First-principles study of phonon properties in magnetic double-layer manganites
First-principles study of phonon properties in magnetic double-layer manganites
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磁性双层锰氧化物中声子特性的第一性原理研究
DOI：
10.1103/physrevb.86.014301
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发表时间：
2012
影响因子：
3.7
通讯作者：
K. Bohnen
中科院分区：
文献类型：
--
作者：
O. D. L. Pena;R. Heid;K. Bohnen
在密度泛函微扰理论框架下，采用混合基赝势方法和虚晶近似对La${}_{2\ensuremath{-}2x}$Sr${}_{1+2x}$Mn${}_{2}$O${}_{7}$(x=0.4)四方双层锰酸盐体系的晶格动力学性质进行了研究。通过对平面{q}{z}=0中铁磁性(FM)和非磁性(NM)基态的声子色散计算表明，磁序对涉及氧振动的高频模具有很强的影响，这些高频模涉及到Mn-O键伸展调制。它们可以追溯到像Mn-Mn或O-O这样的中程键的动力学耦合的变化，而最近邻的Mn-O键几乎保持不变。在电子学上，它们来源于NM相中主要的Mn$d({t}{2g})$轨道极化被FM相中的$d({e}{g})$型极化所取代。对[110]方向声子频率和声子强度的理论预测与之前在FM相中进行的中子散射实验符合得很好。最后，对电子-声子相互作用的计算表明，高频伸缩支链的色散与增强的电子-声子耦合有关，但平均而言，只获得了中等耦合常数。
We have studied the lattice dynamical properties of the tetragonal double-layer manganite system La${}_{2\ensuremath{-}2x}$Sr${}_{1+2x}$Mn${}_{2}$O${}_{7}$ ($x=0.4$) within the framework of density functional perturbation theory, using a mixed-basis pseudopotential method and the virtual-crystal approximation for modeling the alloy. Performing phonon dispersion calculations for both ferromagnetic (FM) and nonmagnetic (NM) ground states in the plane ${q}_{z}=0$ revealed a strong influence of the magnetic order on high-frequency modes which involve oxygen vibrations with Mn-O bond-stretching modulations. They can be traced back to changes in the dynamical coupling of medium-ranged bonds like Mn-Mn or O-O, while the nearest-neighbor Mn-O bonds remain practically unchanged. Electronically they originate from a replacement of the predominant Mn $d({t}_{2g})$ orbital polarization in the NM phase by a $d({e}_{g})$-type polarization in the FM phase. Good agreement is found between theoretical predictions for phonon frequencies and intensities in the [110] direction and a previous neutron scattering experiment performed in the FM phase. Finally, calculations of the electron-phonon interaction revealed that dips in the dispersion of the high-frequency bond-stretching branches are connected to an enhanced electron-phonon coupling, but on average only a moderate coupling constant of $\ensuremath{\lambda}=0.65$ is obtained.