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arXiv · 1903.00744

Ultrafast relaxation of symmetry-breaking photo-induced atomic forces

Shane M. O'Mahony·Felipe Murphy-Armando·Éamonn D. Murray·José D. Querales-Flores·Ivana Savić·Stephen Fahy
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Abstract

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 the prototypical group-V semimetals, Bi, Sb and As. The force decay lifetimes for Bi and Sb are of the order of $10$ fs and in good agreement with recent experiments, demonstrating that electron-phonon scattering is the dominant 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 maximises the product of the initial $E_g$ force and its lifetime. We also find that the high-symmetry $A_{1g}$ force undergoes a partial decay to a non-zero constant on similar timescales, which has not yet been measured in experiments. We observe that the imaginary part of the electron self-energy, averaged over the photoexcited carrier distribution, provides a reasonable estimate for the decay rate of symmetry-breaking forces.

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Shane M. O'Mahony, Felipe Murphy-Armando, Éamonn D. Murray, José D. Querales-Flores, Ivana Savić, Stephen Fahy. 2019-03-02. Ultrafast relaxation of symmetry-breaking photo-induced atomic forces. https://doi.org/10.1103/physrevlett.123.087401

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