Maire R, Plati A
Université Paris-Saclay, CNRS, Laboratoire de Physique des Solides, 91405 Orsay, France.
J Chem Phys. 2024 Aug 7;161(5). doi: 10.1063/5.0217958.
It has been recently shown that 2D systems can exhibit crystalline phases with long-range translational order showcasing a striking violation of the Hohenberg-Mermin-Wagner (HMW) theorem, which is valid at equilibrium. This is made possible by athermal driving mechanisms that inject energy into the system without exciting long wavelength modes of the density field, thereby inducing hyperuniformity. However, as thermal fluctuations are superimposed on the non-equilibrium driving, long-range translational order is inevitably lost. Here, we discuss the possibility of exploiting non-equilibrium effects to suppress arbitrarily large density fluctuations even when a global thermal bath is coupled to the system. We introduce a model of a harmonic crystal driven both by a global thermal bath and by a momentum conserving noise, where the typical observables related to density fluctuations and long-range translational order can be analytically derived and put in relation. This model allows us to rationalize the violation of the HMW theorem observed in previous studies through the prediction of large-wavelength phonons, which thermalize at a vanishing effective temperature when the global bath is switched off. The conceptual framework introduced through this theory is then applied to numerical simulations of a hard-disk solid in contact with a thermal bath and driven out-of-equilibrium by active collisions. Our numerical analysis demonstrates how varying driving and dissipative parameters can lead to an arbitrary enhancement of the quasi-long-range order in the system regardless of the applied global noise amplitude. Finally, we outline a possible experimental procedure to apply our results to a realistic granular system.
最近的研究表明，二维系统可以展现出具有长程平移序的晶相，这显著违背了在平衡态下有效的霍恩伯格 - 默明 - 瓦格纳（HMW）定理。这是通过非热驱动机制实现的，该机制在不激发密度场的长波长模式的情况下向系统注入能量，从而产生超均匀性。然而，由于热涨落在非平衡驱动之上叠加，长程平移序不可避免地丧失。在此，我们讨论利用非平衡效应来抑制任意大的密度涨落的可能性，即使全局热库与系统耦合时也是如此。我们引入一个由全局热库和动量守恒噪声共同驱动的简谐晶体模型，其中与密度涨落和长程平移序相关的典型可观测量可以通过解析推导得出并建立联系。这个模型使我们能够通过预测大波长声子来解释先前研究中观察到的对HMW定理的违背，当全局热库关闭时，这些声子在有效温度趋近于零时热化。通过该理论引入的概念框架随后被应用于与热库接触并通过主动碰撞驱动至非平衡态的硬磁盘固体的数值模拟。我们的数值分析表明，无论所施加的全局噪声幅度如何，改变驱动和耗散参数如何能够导致系统中准长程序的任意增强。最后，我们概述了一个将我们的结果应用于实际颗粒系统的可能实验步骤。
