Min Taewon, Choi Wooseon, Seo Jinsol, Han Gyeongtak, Song Kyung, Ryu Sangwoo, Lee Hyungwoo, Lee Jungwoo, Eom Kitae, Eom Chang-Beom, Jeong Hu Young, Kim Young-Min, Lee Jaekwang, Oh Sang Ho
Department of Physics, Pusan National University, Busan 46241, Republic of Korea.
Department of Energy Science, Sungkyunkwan University, Suwon 16419, Republic of Korea.
Sci Adv. 2021 Apr 21;7(17). doi: 10.1126/sciadv.abe9053. Print 2021 Apr.
Polarity discontinuity across LaAlO/SrTiO (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 ( ) and disappear simultaneously above with the formation of 2DEG. Electron energy-loss spectroscopy and density functional theory (DFT) calculations provide direct evidence of oxygen vacancy ( ) 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 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.
跨越LaAlO₃/SrTiO₃（LAO/STO）异质结构的极性不连续性会引发电子重构，其中涉及二维电子气（2DEG）的形成以及以反铁电畸变（AFD）旋转和铁电（FE）畸变表征的结构畸变。我们表明，AFD和FE模式在LAO/STO（111）异质结构中协同耦合；它们在临界厚度以下共存，在临界厚度以上随着2DEG的形成而同时消失。电子能量损失谱和密度泛函理论（DFT）计算提供了LAO（111）表面氧空位形成的直接证据，氧空位是2DEG的来源。追踪LAO的AFD旋转和FE畸变发现，它们的演化与氧空位分布密切相关。本研究表明，氧化物异质结构中的AFD和FE模式是失配应变和极性场相互作用的结果，并且进一步表明，通过改变界面取向，可以将它们的组合调整为竞争或协同耦合。
