元素替代对LaO_0.5F_0.5Bi(Se_1-xS_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_0.5F_0.5Bi(Se_1-xS_x)₂ Superconductor

DOI: 10.12677/CMP.2015.43011, PP. 93-101

Keywords: LaO_0.5F_0.5Bi(Se_1-xS_x)₂，元素替代，晶格参数，电子结构
LaO_0.5F_0.5Bi(Se_1-xS_x)₂, Element Substitution, Lattice Parameter, Electronic Structure

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Abstract:

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LaO_0.5F_0.5Bi (Se_1？xS_x)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LaO_0.5F_0.5BiSe₂和LaO_0.5F_0.5BiS₂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LaO_0.5F_0.5Bi (Se_0.5S_0.5)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LaO_0.5F_0.5Bi (Se_1？xS_x)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 LaO_0.5F_0.5Bi(Se_1？xS_x)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 LaO_0.5F_0.5BiSe₂ and LaO_0.5F_0.5BiS₂, 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 LaO_0.5F_0.5Bi(Se_0.5S_0.5)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 LaO_0.5F_0.5Bi(Se_1？xS_x)₂ may be an electron-phonon coupling superconductor.

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