Na $_2$ KSb和NaK $_2$ Sb的电子结构和光学性质的第一性原理多体理论研究
Electronic structure and optical properties of Na$_2$KSb and NaK$_2$Sb from first-principles many-body theory
摘要：
在寻找用于真空电子源的新材料中，多碱金属锑化物，特别是锑化钠钾，由于其良好的电子和光学性质，最近被认为是特别有前途的。在密度泛函理论和多体微扰理论的框架下，我们研究了该家族的两个代表性成员，即Na $_2$ KSb和NaK $_2$ Sb的电子结构和介电响应。我们发现这两种材料都具有直接带隙，Na $_2$ KSb和NaK $_2$ Sb的直接带隙分别为1.5 eV和1.0 eV。价带和导带分别由具有p-和s-特征的Sb状态支配。的介电函数的虚部，计算明确包括电子-空穴相互作用的材料的光学响应的特征，表现出最大值从近红外区域开始，延伸到可见光和紫外波段。通过我们的分析，我们澄清了最低能量的激发是非激子的性质，它们的结合能是100毫电子伏的顺序。我们的研究结果证实了潜在的钠$_2$ KSb和钠K $_2$ Sb作为光电发射材料的真空电子源，光电倍增管，和成像设备。
英文摘要：
In the search for novel materials for vacuum electron sources, multi-alkali antimonides and in particular sodium-potassium-antimonides have been recently regarded as especially promising due to their favorable electronic and optical properties. In the framework of density-functional theory and many-body perturbation theory, we investigate the electronic structure and the dielectric response of two representative members of this family, namely Na$_2$KSb and NaK$_2$Sb. We find that both materials have a direct gap, which is on the order of 1.5 eV in Na$_2$KSb and 1.0 eV in NaK$_2$Sb. In either system, valence and conduction bands are dominated by Sb states with p- and s-character, respectively. The imaginary part of the dielectric function, computed upon explicit inclusion of electron-hole interactions to characterize the optical response of the materials, exhibits maxima starting from the near-infrared region, extending up to the visible and the ultraviolet band. With our analysis, we clarify that the lowest-energy excitations are non-excitonic in nature and that their binding energy is on the order of 100 meV. Our results confirm the potential of Na$_2$KSb and NaK$_2$Sb as photoemissive materials for vacuum electron sources, photomultipliers, and imaging devices.
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