Using spectroscopic techniques using synchrotron radiation such as photoemission spectroscopy and X-ray absorption spectroscopy, we are studying the electronic structures of materials to reveal the origins of the properties of those materials and to design their functionalities. To conduct state-of-the-art research, we are developing high-performance beamlines and instruments with high brightness insertion devices at the Photon Factory.
Our goal is to control and design the novel quantum phenomena appearing at the artificial structure of strongly correlated oxides by the best possible combination of the advanced analysis techniques using synchrotron radiation and sophisticated oxide growth techniques using laser molecular beam epitaxy. The wide range of properties exhibited by the strongly correlated oxides, including high-temperature superconductivity and a colossal magnetoresistance effect, makes them one of the most interesting groups of materials in condensed matter physics. The trend in the research of these strongly correlated electrons is to control them by using an artificial structure such as a quantum well structure. The novel physical properties arise from strong mutual coupling among the spin, charge, and orbital degrees of freedom in the interface region between two different oxides. Thus, in order to control the novel physical properties, it is desired to obtain the knowledge of the interfacial electronic, magnetic, and orbital structures. For this purpose, in our laboratory, we utilize state-of-the-art spectroscopic techniques, such as angle-resolved photoemission spectroscopy and dichroic X-ray absorption spectroscopy using synchrotron radiation form the Photon Factory, which enable us to probe these structures in the nm-scale region at the oxide heterointerface.
Magnetic thin films controlled at the atomic level show properties that bulk magnetic materials do not show, such as perpendicular magnetic anisotropy and a giant magnetoresistance effect. They are studied not only as so-called spintronics materials, but also from the viewpoint of basic science. It is important to know the surface and interface states of a thin magnetic film. For example, a three-layer film comprising a ferromagnet, an insulator, and a ferromagnet has an extremely large tunnel magnetoresistance effect (i.e., the tunnel resistance varies depending on magnetization of the ferromagnets). Therefore, it can be used as the read head of a magnetic recording device, and also for nonvolatile high-speed rewritable magnetic memory, the uses of which are in the implementation stage. The performance of these devices varies depending on the chemical the magnetic states of the one-atom layer of the interface between the ferromagnet and the insulator. Our goal is to learn about the surfaces and the interfaces of thin magnetic films by developing a new method of analysis such as depth-resolved X-ray magnetic circular dichroism, and to control magnetism based on the information obtained.
Kumigashira Laboratory http://oxides.kek.jp/index_e.html