向列极性物质中的相图、禁闭弦与一个新的普适类
Phase diagram, confining strings, and a new universality class in nematopolar matter
AI总结：
该研究构建向列序与极性序共存的最小模型，揭示三相相图、独特临界普适类及由恒定张力弦禁闭的拓扑缺陷对。
摘要：
我们研究了一个同时存在向列序和极性取向序的系统的最小模型，其中一个场倾向于有序，而另一个场更偏好各向同性。在强耦合条件下，有序场会使各向同性场取向，从而锁定二者的方向。相图揭示了三个不同的相——向列极性相（序相互对齐）、向列相（序相互独立）和各向同性相（序消失）——它们由连续和不连续相变分隔，其中包括一个三相点和一个三临界点。我们发现向列极性相—向列相相变具有独特的临界标度，不同于标准的向列或极性普适类。此外，在锁定的向列极性相中，我们证明向列 +1/2 拓扑缺陷对由具有恒定张力的弦连接并禁闭。这些弦源于锁定取向序时的阻挫，并可解释为 +1 极性拓扑缺陷的拉长核心。当足够强的背景场与极性序耦合时，所有拓扑缺陷都会被逐出该区域。解析预测得到了数值模拟的定量证实。
英文摘要：
We study a minimal model of a system with coexisting nematic and polar orientational orders, where one field tends to order and the other prefers isotropy. For strong coupling, the ordered field aligns the isotropic one, locking their orientations. The phase diagram reveals three distinct phases--nematopolar (aligned orders), nematic (independent orders), and isotropic (vanishing orders)--separated by continuous and discontinuous transitions, including a triple and a tricritical point. We find unique critical scaling for the nematopolar-nematic transition, distinct from standard nematic or polar universality classes. Additionally, in the locked nematopolar phase, we show nematic $+1/2$ topological defect pairs are connected and confined by strings with constant tension. These strings arise from frustration in locking the orientational orders and can be interpreted as elongated cores of $+1$ polar topological defects. When a sufficiently strong background field couples to the polar order, all topological defects are expelled from the region. Analytical predictions are quantitatively confirmed by numerical simulations.
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