Yimei Zhu

Department of Condensed Mater Physics and Materials Science
Brookhaven National Laboratory, Upton, NY 11973 USA

Interfaces with subtle difference in atomic and electronic structures in perovskite ABO₃ heterostructures often yield intriguingly different properties, yet their exact roles remain elusive. In this presentation, we report an integrated study of unusual transport, magnetic, and structural properties of Pr_0.67Sr_0.33MnO₃ films and La_0.67Sr_0.33MnO₃ films of various thicknesses on SrTiO₃ (STO) substrate. In particular, using atomically resolved imaging and electron energy-loss spectroscopy, we measure interface related local lattice distortion, BO₆ octahedral rotation and cation-anion displacement induced polarization. In the very thin Pr_0.67Sr_0.33MnO₃ film, an unexpected interface-induced ferromagnetic polaronic insulator phase was observed during the cubic-to-tetragonal phase transition of STO, due to the enhanced electron-phonon interaction and atomic disorder in the film. For the very thin La_0.67Sr_0.33MnO₃ films we reveal a remarkably deep polarization in non-ferroelectric STO near the interface due to its build-in electric field. Combining the experimental results including electron holography with first principles calculations, we propose that the observed deep polarization and field are originated from oxygen vacancies that extend beyond a dozen unit-cells from the interface, thus providing important evidence of the role of defects in the emergent interface properties of transition metal oxides.

The work was supported by DOE-BES-MSE under Contract DE-AC02-98CH10886. Collaborations with L. Wu, B. Zhang, G. M. Chow, Z. Wang, J. Tao, L. Yu, M-G. Han, J. Zhang, and E. W. Plummer are acknowledged.