LaFeAsO单晶各向异性光学性质的第一性原理研究

Ab-initio Investigation of Anisotropic Optical Properties of LaFeAsO

使用密度泛函第一性原理研究了高温超导体LaFeAsO各向异性的光学性质。在描述光学性质的计算原理和计算方法的基础上,计算了LaFeAsO的态密度、光电导谱、反射谱以及电子能量损失谱。光电导谱中,x方向与z方向有着很大差别,在沿x方向的第一个带间吸收峰出现在1.3eV处,沿z方向出现在1.5eV处;在反射谱与电子能量损失谱中,x方向与z方向的特征峰位置在能量较高处都是相互吻合的。分析认为,主要是电子在Fe原子之间的各个态间的跃迁所引起。考虑到温度效应对其光学性质的影响,在计算光学矩阵元时,加入Lorentz展宽δ=0.10eV。本文的研究结果,可为实验制备以及材料性质的研究提供有价值的参考。

The anisotropic optical properties for superconductor LaFeAsO have been stud- ied by full-potentiallinearized augmented plane wave （FLAPW） method based on density functional theory. In order to simulate the temperature effects, Lorentzian broadening （set as δ = 0. 10 eV） is added into optical matrix elements during the calculation in these spec- tra. The optical conductivity spectra σ（ω）, the reflectivity spectra R（ω） and electron ener- gy loss spectra have been calculated. LaFeAsO is an anisotropic single crystal. The optical conductivity spectra along x-axis display quite different features in comparison with those of z-axis entirely, and the reflectivity spectra coincide well with the corresponding electron energy loss spectra especially about the characteristic peaks. In the optic conductivity spectra, the first intraband absorption along x-axis appear at 1.3 eV while it is at 1.5 eV a- long z-axis. By further analysis, the properties are mainly caused by electronic transitions between the various states of the Fe atom.