Enhanced in-plane ferroelectricity, antiferroelectricity, and unconventional 2D emergent fermions in quadruple-layer XSbO2 (X = Li, Na)
Enhanced in-plane ferroelectricity, antiferroelectricity, and unconventional 2D emergent fermions in quadruple-layer XSbO2 (X = Li, Na)
复制标题
四层 XSbO2 (X = Li, Na) 中增强的面内铁电性、反铁电性和非常规二维涌现费米子
DOI：
10.1039/d1nr06051a
复制
发表时间：
2021
期刊：
影响因子：
6.7
通讯作者：
Liu Chang
中科院分区：
文献类型：
--
作者：
Guan Shan;Zhang GuangBiao;Liu Chang
低维铁电性和具有带交叉保护的狄拉克材料是一个令人感兴趣的研究课题。基于第一性原理计算，我们预测了在动力学稳定的四层（QL）XSbO 2（X = Li，Na）中自发的面内极化和新的二维出射费米子的共存. QL-XSbO 2在不同的极化结构下，可以表现出非常规的内QL铁电性和反铁电性。两个基态都具有强大的铁电性，QL-LiSbO 2和QL-NaSbO 2的自发极化分别为0.56 nC m−1和0.39 nC m−1。有趣的是，QL-LiSbO 2具有两个其他亚稳铁电（FE）相。接地FE相可以灵活地驱动到两个亚稳FE相之一，然后进入反铁电（AFE）相。在这个相变过程中，出现了几种类型的二维费米子，例如，沙漏混合和II型外尔环在地面FE阶段，II型外尔费米子在亚稳态FE阶段，和II型狄拉克费米子在AFE阶段。这些2D费米子在自旋轨道耦合下是稳健的。值得注意的是，其中两个费米子，例如，沙漏混合或II型外尔环，以前没有观察到。我们的研究结果确定QL-XSbO 2作为一个独特的平台，研究二维铁电性相关的二维紧急费米子。
Low-dimensional ferroelectricity and Dirac materials with protected band crossings are fascinating research subjects. Based on first-principles calculations, we predict the coexistence of spontaneous in-plane polarization and novel 2D emergent fermions in dynamically stable quadruple-layer (QL) XSbO2 (X = Li, Na). Depending on the different polarization configurations, QL-XSbO2 can exhibit unconventional inner-QL ferroelectricity and antiferroelectricity. Both ground states harbor robust ferroelectricity with enhanced spontaneous polarization of 0.56 nC m−1 and 0.39 nC m−1 for QL-LiSbO2 and QL-NaSbO2, respectively. Interestingly, the QL-LiSbO2 possesses two other metastable ferroelectric (FE) phases. The ground FE phase can be flexibly driven into one of the two metastable FE phases and then into the antiferroelectric (AFE) phase. During this phase transition, several types of 2D fermions emerge, for instance, hourglass hybrid and type-II Weyl loops in the ground FE phase, type-II Weyl fermionsin the metastable FE phase, and type-II Dirac fermions in the AFE phase. These 2D fermions are robust under spin–orbit coupling. Notably, two of these fermions, e.g., an hourglass hybrid or type-II Weyl loop, have not been observed before. Our findings identify QL-XSbO2 as a unique platform for studying 2D ferroelectricity relating to 2D emergent fermions.