Ultrafast Relaxation Dynamics of the Antiferrodistortive Phase in Ca Doped SrTiO3

作者：Porer M^*; Fechner M; Bothschafter E M; Rettig L; Savoini M; Esposito V; Rittmann J; Kubli M; Neugebauer M J; Abreu E; Kubacka T; Huber T; Lantz G; Parchenko S; Grubel S; Paarmann A; Noack J; Beaud P; Ingold G; Aschauer U; Johnson S L; Staub U^*

来源：Physical Review Letters, 2018, 121(5): 055701.

DOI：10.1103/PhysRevLett.121.055701

The ultrafast dynamics of the octahedral rotation in Ca:SrTiO3 is studied by time-resolved x-ray diffraction after photoexcitation 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 an ultrafast relaxation on a 0.2 ps timescale of the rotation of the oxygen octahedron, which is found to be independent of the initial temperature 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.

• 出版日期2018-8-3