Impact of strain-field interference on the coexistence of electron and hole gases in SrTiO3/LaAlO3/SrTiO3
Journal
Physical Review Materials
Journal Volume
3
Journal Issue
7
Pages
075003-1 - 075003-10
Date Issued
2019
Author(s)
Abstract
The renowned two-dimensional electron gas at the interface of insulating LaAlO3 and SrTiO3 poses a grand challenge in engineering the hole counterpart and its coexistence with the electron gas. The room-temperature realization of such coexisting states was recently achieved in the SrTiO3-capped LaAlO3/SrTiO3, and the electron and hole gases in the SrTiO3/LaAlO3/SrTiO3 reside at the respective bottom and top interfaces, which are separated by a few tens of the interlayer-LaAlO3 unit cells. What happens if the two interfaces are brought to the extreme proximity of just a few lattices away? Using atomic-resolution electron microscopy and spectroscopy, we tackled this problem in SrTiO3/LaAlO3/SrTiO3 with LaAlO3 of 3 and 5 unit cells, respectively. Notably, both SrTiO3/LaAlO3/SrTiO3 heterostructures are dominated by electron conductivity at room temperature. The microscopic evaluation at picometer accuracy unveils head-to-head (tail-to-head) ferroelectriclike polarizations across the bottom (top) interface, in comparison to the established notion of characteristic strain-induced head-to-head polarizations in primitive metallic LaAlO3/SrTiO3 that form a potential well and confine the accompanied screening electrons into two-dimensional electron gas. The atomic-scale spectral investigation of the SrTiO3/LaAlO3/SrTiO3 reveals the unexpected depletion (resurrection) of electrons at the head-to-head bottom (tail-to-head top) interface and the LaAlO3 hosts coexisting localized electrons and holes, casting an electric field with tens of meV/Å and serving as the depolarization field to the LaAlO3 dipole. The landscape of the SrTiO3/LaAlO3/SrTiO3 turns out to be the polarity-neutral LaAlO3 sandwiched by the head-to-head SrTiO3 polarizations, with the potential gradient due to the unbalanced polarizations pointing to the top interface and resurrecting the screening electrons thereby. The dominant electron conductivity in the thin SrTiO3/LaAlO3/SrTiO3 is profoundly related to this polarization pattern and the intricate strain-field interference across the two closely spaced interfaces, accounting for the pattern onset, was atomically revealed. © 2019 American Physical Society.
Subjects
Aluminum compounds; Electric fields; Electrons; Gases; Interface states; Lanthanum compounds; Petroleum reservoir evaluation; Phase interfaces; Polarization; Strontium titanates; Two dimensional electron gas; Atomic-resolution electron microscopies; Co-existing state; Depolarization fields; Electron conductivity; Localized electrons; Microscopic evaluation; Polarization patterns; Potential gradients; Titanium compounds
SDGs
Other Subjects
Aluminum compounds; Electric fields; Electrons; Gases; Interface states; Lanthanum compounds; Petroleum reservoir evaluation; Phase interfaces; Polarization; Strontium titanates; Two dimensional electron gas; Atomic-resolution electron microscopies; Co-existing state; Depolarization fields; Electron conductivity; Localized electrons; Microscopic evaluation; Polarization patterns; Potential gradients; Titanium compounds
Publisher
American Physical Society
Type
journal article