Geometric Frustration in an Optical Superlattice

许多材料的结构是由材料的成分如何遵守微观物理原理建立的许多约束条件决定的。例如，稳定的晶体结构是那些被限制为最大限度地减少形成晶体的原子或分子之间的成对相互作用的结构。类似地，在磁性材料中，定位在邻近原子上的电子的磁矩可能会通过排列在相同或相反的方向来降低它们的能量。在某些情况下，不存在满足系统内所有能量约束的微不足道的方法，因此不可能形成系统的任何简单配置--例如，晶体结构中的磁矩。这种现象被称为挫折感。在受挫的系统中是否建立了某种可预测的秩序，如果是的话，这种秩序的性质是什么，这两个问题都是物理学中的重大悬而未决的问题。这些问题的答案与新材料的设计以及此类材料在信息技术和其他用途上的应用有关。在这个项目中，将使用被困在几何图案中的冷原子来探索受挫材料的物理学--例如二维Kagome晶格--这些原子导致了高度受挫。我们将研究这一挫折对相变和传输的影响。所选择的系统提供了几何挫折的干净实现，没有影响类似系统的固态实现的结构缺陷。因此，这些实验结果可能会为几何挫折等令人烦恼的问题提供明确的答案。

The structure of many materials is determined by how the constituents of the material obey the many constraints that are established by microscopic physical principles. For example, stable crystalline structures are those that are constrained to minimize the pairwise interactions between the atoms or molecules forming the crystal. Similarly, in magnetic materials, the magnetic moments of electrons that are localized on neighboring atoms may lower their energy either by aligning in the same or in opposite orientations. In some cases, there is no trivial way in which to satisfy all the energetic constraints within a system, and so the formation of any simple configuration of the system -- e.g. of magnetic moments within a crystalline structure -- is precluded. This phenomenon is known as frustration. The question of whether some sort of predictable order is established in frustrated systems, and, if so, what is the character of that order, are both major open questions in physics. The answer to these questions has relevance to the design of new materials and the application of such materials to information technology and other uses.In this project, the physics of frustrated materials will be explored using cold atoms that are trapped within geometric patterns -- such as the two-dimensional kagome lattice -- that lead to a high degree of frustration. The effects of this frustration on phase transitions and on transport will be investigated. The system chosen provides a clean realization of geometric frustration, free of the structural defects that influence solid-state realizations of similar systems. Thus, the experimental findings may provide clear answers to vexing questions regarding geometric frustration.