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The coupling of light to nanoscale ferroelectric materials enables novel means of controlling their coupled degrees of freedom and engineering new functionality. Here we present femtosecond time-resolution nonlinear-optical measurements of light-induced dynamics within single ferroelectric barium titanate nanowires. By analyzing the time-dependent and polarization-dependent second harmonic intensity generated by the nanowire, we identify its crystallographic orientation and then make use of this information in order to probe its dynamic structural response and change in symmetry. Here, we show that photo-excitation leads to ultrafast, non-uniform modulations in the second order nonlinear susceptibility tensor, indicative of changes in the local symmetry ofmore » the nanostructure occurring on sub-picosecond time-scales.« less

Femtosecond resolution electron scattering techniques are applied to resolve the first atomic-scale steps following absorption of a photon in the prototypical hybrid perovskite methylammonium lead iodide. Following above-gap photoexcitation, we directly resolve the transfer of energy from hot carriers to the lattice by recording changes in the mean square atomic displacements on 10-ps time scales. Measurements of the time-dependent pair distribution function show an unexpected broadening of the iodine-iodine correlation function while preserving the Pb-I distance. This indicates the formation of a rotationally disordered halide octahedral structure developing on picosecond time scales. Here, this work shows the important role ofmore » light-induced structural deformations within the inorganic sublattice in elucidating the unique optoelectronic functionality exhibited by hybrid perovskites and provides new understanding of hot carrier-lattice interactions, which fundamentally determine solar cell efficiencies.« less