铁基氟化物超导体SrFe_(1-x)Co_xAsF(x=0,0.125)声子特性的第一性原理计算研究

采用基于第一性原理的平面波赝势方法,计算了铁基氟化物及其钴掺杂超导体SrFe1-xCoxAsF(x=0,0.125)在四方非磁态与正交条纹反铁磁态下的声子谱(声子色散曲线、声子态密度)及电-声子耦合常数.计算发现:条纹反铁磁相互作用下的自旋-声子耦合效应强于电-声子耦合作用使声子谱的宽度减小;自旋效应使声子的有效质量增加导致条纹反铁磁态下Fe原子与As原子的耦合振动频率减小.另外,掺杂和自旋效应是提高电-声子耦合常数的两个有效方法,但计算所得超导转变温度远小于实验测量值,表明铁基超导电性非简单的电-声子耦合配对机理.

First-principles study on phonon properties of iron-based fluoride superconductors SrFe1-xCoxAsF (x=0, 0.125)

Using plane-wave pseudopotential method based on first-principles, we calculate the phonon spectra (including phonon dispersion curves and phonon density of states) and electron-phonon coupling constants of SrFe_1-xCo_xAsF (x=0, 0.125) in tetragonal nonmagnetic (NM) and orthorhombic striped antiferromagnetic (SAF) states. Results show that under striped antiferromagetic interaction the spin-phonon coupling is stronger than the electron-phonon coupling, leading to the decrease of phonon spectra width; and the increased effective phonon quality due to spin effects makes the frequencies of coupling vibration between Fe and As atoms reduced. In addition, doping and spin effects are two effective methods to enhance the electron-phonon coupling, however, the calculated superconducting transition temperature is far lower than the experimental measurement, which rules out the simple electron-coupling superconducting pairing mechanism in SrFe_1-xCo_xAsF.
Keywords：iron-based fluoridephonon propertyelectron-phonon couplingsuperconductivity