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

最近，各种研究人员已经明确指出，以d电子或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，因为红外光子很低，因此可以在固体中实现极低能量的光激发。本研究的目的是在实验上探测E_F附近电子结构的变化，并弄清它与各种物理性质产生的机制之间的关系。然而，大多数有趣的材料生长在非常小的单晶态或具有表面粗糙度的多晶态。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。除了观察到温度诱导的金属绝缘体相变外，我们还利用SPEING-8对YBS进行了这样的实验。本研究取得了以下研究成果：(1)d电子化合物的温度诱导金属-绝缘体转变研究。CuIr_2S_4及其相关化合物。(2)YBS高压红外显微测量的性能。(3)与稀土单硫化物Rex(Re=Yb，X=S和Te)和单烟碱Rex(Re=La，Ce，X=Sb)有关的高质量单晶的晶体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.