Wang Le, Yang Zhifei, Koirala Krishna Prasad, Bowden Mark E, Freeland John W, Sushko Peter V, Kuo Cheng-Tai, Chambers Scott A, Wang Chongmin, Jalan Bharat, Du Yingge
Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA 99354, USA.
Department of Chemical Engineering and Materials Science, University of Minnesota-Twin Cities, Minneapolis, MN 55455, USA.
Sci Adv. 2024 Dec 20;10(51):eadq6687. doi: 10.1126/sciadv.adq6687. Epub 2024 Dec 18.
Charge transfer or redistribution at oxide heterointerfaces is a critical phenomenon, often leading to remarkable properties such as two-dimensional electron gas and interfacial ferromagnetism. Despite studies on LaNiO/LaFeO superlattices and heterostructures, the direction and magnitude of the charge transfer remain debated, with some suggesting no charge transfer due to the high stability of Fe (3d). Here, we synthesized a series of epitaxial LaNiO/LaFeO superlattices and demonstrated partial (up to ~0.5 e/interface unit cell) charge transfer from Fe to Ni near the interface, supported by density functional theory simulations and spectroscopic evidence of changes in Ni and Fe oxidation states. The electron transfer from LaFeO to LaNiO and the subsequent rearrangement of the Fe 3d band create an unexpected metallic ground state within the LaFeO layer, strongly influencing the in-plane transport properties across the superlattice. Moreover, we establish a direct correlation between interfacial charge transfer and in-plane electrical transport properties, providing insights for designing functional oxide heterostructures with emerging properties.
氧化物异质界面处的电荷转移或重新分布是一种关键现象，常常会导致诸如二维电子气和界面铁磁性等显著特性。尽管对LaNiO/LaFeO超晶格和异质结构已有研究，但电荷转移的方向和大小仍存在争议，一些研究认为由于Fe（3d）的高稳定性，不存在电荷转移。在此，我们合成了一系列外延LaNiO/LaFeO超晶格，并通过密度泛函理论模拟以及Ni和Fe氧化态变化的光谱证据，证明了在界面附近存在从Fe到Ni的部分（高达约0.5 e/界面晶胞）电荷转移。从LaFeO到LaNiO的电子转移以及随后Fe 3d能带的重新排列在LaFeO层内产生了意想不到的金属基态，强烈影响了整个超晶格的面内输运性质。此外，我们建立了界面电荷转移与面内电输运性质之间的直接关联，为设计具有新兴特性的功能性氧化物异质结构提供了思路。
