title: Capturing ultrafast photoinduced local structural distortions of BiFeO3.
abstract: The interaction of light with materials is an intensively studied research forefront, in which the coupling of radiation energy to selective degrees of freedom offers contact-free tuning of functionalities on ultrafast time scales. Capturing the fundamental processes and understanding the mechanism of photoinduced structural rearrangement are essential to applications such as photo-active actuators and efficient photovoltaic devices. Using ultrafast x-ray absorption spectroscopy aided by density functional theory calculations, we reveal the local structural arrangement around the transition metal atom in a unit cell of the photoferroelectric archetype BiFeO3 film. The out-of-plane elongation of the unit cell is accompanied by the in-plane shrinkage with minimal change of interaxial lattice angles upon photoexcitation. This anisotropic elastic deformation of the unit cell is driven by localized electric field as a result of photoinduced charge separation, in contrast to a global lattice constant increase and lattice angle variations as a result of heating. The finding of a photoinduced elastic unit cell deformation elucidates a microscopic picture of photocarrier-mediated non-equilibrium processes in polar materials.
authors.affiliation: X-ray Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA.
authors.forename: Haidan
authors.initials: H
authors.lastname: Wen
authors.affiliation: Physical Sciences Division, Pacific Northwest National Laboratory, Richland, WA 99354, USA.
authors.forename: Michel
authors.initials: M
authors.lastname: Sassi
authors.affiliation: National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, 230029, China.
authors.forename: Zhenlin
authors.initials: Z
authors.lastname: Luo
authors.affiliation: Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853, USA.
authors.forename: Carolina
authors.initials: C
authors.lastname: Adamo
authors.affiliation: Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853, USA.|Kavli Institute at Cornell for Nanoscale Science, Ithaca, New York 14853, USA.
authors.forename: Darrell G
authors.initials: DG
authors.lastname: Schlom
authors.affiliation: Physical Sciences Division, Pacific Northwest National Laboratory, Richland, WA 99354, USA.
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Rosso
authors.affiliation: X-ray Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA.
authors.forename: Xiaoyi
authors.initials: X
authors.lastname: Zhang