Emergent Phenomena at Oxide Interfaces Unveiled by Atom-by-Atom Spectroscopy
Ming-Wen Chu1*
1Center for Condensed Matter Sciences, National Taiwan University, Taipei, Taiwan
* presenting author:Ming-Wen Chu, email:chumingwen@ntu.edu.tw
With the assistance of modern thin-film growth techniques, perovskite oxides with a three-dimensional (3D) crystal structure can now be grown in a layer-by-layer manner at atomic-level precision, opening up vast opportunities for unprecedented phenomena at the heterostructural interface. The emergence of a conductive interface between the two insulating oxides, LaAlO3 (LAO) and SrTiO3 (STO) [A. Ohtomo and H. Y. Hwang, Nature 427, 423 (2004)], represents the most celebrated exemplification in this framework. Up to the date, otherwise oxide interfaces with a metallic character were found, whereas it is also noted that some oxide interfaces remain insulating despite the same heterostructure-design conception being exploited. To disentangle the puzzle, an atom-by-atom spectroscopic characterization across the interfaces is indispensable and the quantitative chemical and electronic mapping by electron energy-loss spectroscopy (EELS) represents the most powerful technique to this end. In this talk, I will explain the principles of atomically-resolved EELS and the unveiling of several distinct oxide-interfacial phenomena, including the unexpected existence of a localized two-dimensional (2D) electron density at the insulating (Nd,Sr)MnO3/STO interface, the condensation of 2D charges at the (Nd,Sr)MnO3/STO interface into one-dimensional electron chains, and the undocumented structural origin for the interfacial metallicity at the LAO/STO interface.

Keywords: oxide interface, electron energy-loss spectroscopy