Coherent phonons (CP) generated by laser pulses on the femtosecond scale have been proposed as a means to achieve ultrafast, non-thermal switching in phase-change materials such as Ge2Sb2Te5(GST). Here we use ultrafast optical pump pulses to induce coherent acoustic phonons and stroboscopically measure the corresponding lattice distortions in GST using 100 ps x-ray pulses from the ESRF storage ring. A linear-chain model provides a good description of the observed changes in the diffraction signal, however, the magnitudes of the measured shifts are too large to be explained by thermal effects alone implying the presence of transient non-equilibrium electron heating in addition to temperature driven expansion. The information on the movement of atoms during the excitation process can lead to greater insight into the possibilities of using CP-induced phase-transitions in GST.
@article{arxiv.1409.6888,
title = {Picosecond strain dynamics in Ge$_{2}$Sb$_{2}$Te$_{5}$ monitored by time-resolved x-ray diffraction},
author = {Paul Fons and Peter Rodenbach and Kirill V. Mitrofanov and Alexander V. Kolobov and Junji Tominaga and Roman Shayduk and Alessandro Giussani and Raffaella Calarco and Michael Hanke and Henning Riechert and Robert E. Simpson and Muneaki Hase},
journal= {arXiv preprint arXiv:1409.6888},
year = {2014}
}