Li_2C_2中电声耦合及超导电性的第一性原理计算研究  

First-principles study of electron-phonon coupling and superconductivity in compound Li_2C_2

作　　者：高淼[1,2] 孔鑫[1] 卢仲毅[2] 向涛[1,3] 

机构地区：[1]中国科学院物理研究所,北京100190 [2]中国人民大学物理系,北京100872 [3]北京量子物质协同创新中心,北京100190

出　　处：《物理学报》2015年第21期1-8,共8页Acta Physica Sinica

基　　金：国家重点基础研究发展计划(批准号:2011CBA00112);国家自然科学基金(批准号:11190024;11404383);中国博士后科学基金资助项目(批准号:2014M561084)~~

摘　　要：通过第一性原理密度泛函和超导Eliashberg理论计算,我们研究了Li2C2在Cmcm相的电子结构和电声耦合特性,预言这种材料在常压和5GPa下是由电声耦合导致的转变温度分别为13.2 K和9.8 K的超导体,为实验上探索包含一维碳原子链的材料中是否可能存在超导电性、发现新的超导体提供了理论依据.如果理论所预言的Li2C2超导电性得到实验的证实,这将是锂碳化物中转变温度最高的超导体,高于实验观测到的LiC2的1.9 K和理论预言的单层LiC6的8.1 K超导转变温度.One-dimensional carbon chains are expected to show outstanding optical and mechanical properties. But synthesis of the compounds containing one-dimensional carbon chains is a challenging work, because of the difficulty in saturating the dangling bonds of carbon atoms. Recently, the transition from the Immm phase to the Cmcm one at a transition pressure 5 GPa has been predicted for Li2C2 by density-functional theory calculations. In Cmcm-Li2C2,there are one-dimensional zigzag carbon chains caged by lithium atoms. Under ambient pressure, the electronic structure of Cmcm-Li2C2 is as follows： The hybridization among 2s, 2py, and 2pzorbitals of carbon atoms results in three sp2-hybridized orbitals that are coplanar with the zigzag chains of these carbon atoms, denoted as the y-z plane. The sp2-hybridized orbitals along y-axis（perpendicular to the zigzag chain） overlap with each other and form one π-bonding band and one π＊-antibonding band. Likewise, the 2pxorbitals of carbon atoms will provide also one π-bonding band and one π＊-antibonding band. These two π＊-antibonding bands cross the Fermi level and contribute to the metallicity of Cmcm-Li2C2. The other two sp2-hybridized orbitals will give two σ-bonding bands, whose band tops are about 5e V below the Fermi energy level. These two fully occupied σ bands are the framework of the zigzag carbon chains.The changes in electronic structure of Cmcm-Li2C2 under 5 GPa are negligible, compared with that in case of ambient pressure. To our best knowledge, there is no report upon the superconductivity for compounds containing one dimensional carbon chains. We choose Cmcm-Li2C2 as a model system to investigate its electron-phonon coupling and phonon-mediated superconductivity. To determine the phonon-mediated superconductivity, the electron-phonon coupling constant λ and logarithmic average frequency ωlogare calculated based on density functional perturbation theory and Eliashberg equations. We find that λ and ωlogare equal to 0.63 and 53.8 me V respective

关 键 词：电声耦合 超导电性 第一性原理计算 

分 类 号：O511.3[一般工业技术—材料科学与工程]