OPTICAL SPECTRUM OF STRONGLY CORRELATED ELECTRON SYSTEMS

红外光谱研究是研究强电子相关材料的电子结构的一种非常有用的方法，因为它具有非常低的光子能量，从而使固体中的低能光激发成为可能。然而，大多数有趣的材料生长在非常小的单晶线状态或多晶状态，具有一定的粗糙度。因此，用这种样品进行红外光谱测量是困难的。在这种情况下，红外显微测量似乎工作得很好，因为显微镜可以用非常微小的样品测量光谱。利用红外显微镜结合布鲁克66v红外干涉仪，在远红外到紫外的极宽能量区对这些材料进行了反射和透射测量。在本研究中，得到了以下结果：(1)通过对同为红外区小能隙半导体的TmTe和SmTe的透射率测量，我们发现TmTe在150meV处的吸收边缘具有特征吸收结构。另一方面，SmTe表现出简单的吸收边。虽然两种材料的电子组态非常相似，但接近费米能级的电子结构却不同。(2) YbB_<12>是典型的近藤绝缘子，只有在低温时才能形成小能隙。对Yb_<1-x>Lu_xB_<12>单晶的反射率进行了精度在1%以内的反射测量，发现在低温条件下，非磁性Lu逐渐被Yb取代，在YbB_<12>的带隙中出现了一个新的带。(3)红外显微测量在强相关电子体系的电子结构研究中是非常有效的。

Infrared (IR) spectroscopic study is very useful method to investigate the electronic structure of materials with strong electron correlation because its has a very low photon energy and therefore it makes possible the low energy optical excitation in the solids. However, most of interesting materials grow in a very small single crystal-line state or in polycrystalline state with definite roughness. Therefore it is difficult to perform IR spectroscopic measurement with such specimens. In such a case, IR microscopic measurement seems to work well because, of microscope makes it possible to measure optical spectrum with a very tiny specimens. We performed reflection and transmission measurements on these materials by using IR microscope combined with IR interferometer (Bruker 66v) in the very wide energy region from far-infrared to ultraviolet.In this study, the following results were obtained,(1) From the transmission measurement on TmTe and SmTe which are both a semiconductor with a small energy gap in the IR region, we found that TmTe has a characteristic absorption structure at 150meV in the absorption edge. On the other hand, SmTe showed a simple absorption edge. The electronic structure close to the fermi level are different from each other althpough the electron configuration of both materials are very similar.(2) YbB_<12> is recognized as a typical Kondo-insulator which exhibits a formation of small energy gap only at low temperature. From the reflection measurement with an accuracy within 1% in the reflectivity on Yb_<1-x>Lu_xB_<12> single crystal, we foud that the gradual substitution of non-magnetic Lu with Yb gives rise to an appearance of a new band in the band gap in YbB_<12> at low temperature.(3) IR microscopic measurement was confirmed to be very effective in the study of the electronic structure of strongly correlated electron systems.