Abstract
We use an x-ray free-electron laser to study the lattice dynamics following photoexcitation with ultrafast near-UV light (wavelength 266 nm, 50 fs pulse duration) of the incipient ferroelectric potassium tantalate, . By probing the lattice dynamics corresponding to multiple Brillouin zones through the x-ray diffuse scattering with pulses from the Linac Coherent Light Source (LCLS) (wavelength 1.3 Å and pulse duration), we observe changes in the diffuse intensity associated with a hardening of the transverse acoustic phonon branches along to and to . Using force constants from density functional theory, we fit the quasiequilibrium intensity and obtain the instantaneous lattice temperature and density of photoexcited charge carriers. The density functional theory calculations demonstrate that photoexcitation transfers charge from oxygen derived -bonding orbitals to Ta derived antibonding orbitals, further suppressing the ferroelectric instability and increasing the stability of the cubic, paraelectric structure.
- Received 29 January 2022
- Revised 23 May 2022
- Accepted 19 July 2022
DOI:https://doi.org/10.1103/PhysRevLett.129.127601
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