Rich phases and gigantic response of correlated electrons
Professor Yoshinori Tokura, Department of Applied Physics, University of Tokyo, Japan

Professor Yoshinori Tokura received his PhD in Applied Physics from University of Tokyo in 1981. Since 1994, he has been Professor in Department of Physics, and then in Department of Applied Physics, University of Tokyo. His interests are in correlated electron science (exploratory materials, electronic properties, and optics) of transition-metal compounds and organic materials. He is concurrently Director of Correlated Electron Research Center, AIST, Japan.

Presentation (2383kb)

Transition-metal oxides offer an intriguing playground to find amazing electronic property/functionality, such as high-temperature superconductivity in copper-oxides and colossal magnetoresistance in manganese-oxides. In those materials, a vast number of electrons, comparable to the number of the constituent atoms, are strongly interacting with each other and tend to lose their mobility. Such a particle nature of electrons, contrary to the cases of conventional metals and semiconductors, can activate the internal degrees of freedom of an electron charge, spin, and orbital (electron's probability-density distribution). These correlated electrons, when placed on the specific topological atomic lattice, may form the rich and complex phases or the self-organized structures. Those are, for example, charge-spin stripes, charge-orbital ordered states, and liquid-crystal like states with anisotropic charge-spin-orbital correlations.

Here some examples are presented for the correlated-electron's ordering patterns and it is shown how dramatically they can respond to external stimuli (inputs), say to electric/magnetic fields, light, and pressure. In particular, the response of correlated electrons can be huge and fast in the vicinity of the boundary of the competing electronic phases. Importantly, reflecting the regained particle-nature of electrons, the gigantic response can be robust to down-sizing of the material form to nano-scale and hence be promising for future applications.