Hidden lattice instabilities as origin of the conductive interface between insulating LaAlO3 and SrTiO3.
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.
Department of Physics, National Taiwan University, Taipei 106, Taiwan.|Center for Condensed Matter Sciences, National Taiwan University, Taipei 106, Taiwan.
P W
PW
Lee
Department of Physics, National Taiwan University, Taipei 106, Taiwan.|Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan.
V N
VN
Singh
Department of Physics, National Taiwan University, Taipei 106, Taiwan.|Physics Division, National Center for Theoretical Sciences, Hsinchu 300, Taiwan.
G Y
GY
Guo
Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu 300, Taiwan.
H-J
HJ
Liu
Institute of Physics, Academia Sinica, Taipei 105, Taiwan.
J-C
JC
Lin
Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu 300, Taiwan.|Institute of Physics, Academia Sinica, Taipei 105, Taiwan.
Y-H
YH
Chu
Center for Condensed Matter Sciences, National Taiwan University, Taipei 106, Taiwan.|Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA.
C H
CH
Chen
Center for Condensed Matter Sciences, National Taiwan University, Taipei 106, Taiwan.
M-W
MW
Chu