cm-1附近两个最突出的拉曼频带的指定的混淆问题进一步研究了单晶偏振拉曼光谱，包括困难的c轴偏振几何结构。更令人兴奋的结果是，CuO_2面上空穴载流子数目减少的直接证据是从与CuO_2面上振动有关的声子模的强度变化中提取出来的：即，随着Y掺杂的增加，涉及CuO_2面上原子的振动模的强度迅速增加，这是由于在空穴减少的Y掺杂样品中金属屏蔽减少的结果。在几乎所有已知的具有不同空穴浓度的高T_c超导氧化物中都发现了相似的强度变化。我们提出，可以通过测量CuO_2平面的拉曼强度来估计给定超导样品的空穴浓度(从而超导转变温度T_c)。在本研究过程中，我们还发现了耗氧的Y基高T_c超导体在可见光照射下在室温下发生的异常相变(光致相变)，这可能为未来的工业应用开辟新的机会。较少

The superconductivity in copper-based high-Tc superconducting oxides is intimately linked with the insulator-to-metal transitions, which are induced by carrier doping into the parent insulator. In this study, Raman scattering has been used as a tool to monitor the charge transfer and charge redistribution near the insulator-to-metal transitions induced by atomic substitutions (doping). The system chosen for the study includes Bi2Sr2Ca1-xYxCu2O8+d (x=0-1), and thier Raman spectra have been investigated in a number of well-defined single crystal and polycrystalline samples. From the polarization and Y-doping dependence ; and from a comparison with previous reports on Bi-based cuprates, we have for the first time established clearly mode assignments of the 7 modes that are Raman allowed within the ideal body-centered tetragonal unit-cell. For instance, confusions of the assignments for the two most prominent Raman bands around 630 cm-1 and 460 cm-1 have been solved without ambiguity in th … More is study by the single-crystal polarized Raman measurements including the difficult c-axis polarized geometry. A more exciting result in this study was that the direct evidence for a decreased number of hole carriers onto the CuO2 planes was extracted from the change in intensities of phonon modes associated with CuO2 plane vibrations : i.e.with increasing Y doping we find that the vibrational modes involving atoms in the CuO2 planes rapidly increase in intensity as a result of the reduced metallic screening in the hole-depleted Y doped samples. Similar intensity variations have been found in almost all the known high-Tc superconducting oxides with different hole concentration. We have proposed that the hole concentration of a given superconducting sample (thereby superconducting transition temperature Tc) can be estimated by measuring the Raman intensity of the CuO2 plane. During the course of this study, we have also discovered in oxygen depleted Y-based high-Tc superconductors unusual phase transitions at room temperature induced by visible light irradiations (photoinduced phase transition), which may open up new opportunities for future industrial applications. Less