Hanakata Paul Z, Plummer Abigail, Nelson David R
Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA.
Phys Rev Lett. 2022 Feb 18;128(7):075902. doi: 10.1103/PhysRevLett.128.075902.
Motivated by efforts to create thin nanoscale metamaterials and understand atomically thin binary monolayers, we study the finite temperature statistical mechanics of arrays of bistable buckled dilations embedded in free-standing two-dimensional crystalline membranes that are allowed to fluctuate in three dimensions. The buckled nodes behave like discrete, but highly compressible, Ising spins, leading to a phase transition at T_{c} with singularities in the staggered "magnetization," susceptibility, and specific heat, studied via molecular dynamics simulations. Unlike conventional Ising models, we observe a striking divergence and sign change of the coefficient of thermal expansion near T_{c} caused by the coupling of flexural phonons to the buckled spin texture. We argue that a phenomenological model coupling Ising degrees of freedom to the flexural phonons in a thin elastic sheet can explain this unusual response.
受创建薄纳米级超材料以及理解原子级薄二元单层的努力所推动，我们研究了嵌入在可在三维空间中波动的独立二维晶体膜中的双稳态屈曲膨胀阵列的有限温度统计力学。屈曲节点的行为类似于离散但高度可压缩的伊辛自旋，通过分子动力学模拟研究，在(T_{c})处导致一个相变，其在交错“磁化强度”、磁化率和比热中出现奇点。与传统伊辛模型不同，我们观察到在(T_{c})附近热膨胀系数出现显著的发散和符号变化，这是由弯曲声子与屈曲自旋纹理的耦合引起的。我们认为，一个将伊辛自由度与薄弹性片中的弯曲声子耦合的唯象模型可以解释这种异常响应。
