Pressure dependence of phonon modes across the tetragonal to collapsed-tetragonal phase transition in CaFe 2 As 2
Pressure dependence of phonon modes across the tetragonal to collapsed-tetragonal phase transition in CaFe 2 As 2
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DOI：
10.1103/physrevb.81.144502
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发表时间：
2009-11
影响因子：
3.7
通讯作者：
R. Mittal;R. Heid;A. Bosak;T. Forrest;S. Chaplot;D. Lamago;D. Reznik;K. Bohnen;Y. Su;N. Kumar;S. Dhar;A. Thamizhavel;Christian Ruegg;M. Krisch;D. McMorrow;T. Brueckel;L. Pintschovius
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文献类型：
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作者：
R. Mittal;R. Heid;A. Bosak;T. Forrest;S. Chaplot;D. Lamago;D. Reznik;K. Bohnen;Y. Su;N. Kumar;S. Dhar;A. Thamizhavel;Christian Ruegg;M. Krisch;D. McMorrow;T. Brueckel;L. Pintschovius
用非弹性X射线和中子散射研究了CaFe_{2} As_{2}中大量声子模的压力依赖性，这些声子模的能量覆盖声子谱的整个范围.的压力范围是足够大的，以涵盖一级相变到所谓的崩溃阶段，其中$c$轴收缩约6%，而$a$和$B$轴膨胀约1.5%。我们的主要结果是，压力引起的声子频率的变化很好地解释了相关的键长在整个压力范围内，包括与一阶相变。具体而言，极化的声子在$ab$平面的频率，以及Fe-As键长变化不大的相变。另一方面，键沿着c$轴的大收缩对沿沿着c$方向传播的横向声学声子的响应非常显著.非磁性密度泛函计算描述的频率在零压力和崩溃阶段在一个令人满意的方式，如果基于各自的实验晶体结构。这表明，没有必要援引铁原子磁矩的变化来解释压力引起的频率偏移。
The pressure dependence of a large number of phonon modes in ${\text{CaFe}}_{2}{\text{As}}_{2}$ with energies covering the full range of the phonon spectrum has been studied using inelastic x-ray and neutron scatterings. The pressure range was large enough to cover the first-order phase transition into the so-called collapsed phase where the $c$-axis contracts by about 6% whereas $a$ and $b$ axes expand by about 1.5%. Our main result is that pressure-induced phonon frequency shifts are well explained by the changes in relevant bond lengths throughout the pressure range, including those associated with the first-order phase transition. Specifically, the frequencies of phonons polarized in the $ab$ plane as well as the Fe-As bond lengths change little across the phase transition. On the other hand, the transverse-acoustic phonons propagating along the $c$ direction stiffen very significantly in response to the large contraction of the bonds along the $c$ axis. Nonmagnetic density-functional calculations describe the frequencies in both the zero pressure and in the collapsed phase in a satisfactory way if based on the respective experimental crystal structures. This suggests that there is no need to invoke changes in magnetic moments on Fe atoms to explain the pressure-induced frequency shifts.