Oxide heterostructures have attracted a lot of interest because of their rich exotic phenomena and potential applications. Recently, a greatly enhanced tunneling electroresistance (TER) of ferroelectric tunnel junctions (FTJs) has been realized in such heterostructures. However, our understanding on the electronic structure of resistance response with polarization reversal and the origin of huge TER is still lacking. Here, we report on electronic structures, particularly at the interface and surface, and the control of the spontaneous polarization of BaTiO3 films by changing the termination of a SrTiO3 substrate. Interestingly, unusual electron and hole midgap states are concurrently formed and accompanied by orbital reconstructions, which determine the ferroelectric polarization orientation in the BaTiO3/SrTiO3. Such unusual midgap states, which yield a strong electronic screening effect, reduce the ferroelectric barrier width and height, and pin the ferroelectric polarization, lead to a dramatic enhancement of the TER effect. The midgap states are also observed in BaTiO3 films on electron-doped Nb/SrTiO3 revealing its universality. Our result provides new insight into the origin of the huge TER effect and opens a new route for designing ferroelectric tunnel junction-based devices with huge TER through interface engineering.

中文翻译：

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BaTiO3 / SrTiO3中异常的空穴和电子能隙状态以及轨道重构引起巨大的铁电隧穿电阻。

氧化物异质结构因其丰富的奇异现象和潜在的应用而吸引了很多兴趣。近来，已经在这种异质结构中实现了铁电隧道结（FTJ）的大大增强的隧道电阻（TER）。然而，我们对极化反转的电阻响应的电子结构以及巨大的TER的起源仍然缺乏了解。在这里，我们报告了电子结构，特别是在界面和表面的电子结构，以及通过改变SrTiO3基板的端接来控制BaTiO3薄膜的自发极化的信息。有趣的是，异常的电子和空穴的中间能隙状态同时形成并伴随着轨道重构，这决定了BaTiO3 / SrTiO3中的铁电极化取向。这种异常的中间间隙状态 其产生强的电子屏蔽效果，减小铁电势垒的宽度和高度，并钉住铁电极化，从而导致TER效应显着增强。在电子掺杂的Nb / SrTiO3上的BaTiO3薄膜中也观察到了中间能隙状态，揭示了其通用性。我们的结果为巨大TER效应的起源提供了新的见解，并为通过接口工程设计具有巨大TER的铁电隧道结型器件开辟了一条新途径。