| Co-Investigator(Kenkyū-buntansha) |
KOSHIBAE Wataru Institute for Materials Research, TOHOKU UNIVERSITY, Research Associate, 金属材料研究所, 助手 (20273253)
ISHIHARA Sumio Institute for Materials Research, TOHOKU UNIVERSITY, Research Associate, 金属材料研究所, 助手 (30292262)
TOHYAMA Takami Institute for Materials Research, TOHOKU UNIVERSITY, Associate Professor, 金属材料研究所, 助教授 (70237056)
TAKAHASHI Saburo Institute for Materials Research, TOHOKU UNIVERSITY, Research Associate, 金属材料研究所, 助手 (60171485)
KOYAMA Tomio Institute for Materials Research, TOHOKU UNIVERSITY, Research Associate, 金属材料研究所, 助手 (30153696)
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| Research Abstract |
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)
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. 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
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