二维铁电体中的Berezinskiii-Kosterlitz无磁相
Berezinskii-Kosterlitz-Thouless Phase in Two-dimensional Ferroelectrics
摘要：
著名的Berezinskiii-Kosterlitz-无相变（BKT）相变指的是拓扑转变，其特征在于，例如，通过在二维（2D）系统中涡旋-反涡旋对的解离。这种不寻常的相已经在各种类型的材料中报道过，但从未在由一个晶胞厚度（1UC）铁电体（也被称为2D铁电体）制成的新系统中报道过。在这里，使用基于第一原理的有效哈密顿方法导致发现存在于1UC锡碲的铁电和顺电状态之间的BKT相的许多指纹被完全放松。此外，外延应变被发现有显着的后果，这样的BKT相的温度范围为1UC SnTe。因此，我们的预测将BKT理论的范围扩展到一类新型功能材料，并证明应变是改变BKT特征的有效工具。
英文摘要：
The celebrated Berezinskii-Kosterlitz-Thouless (BKT) phase transition refers to a topological transition characterized, e.g., by the dissociation of vortex-antivortex pairs in two-dimensional (2D) systems. Such unusual phase has been reported in various types of materials, but never in the new class of systems made by one-unit-cell-thick (1UC) ferroelectrics (also coined as 2D ferroelectrics). Here, the use of a first-principles-based effective Hamiltonian method leads to the discovery of many fingerprints of a BKT phase existing in-between the ferroelectric and paraelectric states of 1UC tin tellurium being fully relaxed. Moreover, epitaxial strain is found to have dramatic consequences on the temperature range of such BKT phase for the 1UC SnTe. Consequently, our predictions extend the playground of BKT theory to a novel class of functional materials, and demonstrate that strain is an effective tool to alter BKT characteristics there.
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