【作者】 杜锦丽；

【导师】 刘楣；

【作者基本信息】 东南大学 ， 凝聚态物理， 2006， 硕士

【摘要】 我们用全势线性缀加平面波方法计算研究了两类新超导体的超导电性。第一部分用双层超格子原胞模型计算三元硅化物CaAlSi的电子能带结构,用带心冻结声子法计算了声子频率及电-声子耦合常数,并讨论了它们的超导电性。考虑到Al,Si原子分布的无序性和完全等价性,以及低频B_1g1声子频率的非谐性效应,计算得到稳定的低频B_1g声子频率为1101cm^-1。对超导电性有较大贡献的Ca d态电子与B_1g振动模式间的电-声子耦合常数为0.37。我们的结果与用虚晶近似的结果是一致的。并证明CaAlSi的超导电性可由中等耦合强度的BCS理论来解释。第二部分工作用虚晶模型和考虑了局域自旋密度近似（LSDA）研究具有反钙钛矿结构的新超导体MgCNi₃的超导电性与磁性随掺杂度的变化。首先用WEIN2K程序包计算了MgCNi₃的电子能带结构和态密度。计算结果表明,MgCNi₃中C 2p与Ni 3d轨道杂化使穿越费米面上的Ni 3d能带表现出平面性,费米面落在态密度范霍夫奇异（vHs）峰的右坡上。位于铁磁相变点附近的MgCNi₃中Ni d电子具有大的自旋涨落,其态密度又接近峰值,因此这两个特点使材料处于不稳定的边缘而产生相变。而后对MgCNi₃中Mg位分别用Na （空穴）和Al （电子）掺杂,研究Mg_1-xNa_xCNi₃和Mg_1-xAl_xCNi₃ （ 0≤x≤0.5）系列化合物的超导电性和磁性变化。研究结果表明:对于空穴掺杂的Mg_1-xNa_xCNi₃,随着掺杂度x的增大,费米面向下方的vHs峰值移动。虽然总态密度增大,但大的自旋涨落使自旋极化向上和向下的态密度分裂开来,破坏了超导库柏对的配对,因而超导电性减弱。在掺杂为x=0.09处,自旋劈裂使Mg_1-xNa_xCNi₃产生磁矩,表现出磁性。对于电子型掺杂Mg_1-xNa_xCNi₃,随着x的增加,费米面向vHs右坡下移,使N（E_F ）不断减小,从更多还原

【Abstract】 We use FP-LAPW method to study the superconductivity of two type new superconductors. In the first part, considering the randomly distributed of Al and Si atoms not only over the in-plane but also along the c direction，we chose the simplest double cell model to calculate the electronic band structure. Using zone-center frozen phonon method, and considering the anharmonicity of phonon frequency , we calculate the phonon frequencies and electron-phonon coupling constant of B1g mode. we obtain the phonon frequency of B_1g mode to be 110cm^-1, and the electron-phonon coupling constant between Ca d electron and B_1g phonon mode is 0.37. The calculated results are consistent with that by using the model of virtual-crystal aproximation, and proved that the superconductivity in CaAlSi can be well explained by the standard BCS theory in the moderate electron-phonon coupling strength.In the second part, we study the superconductivity and magnetic properties of new superconductor MgCNiwith antiperovskite structure. First, we calculate the electronic band structure and denstity of states （DOS） of MgCNi, and the calculated results show that the hybridization between C 2p and Ni 3d electron orbits lead to the plan characteristic of Ni 3d band. The Fermi level is located in the vicinity of the van Hove singularity（vHs） peak, which made MgCNi₃ to be a strong coupling superconductivity. Then, considering the local spin density approximation （LSDA） and using the model of virtual-crystal approximation, we study the variance of superconductivity and magnetism of Mg_1-xNa_xCNi₃ and Mg_1-xAl_xCNi₃at doping 0≤x≤0.5. The calculated results show that both hole doping and electron doping quench superconductivity, but the reason are differences. The former is that the increased magnetic更多还原