We employed first-principles to delve into the strain-induced structural phase transitions in epitaxial LaTaO₄ films. The ground state of bulk LaTaO₄ adopts a monoclinic antiferroelectric phase, characterized by the antiphase rotation of two adjacent oxygen octahedra layers. Under epitaxial tensile strain, LaTaO₄ thin films undergo a consecutive phase transition, namely, antiferroelectric–ferroelectric–antiferroelectric phase transitions. The ferroelectricity in the orthorhombic phase under tensile strain originates from the in-phase rotation of two adjacent oxygen octahedra layers, in contrast to the case of perovskite systems, in which octahedra rotation suppresses the conventional proper ferroelectricity. With spin–orbit coupling effects, a pronounced Rashba effect at the Brillouin zone center naturally leads to the formation of opposite directions of spin texture. Moreover, the tensile strain also synergistically enhances the corresponding Rashba parameters. Our findings may provide novel insights for controlling oxygen octahedra rotation to achieve control over the ferroelectricity and Rashba effect, which holds promising implications for applications in electronics and spintronics.

中文翻译：

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外延 LaTaO4 薄膜中应变诱导的反铁电-铁电-反铁电相变


我们采用第一性原理深入研究了外延 LaTaO₄ 薄膜中应变诱导的结构相变。体体 LaTaO₄ 的基态采用单斜反铁电相，其特征是两个相邻氧八面体层的反相旋转。在外延拉伸应变下，LaTaO₄ 薄膜发生连续的相变，即反铁电-铁电-反铁电相变。在拉伸应变下，斜交相中的铁电性起源于两个相邻氧八面体层的同相旋转，这与钙钛矿系统的情况相反，在钙钛矿系统中，八面体旋转抑制了传统的适当铁电性。在自旋-轨道耦合效应下，布里渊区中心明显的 Rashba 效应自然会导致形成相反方向的自旋织构。此外，拉伸应变还协同增强了相应的 Rashba 参数。我们的研究结果可能为控制氧八面体旋转以实现对铁电性和 Rashba 效应的控制提供新的见解，这对电子学和自旋电子学中的应用具有广阔的意义。