第277回物性セミナー(4研究科共同セミナー:6月1日)



題目:Ab initio Calculations as a Tool for Discovery:

   Charge-orbital Ordering and Verwey Transition in Magnetite



講師:Prof. Guang-Yu Guo 氏

(Department of Physics, National Taiwan University,Taipei 106, Taiwan )



日時:2006年6月1日(木)16:30〜

場所:先端科学総合研究棟 405N講義室



講演要旨

Today, ab initio calculations have become indispensable in materials research. In particular, they are essential to understand the intricate phenomena occurring in materials, to search for new materials and to design the materials with desired properties. In this talk, I will report how our recent ab initio calculations [1]lead to the discovery of a sophisticated t2g-orbital ordering in magnetite (Fe3O4) which helps to resolve a 60 year old fundamental problem in solid state physics. In the past ten years, there has been considerable interest in charge ordering in transition metal oxides because the electric transport and magnetic properties of transition-metal oxides are intimately related to charge ordering.

For example, dynamic fluctuations of charge ordered stripes have been proposed as a mechanism of high temperature superconductivity. The classic charge ordering problem is, however, that of magnetite (Fe3O4), which was first proposed by Verwey in early 1940・s in order to explain the observed metal-insulator (M-I) transition in the system. However, despite of intensive experimental and theoretical investigations in the past six decades, the origin and mechanism of the charge ordering and hence Verwey transition have remained a mystery and have fascinated generations of solid state physicists ever since. Our ab initio calculations reveal that magnetite forms an insulating charge-orbital ordered state below the Verwey transition temperature. More importantly, we find an associated t2g-orbital ordering on the octahedral Fe2+ sublattice. This finding resolves such fundamental issues about the Verwey transition as the mechanism for the charge ordering and for the formation of the insulating gap, as well as the nonobedience of the Anderson・s criterion for the charge ordering.

Finally, the predicted t2g-orbital ordering in magnetite has recently been observed in resonant x-ray scattering experiments [2].





       −4研究科共同セミナーの認定科目です−

        −後援 先進物質機能研究センター−



本セミナーの担当: 小口多美夫(先端研)内線7015





物性セミナー世話人:高根 美武(内7653) 浴野 稔一(内6552)

          中村 文彦(内7042) 木村 昭夫(内7471)

          犬丸  啓(内7741)





     広報担当:伊賀文俊(内7026)


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