The Topology of Conductive Ferroelectric Domain Walls

铁电体中的畴壁由于其优异的介电、光学、磁学、电学和机械性能，在过去的10年里成为人们关注的热点。DW代表纳米界面，其延伸穿过整个体系统，并显示超高的电子电导率，对于体单晶LiNbO3（LNO）中的单个DW达到几个10 µA。这些优异的性能使得铁电DWs成为最有前途的功能纳米结构之一，可用于纳米电子器件中的现代型和可重构应用。根据最近的研究，铁电DW在其介电极化中可能包含比Ising型配置复杂得多的新颖拓扑结构，Ising型配置是传统上预期的单轴铁电体中的DW类型。DW处的局部对称性破坏是特别重要的，因为它可以促进奇异的极性拓扑结构，类似于在磁性系统中观察到的那些。探索铁电DW的详细铁电结构是理解和控制DW性能的先决条件。这个联合研究项目的目标是阐明在这样的DW区域的局部对称性和拓扑结构，并调查和量化其相互关联的物理和光学特性时，呈现出高度conductively.The两个团队结盟在这个联合德法项目已经表明，DW可以优雅地调整为传输高电子电流沿着二维DW。在LNO中，可以通过简单地改变DW相对于极轴的倾斜来操纵这样的壁内的自由电荷载流子密度。然后，我们期望该DW从其纯伊辛型配置转换为布洛赫或尼尔型状态，这取决于所研究的材料、可能的样品掺杂或施加在晶体上的电偏置场。此外，我们还开发了复杂的局部探测和非线性光学技术，能够量化和三维映射此类非伊辛配置的存在。因此，我们打算在LNO单晶家族中设计具有和不具有Mg掺杂的手性DW，并使用例如二次谐波产生偏振法在真实的时间和真实的空间中监测它们的行为。该项目预计将对DW中这种非伊辛（通常是手征）极化结构的起源和建立提供开创性的见解，这对于深入理解和调整基于铁电DW的未来光电子纳米器件是必要的。

Domain walls (DWs) in ferroelectrics have become a topic of major interest over the last 10 years because of their exceptional dielectric, optical, magnetic, electronic and mechanical properties. The DWs represent nanometric interfaces that extend across the full bulk system and display an ultra-high electronic conductivity, reaching several 10 µA for a single DW in bulk single crystalline LiNbO3 (LNO). These remarkable properties propel ferroelectric DWs as one of the most promising functional nanostructure for modern-type and reconfigurable applications in nanoelectronic devices. According to recent studies, ferroelectric DWs could contain novel topological structures in their dielectric polarization that are much more complex than the Ising-type configuration, which is the traditionally expected DW type in uniaxial ferroelectrics. The local sym¬metry breaking at the DWs is particularly important as it can promote exotic polar topological structures, similar to those observed in magnetic systems. Exploring the detailed ferroic structure of ferroelectric DWs is a prerequisite for the understanding and control of DW properties. The goal of this joint research project is to elucidate the local symmetry and topology at such DW regions and to investigate and quantify their interrelated physical and optical properties when being rendered highly conductive.The two teams allied within this joint German-French project have shown that DWs can be elegantly tuned for transporting high electronic currents along the two-dimensional DW. In LNO, the free charge carrier density within such a wall can be steered by simply varying the DW’s inclination with respect to the polar axes. We then expect this DW to convert from its pure Ising-type configuration into a Bloch- or Néel-type state, depending on both the material under investigation, a possible sample doping, or an electrical bias field applied across the crystal. In addition, we have developed sophisticated local probe and nonlinear optical techniques that are able to quantify and three-dimensionally map the presence of such non-Ising configurations. We accordingly intend to engineer chiral DWs in the LNO single crystals family, both with and without Mg doping, and monitor their behavior in real time and real space using, for instance, second-harmonic generation polarimetry. This project is expected to deliver groundbreaking insight on the origin and build-up of such non-Ising, often chiral polarization structures at DWs, as is necessary for the profound understanding and tuning of future optoelectronic nano-devices based on ferroelectric DWs.