Novoselov K S, Geim A K, Dubonos S V, Hill E W, Grigorieva I V
Department of Physics, University of Manchester, Manchester M13 9PL, UK.
Nature. 2003 Dec 18;426(6968):812-6. doi: 10.1038/nature02180.
The discrete nature of crystal lattices plays a role in virtually every material property. But it is only when the size of entities hosted by a crystal becomes comparable to the lattice period--as occurs for dislocations, vortices in superconductors and domain walls--that this discreteness is manifest explicitly. The associated phenomena are usually described in terms of a background Peierls 'atomic washboard' energy potential, which was first introduced for the case of dislocation motion in the 1940s. This concept has subsequently been invoked in many situations to describe certain features in the bulk behaviour of materials, but has to date eluded direct detection and experimental scrutiny at a microscopic level. Here we report observations of the motion of a single magnetic domain wall at the scale of the individual peaks and troughs of the atomic energy landscape. Our experiments reveal that domain walls can become trapped between crystalline planes, and that they propagate by distinct jumps that match the lattice periodicity. The jumps between valleys are found to involve unusual dynamics that shed light on the microscopic processes underlying domain-wall propagation. Such observations offer a means for probing experimentally the physics of topological defects in discrete lattices--a field rich in phenomena that have been subject to extensive theoretical study.
晶格的离散性质几乎在每种材料特性中都发挥着作用。但只有当晶体所容纳的实体尺寸与晶格周期可比时——位错、超导体中的涡旋以及畴壁的情况就是如此——这种离散性才会明显地表现出来。相关现象通常根据背景皮尔斯“原子搓衣板”能量势来描述，该能量势在20世纪40年代首次针对位错运动的情况被引入。这个概念随后在许多情况下被用来描述材料体行为中的某些特征，但迄今为止在微观层面上仍未得到直接检测和实验审视。在此，我们报告了在单个磁畴壁在原子能量景观的各个峰谷尺度上运动的观测结果。我们的实验表明，畴壁可能被困在晶面之间，并且它们通过与晶格周期性相匹配的明显跳跃来传播。发现谷间跳跃涉及不同寻常的动力学，这为畴壁传播背后的微观过程提供了线索。此类观测为实验探测离散晶格中拓扑缺陷的物理性质提供了一种手段——这是一个现象丰富且已进行广泛理论研究的领域。
