掺杂MgCNi3超导电性和磁性的第一性原理研究

从第一性原理出发，计算了MgCNi₃的电子能带结构.MgCNi₃中C 2p与Ni 3d轨道杂化使穿梭费米面上的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.vHs峰上大的电子态密度和铁磁相变点附近的自旋涨落是决定MgCNi₃超导电性的重要因素.研究了三种替代式掺杂对其超导电性和磁性的影响，发现电子掺杂使费米能级下滑到态密度较低的位置，导致体系转变为无超导电性的顺磁相；同构等价电子数的金属间化合物的轨道杂化，引起费米面上态密度的减少，降低了超导电性；而空穴掺杂使费米面向vHs峰值方向移动，虽然费米面上电子态密度增大可能提高超导电性，但增强了的Ni原子磁交换作用产生铁磁序，破坏了超导电性.关键词：电子结构超导电性磁性掺杂

First-principles calculations on the superconductivity and magnetism of doping MgCNi3

We use the first-principles method to calculate the electronic band structures of MgCNi_3. The calculated results show that the hybridization between C 2p and Ni 3d electron orbits leads to the planar characteristic of Ni 3d band. The Fermi level is located on the right slope of the van Hove singularity (vHs) peak. The high density of states (DOS) at the Fermi level with vHs and large magnetic fluctuations near the ferromagnetic phase transition point are the important factors for the superconductivity of MgCNi_3. We study the variance of superconductivity and magnetism for three types of substitute doping in MgCNi_3,and find that the electron doping moves the Fermi level to the lower DOS side,and transforms MgCNi_3 to paramagneticm phase without superconductivity. The inter-metal compounds with the same valence electrons doping change the shape of Fermi surface,resulting from the hybridization between atoms. The decrease of the DOS decreases their superconductivity. The hole doping enhances the DOS at the Fermi level on the peak of vHs,but the large magnetic exchange interactions induce the ferromagnetic order,and the superconductivity disappears abruptly.