講座

X線分光の現在
V.　 共鳴X線散乱

Modern X-ray Spectroscopy
V.　 Resonant X-ray Scattering

村上洋一
Youichi MURAKAMI

放射光X線を利用した共鳴X線散乱法は，精密な電荷分布や磁気密度分布を調べる手法として発達してきたが，最近では強相関電子系に適用され，多くの成果を挙げている．本稿ではまず，共鳴X線散乱の散乱断面積を物質中の電子と電磁波の相互作用から導出し，その散乱振幅がスカラーではなくテンソルとして書かれることを示す．本手法を用いた具体例として，マンガン酸化物の電荷・軌道秩序の観測例を紹介した後，本手法の最近の発展と将来の展望を簡単に述べる．

Resonant x-ray scattering (RXS) is a very powerful technique to detect the charge distribution and magnetization density with a synchrotron radiation source. Recently this technique has been applied to study charge-, spin-, and orbital-orderings in strongly correlated electron systems. In this paper the cross section and the scattering amplitude of RXS are given on the basis of the interaction between electrons in matter and electromagnetic wave. The atomic scattering factor becomes a tensor instead of a scalar through the resonant process. Charge and orbital orderings of perovskite manganites have been studied using the RXS technique. It is shown that the RXS intensities have characteristics in energy, polarization, and azimuthal angle dependences. Finally an outlook for the RXS technique is briefly mentioned.

Keywords: resonant x-ray scattering, charge ordering, orbital ordering