Department of Physics, University College Cork, Cork T12K8AF, Ireland.
Tyndall National Institute, Cork T12R5CP, Ireland.
Phys Rev Lett. 2019 Aug 23;123(8):087401. doi: 10.1103/PhysRevLett.123.087401.
We present a first-principles method for the calculation of the temperature-dependent relaxation of symmetry-breaking atomic driving forces in photoexcited systems. We calculate the phonon-assisted decay of the photoexcited force on the low-symmetry E_{g} mode following absorption of an ultrafast pulse in Bi, Sb, and As. The force decay lifetimes for Bi and Sb are of the order of 10 fs and in agreement with recent experiments, demonstrating that electron-phonon scattering is the primary mechanism relaxing the symmetry-breaking forces. Calculations for a range of absorbed photon energies suggest that larger amplitude, symmetry-breaking atomic motion may be induced by choosing a pump photon energy which maximizes the product of the initial E_{g} force and its lifetime. The high-symmetry A_{1g} force undergoes a partial decay to a nonzero constant on similar timescales, which has not yet been measured in experiments. The average imaginary part of the electron self-energy over the photoexcited carrier distribution provides a crude indication of the decay rate of symmetry-breaking forces.
我们提出了一种计算光激发体系中打破对称性原子驱动力随温度弛豫的第一性原理方法。我们计算了 Bi、Sb 和 As 中吸收超快脉冲后，低对称 E_{g}模式下光激发力在声子辅助下的衰减。Bi 和 Sb 的力衰减寿命约为 10fs，与最近的实验结果一致，表明电子-声子散射是弛豫对称破缺力的主要机制。对于一系列吸收光子能量的计算表明，通过选择最大程度地提高初始 E_{g}力与其寿命的乘积的泵浦光子能量，可以诱导更大振幅、对称性破缺的原子运动。在相似的时间尺度上，高对称性 A_{1g}力经历部分衰减到非零常数，这在实验中尚未测量到。光激发载流子分布上的电子自能的平均虚部提供了对称破缺力衰减率的粗略指示。
