The Theory of Material Design for Transition Metal Oxides

在过渡金属氧化物中，由于强的电子关联，内部的电子自由度--自旋电荷轨道发生了分离，因此，这些自由度独立地表现出来，并且相互完成。结果，出现了对称性破缺的量子态(相)。为了使材料设计成为可能，首先要建立度的序参数及其元激发的观测理论。在这个研究项目中，我们考察了观察到自旋和电荷的基元激发，即自旋和荷子的激发的可能性，并首次在一维CuO_2的角度分辨光电子能谱(APRES)实验中成功地观测到了它们。这项工作是与东京大学和斯坦福大学的实验小组合作完成的。还发展了用共振X射线散射(RXS)…观测轨道有序化的理论更多。拉曼散射实验中的元素激发。结果表明，轨道决定了过渡金属氧化物的输运性质(电荷度)和磁性(自旋度)。在La_&lt；0.88&gt；Sr_&lt；0.12&gt；MnO_3中，金属态在145&lt；T&lt；171K的温度(T)区表现出弱的铁磁性，而在145K以下，则转变为具有强铁磁性的绝缘态。结果表明，两种铁磁态和金属-绝缘体相变的发生是由轨道度数引起的：在高温下，轨道涨落诱导了熵，使金属态稳定。然而，在低温下，轨道有序化发生，能量降低。轨道有序导致了超交换作用，从而导致了较强的铁磁性。在本研究项目中，发展了过渡金属氧化物中电子自旋电荷轨道的内部自由度理论，为该化合物的材料设计奠定了基础。较少

In transition metal oxides, the separation of internal degrees of freedom of election, spin charge orbital, occurs due to the strong electron correlation, thus, the degrees behave independently and complete each other. As a result, symmetry breaking quantum states (phases) appear. Than order to make the material design possible, it is of primary importance to construct the theory of observation of the order parameters of the degrees and their elementary excitations. In this research project, we have examined the possibility of observing the elementary excitations of spin and charge, i.e., spinons and holons, and succeeded in observing them, for the first time, in the angle-resolved-photoemission spectroscopy (APRES) experiment in a one-dimensional cuprate, SrCuO_2. This work has been done in collaboration with the experimental groups in University of Tokyo and Stanford University. Also developed was the theory of observation of orbital ordering by using resonant X-ray scattering (RXS) … More . The elementary excitation in the Raman scattering experiment. It was shown that the orbital governs the transport (charge degree) and magnetic (spin degree) properties in transition metal oxides. In La_<0.88>Sr_<0.12>MnO_3, the metallic state shows weak ferromagnetism in the temperature (T) region of 145<T<171K.However, below 145K, the state changes to the insulating one with strong ferromagnetism. It was shown that the occurrences of two ferromagnetic states and metal-insulator transition are caused by the orbital degree : At high temperatures, the orbital fluctuation induces entropy and stabilizes the metallic state. However, at low temperatures, the orbital ordering occurs and the energy decreases. The orbital ordering brings about the superexchange interaction, which induces the strong ferromagnetism. The orbital ordering in this compound was detected in RXS and analyzed by using the theory mentioned above.In this research project, the theory of the internal degrees of freedom of electron, spin charge orbital, in transition metal oxides was developed and the basis of the material design was constructed. Less