以第一原理計算研究砷化鐵鋰與磷化鐵鋰摻雜鈷/鎳的晶格振動與超導性質

Abstract

自從鐵基超導體的超導性質被發現後，鐵基超導體就成為凝態物理裡熱門的研究主題。許多研究文獻顯示超導體在經過摻雜後，其超導轉移溫度會有所變化。這說明了在超導中摻雜扮演著非常重要的角色。 此論文中，我們利用密度泛函理論和密度泛函微擾理論來計算LiFeAs、LiFeP、Li(Co⁄Ni)xFe1-x As、Li(Co⁄Ni)xFe1-xP(x=0.02-0.12)的電子結構、聲子特性以及超導性質，並且討論摻雜對於LiFeAs和LiFeP的電子結構與聲子特性的影響。結果顯示，當摻雜濃度上升時，費米能級附近的態密度下降。而在聲子計算中，在聲子能譜裡隨著不同的摻雜濃度，在高頻的部分會有些微變動。經過計算後，全部材料的超導轉移溫度都非常低，與實驗並不相符。這說明這些材料的超導性質有可能不是以電子-聲子機制所誘發的。

Since the superconductivity was observed in the iron-based superconductors which becomes a popular topic in condensed matter physics. Many researches show that the superconducting transition temperature of the superconductors after doping changes. This implies that the doping effect plays an important role in the superconductivity. In this thesis, we use the Density Functional Theory and Density Functional Perturbation Theory to calculate the electronic structure, phonon properties and superconductivity of LiFeAs, LiFeP, Li(Co⁄Ni)xFe1-xAs and Li(Co⁄Ni)xFe1-xP with x=0.02-0.12 and discuss how the electron doping impacts on the electronic structure and phonon properties of LiFeAs and LiFeP. The results show that the density of states near the Fermi level decreases when the doping concentration increases. In phonon calculations, the resulting phonon dispersions show that they change at high frequency with different doping concentrations. The result superconducting transition temperatures of all materials are too low compared with the available experimental values. This means that the superconductivity in the iron-based superconductors may not be induced by the electron-phonon mechanism.