PbTiO $_3$ / SrTiO $_3$界面二维电子气的从头算研究
Two-dimensional electron gas at the PbTiO$_3$/SrTiO$_3$ interface: an ab initio study
摘要：
在极性突变的情况下，极性不连续占的驱动力形成的二维电子气（2DEG）在极性和非极性绝缘体之间的界面。在本文中，我们用铁电薄膜代替通常的非铁电极性材料，并使用铁电极化作为极性不连续性的来源。我们采用从头计算方法系统地研究了PbTiO $_3$ /SrTiO $_3$异质结构中二维自由载流子气体的稳定性、形成和性质。在临界厚度以上，由于自由载流子提供的静电屏蔽，铁电层可以稳定在面外单畴结构中。我们的模拟还预测，该系统可以在三个稳定的配置（极化向上，向下或零）之间切换，允许非易失性操纵的自由电荷密度和符号的接口。此外，铁电极化和自由电荷密度之间的联系表明，我们的分析构成了令人信服的支持极性突变模型，用于合理化的形成2DEG在氧化物界面。
英文摘要：
In the polar catastrophe scenario, polar discontinuity accounts for the driving force of the formation of a two-dimensional electron gas (2DEG) at the interface between polar and non-polar insulators. In this paper, we substitute the usual, non-ferroelectric, polar material with a ferroelectric thin film and use the ferroelectric polarization as the source for polar discontinuity. We use ab initio simulations to systematically investigate the stability, formation and properties of the two-dimensional free-carrier gases formed in PbTiO$_3$/SrTiO$_3$ heterostructures under realistic mechanical and electrical boundary conditions. Above a critical thickness, the ferroelectric layers can be stabilized in the out-of-plane monodomain configuration due to the electrostatic screening provided by the free-carriers. Our simulations also predict that the system can be switched between three stable configurations (polarization up, down or zero), allowing the non-volatile manipulation of the free charge density and sign at the interface. Furthermore, the link between ferroelectric polarization and free charge density demonstrated by our analysis constitutes compelling support for the polar catastrophe model that is used to rationalize the formation of 2DEG at oxide interfaces.
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