Ferroelectric, Ferroelastic and Multiferroic Domain Walls: a New Horizon in Nanoscale Functional Materials

一些功能材料，如铁电材料，含有被称为“磁区壁”的膜或片状结构。几十年来，域壁被认为是微不足道的微结构组件，意义不大。现在很明显，没有什么比真相更离谱的了。事实上，域壁往往具有与其周围的域完全不同的独特功能特性：当其余材料绝缘时，它们可以是导体或超导体；它们可以在非磁性晶体中显示磁性秩序，当它们周围的基质非极性时，它们可以具有排列的电偶极子。实际上，域壁代表了一类新的片状纳米功能材料。对这种新的片状材料家族的行为有一个基本的了解，它已经显示了非常广泛的性质，这当然是值得的，但区域墙提供了更多：独特的，它们在空间上是可移动的，可以从一个点到另一个点可控地分流，可以自发地创造，或者让它们消失。这种独特的“现在你看到它，现在你不会看到它”的动态特性可能会从根本上改变我们思考将功能材料集成到设备中的方式以及启用设备功能的方式：功能活跃的域壁本身可以作为设备操作的主要机制被引入或移除。作为一个简单的例子，可以容易地设想一种新形式的晶体管，其中通过分别注入和湮灭连接源极和漏极的导电磁区壁沟道来实现在“开”和“关”状态之间的切换。根据引入的导电壁的数量，多个受控磁区壁注入事件(例如，由于源极和漏极之间的电偏压中的顺序脉冲引起)可以产生一系列不同的电阻状态。因此，可以创造出一种新型的忆阻器装置。未来基于域名墙的应用的可能性是诱人的。然而，相关研究仍处于早期阶段；需要做大量工作来建立域壁功能行为的基本物理，并且需要开发策略以使其能够以纳米级的精度可靠地部署。只有到那时，才能适当地评估基于磁区墙的设备的潜力。在这项关键的质量拨款中，我们寻求利用一些世界级的英国学术团队(剑桥、圣安德鲁斯、沃里克和贝尔法斯特)的合作努力，来探索新的功能活跃的铁电、铁弹性和多铁性磁区墙。我们将共同努力：(I)对已知功能活跃的域壁系统的属性产生急需的新的基本见解；(Ii)对新的功能活跃的域壁系统进行智能搜索；(Iii)展示简单的电子和热器件(晶体管、忆阻器和智能热传输芯片)，其中域壁特性是设备性能的关键，并因此评估更广泛的基于域壁的应用的潜力。

Some functional materials, such as ferroelectrics, contain membrane or sheet structures called "domain walls". For decades, domain walls were dismissed as being minor microstructural components of little significance. It is now clear that nothing could be further from the truth. Domain walls often, in fact, have unique functional properties that are completely different from the domains that they surround: they can be conductors or superconductors when the rest of the material is insulating; they can display magnetic order in non-magnetic crystals and they can possess aligned electrical dipoles when the matrix surrounding them is non-polar. In effect, domain walls represent a new class of sheet-like nanoscale functional material. Gaining a basic understanding of the behaviour of such a new family of sheet materials, which already shows a very wide gamut of properties, is certainly worthwhile, but domain walls offer so much more: uniquely, they are spatially mobile, can be controllably shunted from point to point, and can be spontaneously created, or made to disappear. This unique "now-you-see-it, now-you-don't" dynamic property could radically alter the way in which we think about the integration of functional materials into devices and the way in which device functionality is enabled: functionally active domain walls themselves could be introduced or removed as the primary mechanism in device operation. As a simple example, a new form of transistor could readily be envisaged where switching between the "ON" and "OFF" states is achieved through the injection and annihilation respectively of conducting domain wall channels connecting the source and drain electrodes. Multiple controlled domain wall injection events (resulting from sequential pulses in electrical bias between source and drain, for example) could create a series of different resistance states, depending on the number of conducting walls introduced. Thus a new kind of memristor device could be created. Possibilities for future domain wall-based applications are tantalising. However, relevant research is still at an early stage; a great deal needs to be done to establish the basic physics of the functional behavior of domain walls and strategies need to be developed to allow their reliable deployment with nanoscale precision. Only then can the potential for domain wall based devices be properly assessed.In this Critical Mass Grant, we seek to harness the collaborative effort of a number of world-class UK-based academic teams (in Cambridge, St. Andrews, Warwick and Belfast) to explore novel functionally active ferroelectric, ferroelastic and multiferroic domain walls. Together, we will: (i) Generate badly needed new and fundamental insight into the properties of known functionally active domain wall systems;(ii) Perform smart searches for new functionally active domain wall systems;(iii) Demonstrate simple electronic and thermal devices (transistors, memristors and smart heat transfer chips) in which domain wall properties are the key to device performance and hence assess the potential for wider domain wall-based applications.