School of Materials Science and Engineering, University of New South Wales Sydney, Kensington, NSW, Australia.
Center of Electron Microscopy, School of Materials Science and Engineering, State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou, Zhejiang, China.
Nat Commun. 2023 Jul 13;14(1):4178. doi: 10.1038/s41467-023-39841-3.
In ferroelectrics, complex interactions among various degrees of freedom enable the condensation of topologically protected polarization textures. Known as ferroelectric solitons, these particle-like structures represent a new class of materials with promise for beyond-CMOS technologies due to their ultrafine size and sensitivity to external stimuli. Such polarization textures have scarcely been demonstrated in multiferroics. Here, we present evidence for ferroelectric solitons in (BiFeO)/(SrTiO) superlattices. High-resolution piezoresponse force microscopy and Cs-corrected high-angle annular dark-field scanning transmission electron microscopy reveal a zoo of topologies, and polarization displacement mapping of planar specimens reveals center-convergent/divergent topological defects as small as 3 nm. Phase-field simulations verify that some of these structures can be classed as bimerons with a topological charge of ±1, and first-principles-based effective Hamiltonian computations show that the coexistence of such structures can lead to non-integer topological charges, a first observation in a BiFeO-based system. Our results open new opportunities in multiferroic topotronics.
在铁电体中，各种自由度之间的复杂相互作用使得拓扑保护的极化纹理得以凝聚。这些类粒子结构被称为铁电孤子，是一类新的材料，由于其超精细的尺寸和对外界刺激的敏感性，有望应用于超越 CMOS 的技术。在多铁体中，这种极化纹理几乎没有被证明过。在这里，我们在(BiFeO)/(SrTiO)超晶格中提供了铁电孤子的证据。高分辨率压电力显微镜和 Cs 校正的高角度环形暗场扫描透射电子显微镜揭示了一系列拓扑结构，平面样品的极化位移映射显示出中心会聚/发散拓扑缺陷，尺寸小至 3nm。相场模拟验证了其中一些结构可以归类为具有 ±1 拓扑电荷的双极化子，基于第一性原理的有效哈密顿量计算表明，这种结构的共存可能导致非整数拓扑电荷，这在基于 BiFeO 的系统中是首次观察到。我们的结果为多铁拓扑电子学开辟了新的机会。
