Study on the electronic structure in the vicinity of the Fermi level of strongly correlated electron system by very low energy photo-excitation

近年来，各种研究人员已经明确了以d-或f-电子化合物为代表的强相关电子系统的物理性质是由材料在费米能级（E_F）附近的电子结构的微小变化产生的。红外光谱研究是研究这类材料电子结构的一种非常有用的方法，因为红外光子非常低，从而使固体中的极低能量光激发成为可能。本研究计划的目的是通过实验检测非常接近E_F的电子结构的变化，并弄清各种物理性质的产生与机理的关系。然而，大多数令人感兴趣的材料生长在非常小的单晶状态或表面粗糙的多晶状态。因此，用这种样品进行红外光谱测量是困难的。第二个目的是提高红外显微测量的性能，使微小样品的光谱测量成为可能。除了观察温度诱导的金属绝缘体转变外，我们还利用SPring-8在YbS上进行了此类实验。在本研究中，得到以下结果：(1) d电子化合物上温度诱导金属-绝缘体跃迁的研究。CuIr_2S_4及其相关化合物。(2) SPring-8高压下红外显微测量YbS的性能。(3)稀土单硫系化合物ReX （Re=Yb， X=S和Te）和单硫系化合物ReX （Re=La, Ce， X=Sb）的高质量单晶生长及基本物理性质的测定。

Recently it has been make clear by various kinds of researchers that the physical properties of strongly correlated electron system represented by d- or f-electron compounds is generated by the minute change in the electronic structure in the vicinity of the Fermi energy level (E_F) of the materials. Infrared (IR) spectroscopic study is very useful method to investigate the electronic structure of this kind of materials because IR photon is very low and therefore it makes possible the very low energy optical excitation in the solids. The purpose of this research program is to detect experimentally the change in the electronic structure very close to the E_F and to make clear the relation with the mechanism of the generation of the various physical properties. However, most of interesting materials grow in a very small single crystalline state or in polycrystalline state with surface roughness. Therefore it is difficult to perform IR spectroscopic measurement with such specimens. Then the second purpose is to performance of IR microscopic measurement which makes possible the measurement of the optical spectrum with a very tiny specimens. We performed such experiments on YbS by using SPring-8 in addition to the observation of the temperature-induced metal insulator transition. In this study, the following results were obtained.(1) Study of temperature-induced metal-insulator transition on d-electron compounds. CuIr_2S_4 and its related compounds.(2) Performance of the IR microscopic measurement under high pressure on YbS at SPring-8.(3) Crystal growing of high quality single crystals related rare earth monocalcogenides, ReX (Re=Yb, X=S and Te) and monopnictides, ReX (Re=La, Ce, X=Sb), and the measurements of the fundamental physical properties.