Emergent Charge Condensations at Two-Dimensional Oxide Interfaces
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 crystal structure can now be grown in a layer-by-layer manner at atomic-level precision on heterostructural substrates, opening up vast opportunities for unprecedented phenomena at the two-dimensional (2D) oxide interfaces. The emergence of a conductive interface between the two band insulators, LaAlO3 (LAO) and SrTiO3 (STO), represents the most celebrated exemplification in this context. Up to the date, a plethora of unexpected properties have been established at oxide heterointerfaces, ranging from 2D electron gas, 2D superconductivity, 2D orbital reconstruction to 2D magnetic ordering. However, why can the oxide interfaces be so surprising? This remains an outstanding problem to be addressed promptly. In this Talk, I will elucidate on how we disentangled the puzzle using simultaneous scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS) tackling of charge, lattice, and electronic-structure degrees of freedom, atom-by-atom and unit-cell-by-unit-cell. The localization of a 2D electron density at an insulating (Nd,Sr)MnO3/STO interface [PRB, 2013], the condensation of the 2D interfacial charges in (Nd,Sr)MnO3/STO into one-dimensional electron chains [Nature Commun., 2014], and hidden lattice instabilities as the origin of the conductive LAO/STO interface [Nature Commun., 2016] were readily resolved. Perspectives on 2D oxide-interfacial phenomena and STEM-EELS instrumentations will also be discussed.


Keywords: oxide interfaces, scanning transmission electron microscopy, electron energy-loss spectroscopy