Spatially Heterogenous Structural Dynamics of NdNiO3 Thin Films

<i>Rare earth nickelates display insulator-metal transition which is accompanied by a magnetic transition, charge ordering, and a crystal structure change. Laser-excitation drives the transition at ultrafast timescales providing an avenue to understand the role of coupled transitions in causing the transition. We utilized time-resolved x-ray diffraction to study the structural dynamics of epitaxial NNO thin film by observing the photoinduced changes in the (002) Bragg peak. The out of plane lattice parameter contracts for low fluences and expands for high fluences after laser excitation. A thermal model explains experimental trends revealing the potential for controlling structural dynamics via heteroepitaxial strain. Similar recovery timescales of structural and magnetism dynamics indicate a strong magneto-structural coupling is prevalent in the ultrafast recovery process. The change in integrated intensity and FWHM of the (002) peak indicate photoinduced domain dynamics which corroborates an ultrafast conductivity study proposing recovery via nucleating and growth in NNO. We present direct evidence of phase separation using time-resolved nanodiffraction. Spatiotemporally resolved characterization clearly shows the spatial heterogeneity of the structural dynamics in nickelates.</i>