RuAs各向异性金属-绝缘体转变的光学和光电研究
Optical and photoelectrical studies on anisotropic metal-insulator transition of RuAs
摘要：
利用偏振光学电导[ $σ(ω)$ ]谱、角积分光电子谱和局域密度近似能带计算，研究了金属-绝缘体相变（MIT）材料RuAs两步相变时电子结构的各向异性变化.无论是高温相还是低温相的PE谱和$σ(ω)$谱，以及由MIT引起的能隙的形成，都与LDA能带计算结果基本一致，因此高温相和低温相的基本电子结构可以在没有电子关联的情况下得到解释.然而，在HT和LT相之间的中间相的电子结构尚未澄清。极化的$σ(ω)$光谱不仅揭示了各向异性能隙的形成，而且还揭示了各向异性的间隙打开温度，即，HT相中沿$c$轴的能隙在较高转变温度附近开始打开，而沿$b$轴的能隙在较低转变温度以下打开。这一发现表明，两步MIT起源于各向异性能隙的形成。
英文摘要：
The anisotropic changes in the electronic structure of a metal-to-insulator transition (MIT) material, RuAs, with two-step phase transition are reported by using polarized optical conductivity [$σ(ω)$] spectra, angle-integrated photoelectron (PE) spectra, and band calculations based on local density approximation (LDA). Both the PE and $σ(ω)$ spectra not only in the high-temperature (HT) phase but also in the low-temperature (LT) phase as well as the energy gap formation owing to the MIT were almost consistent with those derived from the LDA band calculations, so the fundamental electronic structure in the HT and LT phases can be explained without electron correlations. However, the electronic structure in the middle phase between the HT and LT phases has not been clarified. The polarized $σ(ω)$ spectra revealed not only the anisotropic energy gap formation but also the anisotropic gap-opening temperature, i.e., the energy gap along the $c$ axis in the HT phase starts to open near the higher transition temperature, but that along the $b$ axis opens below the lower transition temperature. The finding suggests that the two-step MIT originates from the anisotropic energy gap formation.
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