元素替代对LaO_(0.5)F_(0.5)Bi(Se_(1-x)S_(x))_(2)超导体晶格和电子结构的影响

The Effects of Element Substitution on the Crystal Lattice and Electronic Structure of LaO_(0.5)F_(0.5)Bi(Se_(1−x)S_(x))_(2)Superconductor

基于第一性原理计算,本文研究了S元素替代对最近新发现的BiSe2基超导体LaO0.5F0.5Bi (Se1?xSx)2晶格和电子结构的影响。发现随着S掺杂浓度的增加,晶格参数a,c以及原胞体积V都呈下降的趋势。研究了LaO0.5F0.5BiSe2和LaO0.5F0.5BiS2的电子结构,发现二者都具有多带结构,费米面具有准二维结构,费米处的态密度主要来自于Bi-6p轨道。然后运用两种不同方法建立LaO0.5F0.5Bi (Se0.5S0.5)2原胞模型,发现两者费米面出现显著不同,表明Se1和Se2位置原子的不等价性。最后计算发现随着S掺杂浓度的增大,费米面处态密度先增大再减小,在x = 0.6时取得最大值,与实验描绘的Tc^x相图基本一致,预示着LaO0.5F0.5Bi (Se1-xSx)2可能为电声耦合的常规超导体。

Based on first-principle calculations, this work investigates the effects of element substitution on the crystal lattice and electronic structure of the newly discovered BiSe2-based superconductor LaO0.5F0.5Bi(Se1?xSx)2. With the increase of S doping level, it is found that the lattice parameters a, c, and the unit-cell volume V gradually decrease. For the electronic structure of LaO0.5F0.5BiSe2 and LaO0.5F0.5BiS2, they both have multi-band structure, and show quasi two-dimensional Fermi surface (FS). The density of states (DOS) at the FS mainly comes from Bi-6p orbital. For LaO0.5F0.5Bi(Se0.5S0.5)2, using two different models established by different unit-cell model, we find that their FSs are significantly different, indicating the inequivalence of Se1- and Se2-position atoms. Besides, with the increasing of S doing level, the DOS at Fermi energy firstly increases and then decreases. When the concentration of S is x = 0.6, the DOS has a maximum value, which is consistent with the experimental Tc^x phase diagram, indicating that LaO0.5F0.5Bi(Se1-xSx)2 may be an electron-phonon coupling superconductor.