Dimensionality Controlled Octahedral Symmetry-Mismatch and Functionalities in Epitaxial LaCoO3/SrTiO3 Heterostructures

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• 作者：Liang Qiao ; Jae Hyuck Jang ; David J. Singh ; Zheng Gai ; Haiyan Xiao ; Apurva Mehta ; Rama K. Vasudevan ; Alexander Tselev ; Zhenxing Feng ; Hua Zhou ; Sean Li ; Wilfrid Prellier ; Xiaotao Zu ; Zijiang Liu ; Albina Borisevich ; Arthur P. Baddorf ; Michael D. Biegalski
• 刊名：Nano Letters
• 出版年：2015
• 出版时间：July 8, 2015
• 年：2015
• 卷：15
• 期：7
• 页码：4677-4684
• 全文大小：456K
• ISSN：1530-6992

文摘

Epitaxial strain provides a powerful approach to manipulate physical properties of materials through rigid compression or extension of their chemical bonds via lattice-mismatch. Although symmetry-mismatch can lead to new physics by stabilizing novel interfacial structures, challenges in obtaining atomic-level structural information as well as lack of a suitable approach to separate it from the parasitical lattice-mismatch have limited the development of this field. Here, we present unambiguous experimental evidence that the symmetry-mismatch can be strongly controlled by dimensionality and significantly impact the collective electronic and magnetic functionalities in ultrathin perovskite LaCoO₃/SrTiO₃ heterojunctions. State-of-art diffraction and microscopy reveal that symmetry breaking dramatically modifies the interfacial structure of CoO₆ octahedral building-blocks, resulting in expanded octahedron volume, reduced covalent screening, and stronger electron correlations. Such phenomena fundamentally alter the electronic and magnetic behaviors of LaCoO₃ thin-films. We conclude that for epitaxial systems, correlation strength can be tuned by changing orbital hybridization, thus affecting the Coulomb repulsion, U, instead of by changing the band structure as the common paradigm in bulks. These results clarify the origin of magnetic ordering for epitaxial LaCoO₃ and provide a route to manipulate electron correlation and magnetic functionality by orbital engineering at oxide heterojunctions.