Ultrafast dynamics in condensed matter: Cases for x-ray free electron lasers

Several examples of how (resonant) X-ray diffraction with ultrashort x-ray pulses can be used to study ultrafast electron – and structural dynamics in real time. Results on how we can optically trigger an electronic phase transition in a correlated electron system (manganites) and how the electronic and crystal structural react to it in real time are presented. [1,2] This will be compared to the case of exciting a particular phonon mode. [3] In the second part we look into the case of a pure structural phase transitions (in SrTiO3 [4] and EuTiO3) and how we can trigger it with an optical excitation. Will the atoms move when the lattice get warm or can we drive the transition faster? This will be compared to the case of exciting the polar soft mode of SrTiO3 where a strong driving field allows to upconvert phonons (excite phonon with higher energies). [5] Finally I will give a first glance on a successful experiment at the brand new SwissFEL facility at PSI that addresses the question: How fast can we localize an electron in a solid?

[1] P. Beaud et al., Nature Mater. 13, 923 (2014).
[2] V. Esposito et al., Phys. Rev. B 97, 014312 (2018).
[3] V. Esposito et al. Phys. Rev. Lett. 118, 247601 (2017)
[4] M. Porer et al., Phys. Rev. Lett. 121, 055701 (2018).
[5] M. Kozina et al., arXiv:1807.10788