Hidden lattice instabilities as origin of the conductive interface between insulating LaAlO3 and SrTiO3

P. W. Lee, V. N. Singh, G. Y. Guo (), H.-J. Liu, J.-C. Lin, Y.-H. Chu (), C. H. Chen and M.-W. Chu ()
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P. W. Lee: National Taiwan University
V. N. Singh: National Taiwan University
G. Y. Guo: National Taiwan University
H.-J. Liu: National Chiao Tung University
J.-C. Lin: Institute of Physics, Academia Sinica
Y.-H. Chu: National Chiao Tung University
C. H. Chen: Center for Condensed Matter Sciences, National Taiwan University
M.-W. Chu: Center for Condensed Matter Sciences, National Taiwan University

Nature Communications, 2016, vol. 7, issue 1, 1-8

Abstract: Abstract The metallic interface between insulating LaAlO3 and SrTiO3 opens up the field of oxide electronics. With more than a decade of researches on this heterostructure, the origin of the interfacial conductivity, however, remains unsettled. Here we resolve this long-standing puzzle by atomic-scale observation of electron-gas formation for screening hidden lattice instabilities, rejuvenated near the interface by epitaxial strain. Using atomic-resolution imaging and electron spectroscopy, the generally accepted notions of polar catastrophe and cation intermixing for the metallic interface are discounted. Instead, the conductivity onset at the critical thickness of 4-unit cell LaAlO3 on SrTiO3 substrate is accompanied with head-to-head ferroelectric-like polarizations across the interface due to strain-rejuvenated ferroelectric-like instabilities in the materials. The divergent depolarization fields of the head-to-head polarizations cast the interface into an electron reservoir, forming screening electron gas in SrTiO3 with LaAlO3 hosting complementary localized holes. The ferroelectric-like polarizations and electron–hole juxtaposition reveal the cooperative nature of metallic LaAlO3/SrTiO3.

Date: 2016
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DOI: 10.1038/ncomms12773

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