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Atomic-scale control of ferroelectricity and transport in ultrathin transition-metal-oxide heterostructures

Speaker: Dr. WANG Lingfei
Seoul National University
Time: 2017-10-10 15:00
Place: ROOM 9004, Hefei National Laboratory Building


  During the last two decades, due to the rapid advancements in heteroepitaxial growth techniques, it has become feasible to reduce the oxide film thickness to nanometer scale while retaining the original ferroic order. These advances enable oxide-based electronic devices with superior functionalities. In such ultrathin epitaxial systems, the interface/surface structure becomes crucial in determining and controlling the functionalities in atomic scale.
  In this presentation, we first demonstrated a selective control of interfacial termination sequence in SrRuO3/BaTiO3/SrRuO3 (SRO/BTO/SRO) heterostructures. Depending on the termination sequence at SRO/BTO interface, the ferroelectric stability of BTO ultrathin film changes significantly. Secondly, taking ultrathin BaTiO3 films as a model system, we found an intrinsic tunneling conductance enhancement near the terrace edges. Combining the advanced scanning probe microscopy and first-principles calculations, we demonstrate that the terrace edge geometry can trigger an intrinsic electronic reconstruction. The resultant free carriers reduce the effective tunneling barrier width locally and facilitate the tunneling conduction. At last, we investigated the magnetotransport properties of ultrathin SrRuO3 (SRO) films with BaTiO3 (BTO) ferroelectric capping layers. By reducing the SRO film thickness below 5 unit-cells, we observed not only the anomalous Hall effect but also a pronounced topological Hall effect. The topological Hall signal indicates that magnetic skyrmions could be stabilized in this oxide heterostructure. The scanning transmission electron microscopy results show that the ferroelectric atomic displacement in BTO layers can penetrate into SRO films by approximately 3 unit-cells. The associated inversion-symmetry-breaking can enhance the Dzyaloshinski-Moriya interaction and consequently trigger the magnetic skyrmion states.

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