OPTICAL SPECTRUM OF STRONGLY CORRELATED ELECTRON SYSTEMS

红外光谱是研究具有强电子关联的材料电子结构的一种非常有用的方法，因为它具有很低的光子能量，从而使固体中低能的光激发成为可能。然而，大多数有趣的材料生长在非常小的单晶线状态或具有一定粗糙度的多晶态。因此，用这种样品进行红外光谱测量是困难的。在这种情况下，红外显微测量似乎工作得很好，因为显微镜使用非常小的样品测量光谱成为可能。我们利用红外显微镜结合红外干涉仪(Bruker 66V)对这些材料进行了从远红外到紫外极宽能区的反射和透射率测量。在本研究中，通过对TmTe和SmTe这两种在红外区具有较小能隙的半导体进行透射率测量，我们发现TmTe在150 meV的吸收边具有特征的吸收结构。另一方面，SmTe显示出简单的吸收边。虽然两种材料在费米能级附近的电子结构不同，但它们的电子组态非常相似。(2)YBB_&lt；12&gt；是一种典型的近藤绝缘体，只有在较低的温度下才能形成较小的能隙。通过对Yb_t；1-x&gt；Lu_xB_&lt；12&gt；单晶的反射率精度在1%以内的反射测量发现，在低温下，Yb对非磁性Lu的逐渐取代使Ybb_&lt；12&gt；单晶的带隙中出现了一个新的能带。(3)红外显微测量对于研究强关联电子系统的电子结构是非常有效的。

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.