the search of the orbital ordering of the magnetic moment by using x-ray magnetic scattering

我们研究了“高温超导性”和/或“巨磁电阻（CMR）”作为强相关电子系统的关键现象。为了探索这一重要问题，我们开始利用同步加速器x射线散射的新技术，在中子散射的基础上，研究一种新的“有序”自由度。首先，我们仔细研究了磁性金属元素（实际上是Mn阳离子）K边能量处发生轨道阶x射线共振散射的机理。然后我们发现了4p轨道与处于轨道有序态的3d轨道之间的库仑相互作用提升4p简并度的机理。然后它产生增强或共振。然后利用新建立的同步x射线散射技术，深入研究了由Jahn Teller效应引起的LaMnO_3的轨道序。其次，我们还将这一技术扩展到作为公认的CMR材料的掺杂锰的金属绝缘体的相变研究。我们发现相变是由轨道有序-无序转变引发的。第三，我们将近两年研究的项目扩展为一个新的项目，目标是研究轨道波动的标准探针。

We have studied the "high temperature superconductivity " and /or "colossal magnetoresistance (CMR)" as the key phenomena in the strongly correlated electron systems. In order to explore this important issue, we initiated to investigate a novel degree of freedom of "order" by using new technique of the synchrotron x-ray scattering besides neutron scattering.First we studied carefully the mechanism of the resonant x-ray scattering of the orbital order occurred at the energy of K edge of the magnetic metal element, actually Mn cations. Then we found the mechanism that the intra Coulomb interaction between 4p and 3d orbital which is in the orbital ordered state lifts the 4p degeneracy. Then it gives rise an enhancement or resonance. Then we deeply studied the orbital order in LaMnO_3 originated by the Jahn Teller effect by using this newly established technique of the synchrotron x-ray scattering.Second, we also extend this technique to study the phase transition of metal insulator in the doped manganites as recognized the CMR materials. We found that the phase transition is triggered by the orbital order-disorder transition.Third, we extend this project studied during the recent two years granted to a new project aiming the standard probe of studying the orbital fluctuations.