三元硅化物CaAlSi的结构和超导电性  

Structure and superconductivity of the ternary silicide CaAlSi

作　　者：马荣[1] 黄桂芹[2] 刘楣[1] 

机构地区：[1]东南大学物理系,南京210096 [2]南京师范大学物理系,南京210097

出　　处：《物理学报》2007年第8期4960-4964,共5页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:10574021);高等学校博士学科点专项科研基金(批准号:20060286044)资助的课题.~~

摘　　要：应用线性响应的线性糕模轨道方法计算AlB2型结构的新超导体CaAlSi的电子能带、声子谱及电子-声子耦合常数,并讨论了它们的超导电性.通过比较两种结构模型的计算结果可以看出:若CaAlSi中Al,Si原子沿c轴方向以—Al—Al—Al—(或—Si—Si—Si—)排列,低频B1g模式的声子频率沿A-L方向出现虚频,使得这种结构处于不稳定状态,电子-声子耦合表现异常增大;若Al,Si原子沿c轴方向以—Al—Si—Al—排列,声子振动模式的增加消除了低频声子的异常软化.由此计算得到的声子对数平均频率增大为147K,电子-声子耦合常数λ=0.80.用中等耦合强度的Bardeen-Cooper-Schrieffer理论可合理解释其超导电性.Using response-linearized linear muffin-tin orbital method we have studied the electronic band structure, phonon spectra, electron-phonon coupling and superconductivity of the new superconductor CaAISi with A1B2-type structure. The following conclusions are drawn from our calculations. （1） If A1 and Si atoms are assumed to be arranged along the c-axis in a long-range ordered （-A1-A1-A1- and -Si-Si-Si-） structure, one should obtain the uhrasoft B1g phonon mode and hence very strong electren-phonon coupling in CaAlSi. However, the appearance of imaginary frequency phonon modes indicates the instability of such a structure. （2） For A1 and Si atoms arranged along the c-axis in a long-range ordered （-A1-Si-A1-） structure, the calculated electren-phonon coupling constant is equal to λ=0.80 and logarithmically averaged frequency ωln is 147 K. This calculated result can correctly yield the superconduction transition temperature of CaAlSi by the standard Bardeen- Cooper-Schrieffer theory for moderate electren-phonon coupling strength.

关 键 词：超导电性 能带结构 声子频率 电子-声子耦合 

分 类 号：O511.2[理学—低温物理]