Order by disorder in the antiferromagnetic Ising model on an elastic triangular lattice
Order by disorder in the antiferromagnetic Ising model on an elastic triangular lattice
复制标题
弹性三角晶格反铁磁 Ising 模型中的无序排序
DOI：
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发表时间：
2010
影响因子：
11.1
通讯作者：
T. Lubensky
中科院分区：
文献类型：
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作者：
Y. Shokef;A. Souslov;T. Lubensky
几何受挫的材料具有基态简并，这种简并可以通过微妙的效应来解除，例如高阶相互作用导致有序结构的小能量偏好。或者，有序可以由构型之间的熵差异导致，这种效应被称为按无序排序。基于最近在受挫胶体体系中的实验，我们考虑了可变形三角晶格上的反铁磁性伊辛模型，在该体系中，有序可能是由熵引起的。我们在微观水平上精确地计算了位移，并且与以前的研究相反，发现了一个随机之字形条纹的部分无序基态。每个这样的组态都有不同的形变，因此有一个独特的具有不同熵的声子谱，消除了有限温度下的简并。尽管如此，由于基态组态之间的自由能垒，系统进入了无序的玻璃态。
Geometrically frustrated materials have a ground-state degeneracy that may be lifted by subtle effects, such as higher-order interactions causing small energetic preferences for ordered structures. Alternatively, ordering may result from entropic differences between configurations in an effect termed order by disorder. Motivated by recent experiments in a frustrated colloidal system in which ordering is suspected to result from entropy, we consider in this paper the antiferromagnetic Ising model on a deformable triangular lattice. We calculate the displacements exactly at the microscopic level and, contrary to previous studies, find a partially disordered ground state of randomly zigzagging stripes. Each such configuration is deformed differently and thus has a unique phonon spectrum with distinct entropy, lifting the degeneracy at finite temperature. Nonetheless, due to the free-energy barriers between the ground-state configurations, the system falls into a disordered glassy state.