Kavli Affiliate: Darrell G. Schlom
| First 5 Authors: Jakob Gollwitzer, Jeffrey Z. Kaaret, Y. Eren Suyolcu, Guru Khalsa, Rylan C. Fernandes
| Summary:
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.
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