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The effects of above band gap ultrafast laser pulses on the lattice dynamics and structural properties of the prototypical perovskite, BaTiO3, are investigated using electronic structure methods and atomistic simulations. A constrained density functional method[1][2] is first used to study the local changes induced by ultrafast laser excitation. Our work shows a reduction in the ionicity due to electrons being returned by O anions to Ti cations. By phonon and equilibrium structure calculations, we find that moderate levels of photo-excitation reduces the polarization, coherently excites and softens optical A1 phonons, and lowers the local barriers to ferroelectric domain reversal, which further suggest a lowering of the coercive field and the phase transition temperature. The information gained from our first principles calculations is used to make suitable electronically-excited state atomistic potentials and to study significantly longer time-scales’ structural changes. We suggest that pump-probe spectroscopy could be used to induce a purely-displacive transition to higher symmetry phase at low temperature and to study the decay of coherent optical phonons. Our findings may also provide guidance to the design of optically controlled devices.
Supported by EPSRC grants EP/L015579/1, EP/P020194/1.[1] ´E. D. Murray et.al. Phys. Rev. B 72, 060301 (2005)
[2] P. Tangney and S. Fahy, Phys. Rev. B 65, 054302 (2002)
Fangyuan is a PhD student in the Doctoral Training Centre on Theory and Simulation of Materials at Imperial College London. She did her undergraduate study in the Department of Applied Physics at The Hong Kong Polytechnic University and then received a Master’s degree at Imperial College London. Her research focuses on how ultrafast optical excitation can be used to control structural changes in multiferroic materials such as phase transition and ferroelectric domain reversal. This work will help develop a fundamental physical understanding of perovskite multiferroics and open new possibilities in the design and optimisation of optically controlled devices.
Venue: TDLI Meeting Room 200
Here is video link:https://vshare.sjtu.edu.cn/open/ff66d8b8c891da7a67c7c9b17a3fd0d1