Charge and Spin Coupling in 3d-Transition-Metal Oxides with Perovskite-Related Structures

点击翻译按钮获取中文摘要

The present research aimed to elucidate the charge dynamics of doped holes in a series of 3d-transition-metal oxides with perovskite-related structures. These oxides are basically antiferromagnetic insulators. We demonstrate by the potical spectroscopy that as the spin system is diluted or the long-range spin order is frustrated by the doped holes, the spectral weight is transferred from high-energy to low-energy region. The low-energy excitations form a so-called mid-IR absorption band which is generic to all 3d-transition-metal oxides doped with holes. The intensity of the mid-IR band is connected with the local spin order. The close connection between the spin system and the charge dynamics is most vividly displayd in the high-T_c Cu oxides owing to strong spin fluctuations in two dimensions. The research has been extended to one-dimensional Ni and Cu oxides in which some quantum spin fluid is formed even in a parent insulator due to much stronger spin fluctuations in one dimension. The presence of quantum spin fluid has been confirmed by muSR experiment for Y_2BaNiO_5, and hole doping into this compound has been successfully done, though the compound remains to be insulating. The result and strategy developed in the present research will provide a basis for future study of the charge dynamics in doped quantum spin fluid.