M. Porer, M. Fechner, E. Bothschafter, L. Rettig, M. Savoini, V. Esposito, J. Rittmann, M. Kubli, M. J. Neugebauer, E. Abreu, T. Kubacka, T. Huber, G. Lantz, S. Parchenko, S. Grübel, A. Paarmann, J. Noack, P. Beaud, G. Ingold, U. Aschauer, S. L. Johnson, U. Staub:
Phys. Rev. Lett. 121(5), 055701 (2018), pp.5;
arXiv:1805.00580 [cond-mat.mtrl-sci] (2018), pp. 11;
DOI: arXiv:1805.00580 [cond-mat.mtrl-sci]
The ultrafast dynamics of the octahedral rotation in Ca:SrTiO3 is studied by time resolved x-ray diffraction after photo excitation over the band gap. By monitoring the diffraction intensity of a superlattice reflection that is directly related to the structural order parameter of the soft-mode driven antiferrodistortive phase in Ca:SrTiO3, we observe a ultrafast relaxation on a 0.2 ps timescale of the rotation of the oxygen octahedron, which is found to be independent of the initial temperaure despite large changes in the corresponding soft-mode frequency. A further, much smaller reduction on a slower picosecond timescale is attributed to thermal effects. Time-dependent density-functional-theory calculations show that the fast response can be ascribed to an ultrafast displacive modification of the soft-mode potential towards the normal state, induced by holes created in the oxygen 2p states.
The original publication is available by link DOI: 10.1103/PhysRevLett.121.055701