We investigate the ultrafast structural dynamics of LaAlO3 thin films driven by short mid-infrared laser pulses at 20 THz. Time-resolved X-ray diffraction reveals an immediate lattice expansion and an acoustic breathing mode of the film. First-principles theory and a spring-mass model identify the direct coupling between coherently driven infrared-active phonons and strain as the underlying mechanism. Time-resolved optical birefringence measurements confirm that the amplitude of this acoustic mode scales linearly with the pump fluence, which agrees with the theory. Furthermore, time-resolved X-ray diffuse scattering indicates that THz excitation enhances crystallinity by inducing a non-thermal increase in structural symmetry originating from preexisting defects. These findings highlight the potential of a multimodal approach-combining time-resolved X-ray and optical measurements and first-principles theory-to elucidate and control structural dynamics in nanoscale materials.
@article{arxiv.2412.17192,
title = {Picosecond expansion in LaAlO3 resonantly driven by infrared-active phonons},
author = {Jakob Gollwitzer and Jeffrey Z. Kaaret and Y. Eren Suyolcu and Guru Khalsa and Rylan C. Fernandes and Oleg Gorobtsov and Sören Buchenau and ChanJu You and Jayanti Higgins and Ryan S. Russell and Ziming Shao and Yorick A. Birkhölzer and Takahiro Sato and Matthieu Chollet and Giacomo Coslovich and Mario Brützam and Christo Guguschev and John W. Harter and Ankit S. Disa and Darrell G. Schlom and Nicole A. Benedek and Andrej Singer},
journal= {arXiv preprint arXiv:2412.17192},
year = {2024}
}