理想非晶体：一种可能的新类有序物质，没有明显对称性破缺
Ideal noncrystals: A possible new class of ordered matter without apparent broken symmetry
AI总结：
发现二维理想非晶体，其无序但具有高秩序性，表现出晶体特性，且热力学有利，为有序物质新类别提供可能。
摘要：
秩序与无序是凝聚态物理和材料科学中两个基本且对立的主题。晶体被视为秩序的典范，以其长程平移秩序为特征。准晶体的发现，其表现出被晶体禁止的旋转对称性和无周期性，导致固态物理范式转变。进一步地，令人感兴趣的是，是否存在没有明显对称性破缺的有序物质？考虑如何有序的非晶（非晶体）固体的结构时，同样的问题再次出现。在这里，我们提出了二维理想非晶体的发现，它们在传统意义上是无序的，没有布拉格峰，但基于立体秩序，即它们是理想紧密排列的，表现出高秩序性。一种路径积分似的方法揭示了其底层的长程结构相关性。我们发现这些理想非晶体的特征是遵循德拜定律的声子振动模式，完全仿射的弹性响应，以及在较长波长下被抑制的密度波动，这类似于超均匀性——所有这些特征通常与晶体相关。因此，理想非晶体代表了一种奇特的物质形式，具有混合性质——非晶体但具有晶体般的性质。值得注意的是，这些状态被发现是热力学有利的，表明它们可能是一种新的有序物质类，没有明显对称性破缺。我们的发现显著扩展了有序物质状态的概念，并可能对熵驱动的有序性有更深入的理解，特别是在通用非晶材料中。
英文摘要：
Order and disorder constitute two fundamental and opposite themes in condensed matter physics and materials science. Crystals are considered the epitome of order, characterised by long-range translational order. The discovery of quasicrystals, which exhibit rotational symmetries forbidden in crystals and lack periodicity, led to a paradigm shift in solid-state physics. Moving one step forward, it is intriguing to ask whether ordered matter can exist without apparent symmetry breaking. The same question arises considering how ordered amorphous (noncrystalline) solids can be structured. Here, we present the discovery of ideal noncrystals in two dimensions, which are disordered in the conventional sense, lacking Bragg peaks, but exhibit high orderliness based on the steric order, i.e., they are ideally packed. A path-integral-like scheme reveals the underlying long-range structural correlation. We find that these ideal noncrystals are characterised by phononic vibrational modes following the Debye law, fully affine elastic responses, and suppressed density fluctuations at longer wavelengths, reminiscent of hyperuniformity -- all characteristics typically associated with crystals. Therefore, ideal noncrystals represent a peculiar form of matter with a mixed nature -- noncrystalline yet possessing crystal-like properties. Notably, these states are found to be thermodynamically favourable, indicating them as a possible new class of ordered matter without apparent symmetry breaking. Our findings significantly broaden the conceptualization of ordered states of matter and may contribute to a deeper understanding of entropy-driven ordering, particularly in generic amorphous materials.
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