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，各种研究者已经明确，以d-或f-电子化合物为代表的强关联电子系统的物理性质是由材料费米能级（E_F）附近电子结构的微小变化所产生的。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，这使得固体中的低能光激发成为可能。本研究计划的目的是在实验上探测与E_F非常接近的电子结构的变化，并弄清其与各种物理性质产生机制的关系。然而，大多数感兴趣的材料生长在一个非常小的单晶状态或多晶状态与表面粗糙度。因此，很难用这样的样品进行红外光谱测量。第二个目的是进行红外显微测量，这使得用非常小的样品测量光谱成为可能。我们进行了这样的实验YbS通过使用SPring-8除了观察温度诱导的金属绝缘体转变。在这项研究中，获得了以下结果。(1)d电子化合物温度诱导金属-绝缘体转变的研究。CuIr_2S_4及其相关化合物。(2)在SPring-8高压下对YbS的红外显微测量的性能。(3)高质量的稀土单硫族化合物雷克斯（Re=Yb，X=S和Te）和铌族化合物雷克斯（Re=La，Ce，X=Sb）单晶的生长和基本物理性质的测量。

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.