Charge Density imaging of a ferroelectric-insulator interface with sub-Å resolution*

In complex oxide heterostructures, charge redistribution determines the characteristics of the material and can have significant influence on the behavior of the material. For example, the 2-dimensional electron gas at an LaAlO₃-SrTiO₃ interface is linked with superconductivity and ferromagnetism at the interface [1]. Although first principles calculations can provide highly detailed charge density maps that illustrate these phenomena, experimental methods often cannot resolve the same features at interfaces or nanostructures with high spatial resolution. Here we demonstrate the imaging of electron charge at interfaces in heterogeneous perovskite structures at atomic resolution using aberration corrected scanning transmission electron microscopy. The charge density mapping is determined using the 2D diffraction pattern acquired with a high-speed pixelated detector [2]. At a BiFeO₃-SrTiO₃ interface, we found evidence of charge separation caused by the penetration of the electric field from the polarized BiFeO₃ into the insulating SrTiO₃.

[1] J. A. Bert, et al., Nature Physics 7, 767 (2011)
[2] K. Müller, et al., Nature Communications 5, 5653 (2014)