Cooperative evolution of polar distortion and nonpolar rotation of oxygen octahedra in oxide heterostructures.
basic_science · Level V
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- Record sourced from PubMed, PMID 33883134.
- Also identified by DOI 10.1126/sciadv.abe9053 and PMC identifier 8059930.
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Abstract
Polarity discontinuity across LaAlO<sub>3</sub>/SrTiO<sub>3</sub> (LAO/STO) heterostructures induces electronic reconstruction involving the formation of two-dimensional electron gas (2DEG) and structural distortions characterized by antiferrodistortive (AFD) rotation and ferroelectric (FE) distortion. We show that AFD and FE modes are cooperatively coupled in LAO/STO (111) heterostructures; they coexist below the critical thickness (<i>t</i> <sub>c</sub>) and disappear simultaneously above <i>t</i> <sub>c</sub> with the formation of 2DEG. Electron energy-loss spectroscopy and density functional theory (DFT) calculations provide direct evidence of oxygen vacancy (<i>V</i> <sub>O</sub>) formation at the LAO (111) surface, which acts as the source of 2DEG. Tracing the AFD rotation and FE distortion of LAO reveals that their evolution is strongly correlated with <i>V</i> <sub>O</sub> distribution. The present study demonstrates that AFD and FE modes in oxide heterostructures emerge as a consequence of interplay between misfit strain and polar field, and further that their combination can be tuned to competitive or cooperative coupling by changing the interface orientation.