钌氧化物关联电子材料的金属-绝缘体转变

项目名称： 钌氧化物关联电子材料的金属-绝缘体转变

项目编号： No.10874213

项目类型： 面上项目

立项/批准年度： 2009

项目学科： 轻工业、手工业

项目作者： 郑萍

作者单位： 中国科学院物理研究所

项目金额： 43万元

中文摘要： 本课题中我们主要进行了烧绿石结构的钌氧化物(A2Ru2O7)的样品制备,并与徐刚石友国合作在国际上首次对很难合成的Ca2Os2O7的金属-绝缘体相变的性质和机理进行了研究，结合磁化率、比热和红外反射率谱测量手段探测分析了局域电子自旋的自旋态及磁有序状态和d能带提供的巡游电子间的库伦排斥能在金属-绝缘体转变中的作用，观测到了直接能隙打开的过程和能量大小。理论计算发现这是Os 5d电子间的库伦排斥能和Os 的非共线反铁磁作用能共同作用的结果，是一特异的Mott绝缘体。结合国际前沿的发展，作为课题的延伸我们还制备了3d金属氧化物的单晶/多晶，通过输运性质的测量和分析，我们首次将由于磁场中电子螺旋运动能量量子化而导致费米面变化对磁阻的贡献的模型运用到SDW材料，为区分该材料中的SDW的起源是巡游电子自旋还是铁离子的局域磁矩之间的相互作用从电子输运性质的角度提供了一个实验依据。还研究了SDW在光电导谱上的反映。在SCI收录的杂志上发表论文2篇，待发表1篇。根据研究的需要，结合商用PPMS开发出分辨率为万分之五的高灵敏度差分比测量系统选件，为国际唯一。由于是选件，可以提高仪器使用率。

中文关键词： Ru氧化物;光电导谱;电子关联;金属-绝缘体转变

英文摘要： In this project, we have done effort to prepare the Ru-oxides but no good sample was obtained. Later the Mott insulating state was observed in Sr2IrO4 and evoked great interest studying. We coorperated with our colleague Yooguo Shi and Gang Xu to investigete the physiccs properties and mechanism of the metal-insulator transition in 5d oxides Ca2Os2O7, which was discovered in resistivity but no further study before. The phase transition was revealed by our specific heat, magnetization and the optical reflectance investigations. The spin magnetic state and the entropy change caused by the phase transition were studied by the mantization and specific heat analysis. A direct energy gap was observed developing with temperature decreasing in the optical measurements. Theoretical calculation showed that the direct gap opened only when the intra-atomic Coulomb repulsion combines with the non-collinear antiferromagnetic correlation (similar to Slater type) for Os (4c) 5d bands while for the narrower Os(4b) bands the intraatomic Coulomb repulsion of 5d electrons was considered. Therefore this is the other novel Mott insulator in 5d oxides. Moreover, following the development of the condensed physics, we prepared some good single crystals of 3d metal oxides and payed some attention to the effect of the spins correlation on their transition properties. The large magnetoresistances of SrFe2As2 and BaFe2As2 in the magnetic ordered state are observed and studied in the field with different applied directors. The data in the magnetic ordered state was found to be reasonably described by a modified two-band galvanomagnetic model including the enhancement effect of the applied magnetic field on the spin-density-wave gap. The field enhanced spin-density-wave gaps for different types of carriers are different. On the other hand we have studied the spin density wave effect on the optical spectra revealed by other FeAs material. By now, two papers are published in the jounals included in SCI, one is to be submitted. A highly sensitive diffraction specfic heat measuremental system combined with PPMS was designed, built, adjusted and now was tried in part of the above studies. Its accuracy is about 0.05% in 20K<T<200K.

英文关键词： Ru-oxides;optical spectroscopy;electron correlation;Metal-insulator transition