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The origin of 2EDG and magnetism at LaAlO3/SrTiO3 interface

Speaker: 
Ming Yang (CA2DM & IMRE, Singapore)
Date: 
Wed, 17/06/2015 - 11:00am to 12:00pm
Location: 
Physics Conference Room (S13-M01-11)
Event Type: 
Seminars

Abstract

The interface of dissimilar oxide materials hosts rich varieties of exotic phenomena not found in its constituent materials and has attracted a tremendous amount of research interests, both for fundamental physics and practical applications. An ideal example is the interface of two different non-magnetic insulators, polar LaAlO3 on nonpolar SrTiO3. Remarkably, conducting interface was observed with a step function insulator-metal transition at four LaAlO3 unit cells on SrTiO3, as well as unexpected interfacial magnetism. The mechanisms responsible for these remain controversial. Here, using density functional theory calculations and x-ray photoemission spectroscopy, we establish that the interplay of electronic reconstructions, surface oxygen vacancies, and lattice distortions fully compensates the polarization potential divergence in LaAlO3/SrTiO3, explaining naturally the experimental observations. While lattice distortions play a dominant role in insulating state, a spontaneous appearance of 1/4 oxygen vacancies per AlO2 sub-layer at the LaAlO3 surface accompanied by 0.5e- charge- transfer into the interface is responsible for interface conductivity and the discontinuous transition in LaAlO3/SrTiO3. In addition, we also found that surface oxygen vacancies contribute to the formation of weak interfacial magnetism in LaAlO3/SrTiO3 prepared at low oxygen partial pressure. In contrast, the strong magnetism in LaAlO3/SrTiO3 prepared at high oxygen partial pressure is due to interfacial cationic intermixing at the presence of surface oxygen vacancies.

About the speaker

Ming Yang obtained his Ph. D degree in Physics at the National University of Singapore, and then worked at NUS as postdoctoral research fellow before joining the Institute of Materials Research and Engineering, Singapore. His research interests are in condensed matter physics and materials physics at nanoscale, focusing mainly on understanding and predicting electronic, optical, and magnetic properties at the surface and interface of semiconductors, oxides, and two-dimensional materials by using first-principles calculations and spectroscopic techniques.

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