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绝缘体-金属转变密切相关，这是由载流子掺杂到母体绝缘体中引起的。在这项研究中，拉曼散射已被用来作为一种工具来监测附近的绝缘体到金属的原子取代（掺杂）引起的转变的电荷转移和电荷再分布。所选系统包括Bi_2Sr_2Ca_（1-x）Y_xCu_2 O_（8 +d）（x=0-1），并在一些定义明确的单晶和多晶样品中研究了它们的拉曼光谱。从偏振和Y掺杂的依赖性，并从与以前的报告的Bi基铜酸盐的比较，我们已经为第一次建立了明确的模式分配的7个模式，拉曼允许在理想的体心四面体晶胞。例如，在630 cm-1和460 cm-1附近的两个最突出的拉曼带的分配的混淆已经在没有歧义的情况下解决。 关于我们 通过单晶偏振拉曼测量研究了晶体的c轴偏振几何。本研究中更令人兴奋的结果是，从与CuO 2平面振动相关的声子模式强度变化中提取了CuO 2平面上空穴载流子数量减少的直接证据：即，随着Y掺杂的增加，我们发现，由于孔中金属屏蔽的减少，涉及CuO 2平面中原子的振动模式的强度迅速增加。耗尽Y掺杂样品。在几乎所有已知的具有不同空穴浓度的高温超导氧化物中，都发现了类似的强度变化。我们已经提出，一个给定的超导样品的空穴浓度（从而超导转变温度Tc）可以通过测量的拉曼强度的CuO 2平面估计。在本研究过程中，我们还发现在氧耗尽的Y基高Tc超导体中，在室温下由可见光照射引起的不寻常的相变（光致相变），这可能为未来的工业应用开辟新的机会。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