AI 中文总结
研究在声悬浮粒子系综中，非互易多体相互作用如何激活其液态行为。通过声散射和微流产生非互易力，驱动粒子超扩散运动，经实验发现液滴运动粘度与水相似但界面张力极低，pinch-off 呈现独特轮廓，展现了该相互作用的特性。
AI 中文摘要
非互易力通常是相互作用物体性质不对称的结果。然而，即使所有物体相同且各向同性，且两物体间的成对相互作用完全互易，当许多物体的排列在非成对多体相互作用下打破构型对称时，非互易力仍会出现。本文证明这种涌现的非互易性可激活粒子系综表现得像液体，不过有独特特性。实验中，被动微球在空气中声悬浮，形成含数百个粒子的自由漂浮单层，集体表现像二维液滴。粒子通过声散射和声音诱导粘性微流共同产生的非互易多体力相互作用。发现这些力驱动粒子超扩散运动，速度分布有非高斯尾部。用侧向伸进悬浮平面的探针进行液滴悬垂和 pinch-off 实验。与普通液体相比，液滴运动粘度与水相似，但界面张力极低。pinch-off 由非互易诱导的主动涨落驱动，呈现出与接近破裂的液体纳米喷流中类似的自相似双锥颈轮廓，不过这里由幂律行为表征，标度指数异常小。
英文摘要
Nonreciprocal forces are often a consequence of asymmetry in the properties of the interacting objects. However. even if all objects are identical and isotropic, and the pairwise interactions between two objects are completely reciprocal, nonreciprocal forces can still appear when an arrangement of many objects breaks configurational symmetry in the presence of non-pairwise, multi-body interactions. Here we demonstrate that such emergent nonreciprocity can activate a particle ensemble to behave like a liquid, albeit with unique traits. In our experiments, passive microspheres are acoustically levitated in air, where they form a freely floating monolayer containing up to a couple hundred particles and collectively behave like a two-dimensional liquid droplet. The particles interact via nonreciprocal multi-body forces that arise from the combination of acoustic scattering and sound-induced viscous microstreaming. We find that these forces drive superdiffusive particle motion with non-Gaussian tails in the particles' speed distribution. Using probes that reach laterally into the levitation plane, we perform liquid pendant drop and pinch-off experiments. Compared to ordinary liquids, the droplets are found to have a kinematic viscosity similar to that of water, but in combination with an extremely low interfacial tension. The pinching-off is driven by nonreciprocity-induced active fluctuations and exhibits the self-similar double-cone neck profile seen also in liquid nanojets close to rupture, however here characterized by power law behavior with a scaling exponent that is anomalously small.
