2, University of Minnesota, Minneapolis, Minnesota, United States
Unusual transport or magnetic phenomena induced by octahedral distortions at the interfaces between substrates and thin films have been studied intensely for the last few years. In transition metal perovskite oxides, the rotation or tilt of the oxygen octahedra in the substrates can couple into the thin films, resulting in atomic or electronic structure configuration not seen in bulk materials. Ferromagnetic La0.5Sr0.5CoO3-δ thin films grown on SrTiO3 have been shown to favor periodic oxygen vacancy ordering as the result of interfacial strain from the substrate. Moreover, SrTiO3 undergoes an antiferrodistortive phase transition from cubic to tetragonal structure at 105 K, driven by the TiO6 octahedral rotation. This breaks the structural symmetry and induces orbital reconstructions in the interfacial Ti-O-Co bonds, which will distort both the CoO6 octahedral and CoO4 tetrahedral structure in the thin film. In this work, we use aberration-corrected scanning transmission electron microscopy (STEM) combined with in-situ cooling to investigate the atomic and electronic structure of La0.5Sr0.5CoO3-δ thin films grown on SrTiO3 with respect to the SrTiO3 transition at 105K. Atomic-resolution imaging and electron energy-loss spectroscopy (EELS) are used to examine changes in the local density of states and magnetic moments as a function of sample temperature.
Acknowledgement: This work is supported by a grant from NSD (DMR-1408427). Support from the UIC Research Resources Center (RRC), in particular A.W. Nicholls and F. Shi is acknowledged. Work at UMN is supported by the DOE.