Ultrafast Suppression of the Ferroelectric Instability in KTaO_{3}
| Autor: | Viktor Krapivin, Mingqiang Gu, D. Hickox-Young, S. W. Teitelbaum, Y. Huang, G. de la Peña, D. Zhu, N. Sirica, M.-C. Lee, R. P. Prasankumar, A. A. Maznev, K. A. Nelson, M. Chollet, James M. Rondinelli, D. A. Reis, M. Trigo |
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| Rok vydání: | 2022 |
| Předmět: | |
| Zdroj: | Physical review letters. 129(12) |
| ISSN: | 1079-7114 |
| Popis: | We use an x-ray free-electron laser to study the ultrafast lattice dynamics following above band-gap photoexcitation of the incipient ferroelectric potassium-tantalate, \kto. % We use ultrafast near-UV (central wavelength 266\,nm and 50 fs pulse duration) laser light to photoexcite charge carriers across the gap and probe the ultrafast lattice dynamics by recording the x-ray diffuse intensity throughout multiple Brillouin zones using pulses from the Linac Coherent Light Source (LCLS) (central wavelength 1.3\,\AA\, and $< 10$~fs pulse duration). We observe changes in the diffuse intensity that we conclude are associated with a hardening of the soft transverse optical and transverse acoustic phonon branches along $\Gamma$ to $X$ and $\Gamma$ to $M$. Using ground- and excited-state interatomic force constants from density functional theory (DFT) and assuming the phonon populations can be described by a time-dependent temperature, we fit the quasi-equilibrium thermal diffuse intensity to the experimental time-dependent intensity. We obtain the instantaneous lattice temperature and density of photoexcited charge carriers as a function of time delay. The DFT calculations demonstrate that photoexcitation transfers charge from oxygen $2p$ derived $\pi$-bonding orbitals to Ta $5d$ derived antibonding orbitals, further suppressing the ferroelectric instability and increasing the stability of the cubic, paraelectric structure. Comment: 8 pages, 4 figures |
| Databáze: | OpenAIRE |
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