MgCNi_3的电子结构、光学性质与超导电性

A study on the electronic structure,superconductivity,and optical properties of MgCNi_3

用第一性原理的密度泛函能带计算方法研究了新近发现的超导体MgCNi3的电子能带结构 .计算结果表明其电子结构的基本特征是 :Ni的 3d态和C的 2p态的杂化组成了MgCNi3的导带 ,费米面附近的物理性质主要由来源于Ni的 3d电子态决定 .在费米能级 (EF)以下 3 0eV的范围内 ,Ni 3d态构成了能带色散微弱的密集电子态 ,EF 恰好落在Ni 3dyz +zx和 3d3z2 -r2 电子态密度 .C 2p态分布在EF 以下 4 0— 7 0eV的区域内 ,Mg主要是以二价离子Mg2 +的形式存在 .Mg原子的掺杂导致了Ni原子的 3d态基本上全部占据 ,引起Ni原子磁矩的消失 .费米能级EF 处的态密度N(EF)是 5 5 0 (states eV·cell) ,由此得到的Sommerfeld常数γeal～ 4 4 5mJ mol·K2 .基于第一性原理的光学性质的计算结果表明 :在 0— 12eV的范围内光吸收主要是从占据的Ni 3d态向C 2p和Ni4s的跃迁 .根据这些结果得出结论 :MgCNi3的超导电性基本上是强耦合的BCS电子 声子作用机理 .

In this article the density functional theory and LDA are used to study the electronic and optical properties of newly discovered alloy superconductor MgCNi3 The calculated results exhibit that the conduction bands in this compound are derived by Ni 3d and C 2p states. The top valence states have essentially Ni 3d characters and the C 2p states occupy the region from 4.0eV to 7. 0eV below Fermi energy. E-F locates just at the step slope of sharply structured Ni 3d(yz + zx) and 3d(3z2 - r2) peaks near E-F. The doping carriers from Mg atoms destroy the magnetic order. The calculated optical properties show that the optical conductivity in the energy range 0-12eV are contributed from the Ni 3d to Ni 4s and C 2p transitions. The density of states near Fermi energy N ( E-F) is evaluated to be 5.50 ( states/eV . cell) which yielded a Sommerfeld constant gamma(cal) similar to 4.45 mJ/mol . K-2. We conclude that the mechanism of superconductivity in MgCNi3 has the type of BCS with strong electron-phonon coupling.