Wang Yong, Wang Junjie, Yao Ge, Fan Zheyong, Granato Enzo, Kosterlitz Michael, Ala-Nissila Tapio, Car Roberto, Sun Jian
School of Physics and Collaborative Innovation Center of Advanced Microstructures, National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, China.
Department of Chemistry, Princeton University, Princeton, NJ 08544.
Proc Natl Acad Sci U S A. 2025 Apr 29;122(17):e2502980122. doi: 10.1073/pnas.2502980122. Epub 2025 Apr 21.
The nature of solid phases and cross-over of order-disorder phase transitions from two-dimensional (2D) layers to three-dimensional (3D) bulk in confined atomic systems remain largely unexplained. To this end, we consider noble gases and aluminum confined between graphene sheets at different pressures and temperatures. Using crystal structure search methods and molecular dynamics based on machine-learned potentials with quantum-mechanical accuracy, we identify structures of multilayer confined solids that deviate from simple close packing. Upon heating, we find that confined 2D monolayers melt according to the two-step continuous Kosterlitz-Thouless-Halperin-Nelson-Young theory. However, multilayer solids transition continuously into an intermediate layered-hexatic phase before melting discontinuously into an isotropic liquid. This intermediate phase persists at least up to 12 layers studied here. This change can be qualitatively understood based on the cross-over from 2D topological defects toward 3D ones during melting as the number of layers increases.
受限原子系统中固相的性质以及从二维（2D）层到三维（3D）体相的有序-无序相变的转变在很大程度上仍未得到解释。为此，我们考虑了在不同压力和温度下限制在石墨烯片之间的稀有气体和铝。使用基于具有量子力学精度的机器学习势的晶体结构搜索方法和分子动力学，我们确定了偏离简单密堆积的多层受限固体的结构。加热时，我们发现受限的二维单层根据两步连续的科斯特利茨- Thouless - 哈珀林 - 尼尔森 - 杨理论熔化。然而，多层固体在不连续地熔化为各向同性液体之前，会连续转变为中间层状六方相。这种中间相至少在此处研究的多达12层时持续存在。随着层数增加，这种变化可以基于熔化过程中从二维拓扑缺陷向三维拓扑缺陷的转变从定性上理解。
