动态压缩下成团和成条系统的结构转变和滞后现象
Structural Transitions and Hysteresis in Clump- and Stripe-Forming Systems Under Dynamic Compression
摘要：
利用数值模拟的方法，研究了二维空间中粒子通过竞争长程排斥和短程吸引相互作用的动力学演化。使用控制局部密度的与时间相关的准一维槽势来压缩颗粒，使系统经历一系列从低密度团簇晶格到条纹、空隙和高密度均匀状态的结构相变。压缩过程通过缓慢的弹性运动进行，当系统通过塑性重排坍塌到逐渐更高的密度时，这种弹性运动被雪崩般的活动爆发打断。塑性事件的大小不同，从小的颗粒重排，包括形成四极缺陷，大规模的涡和结构相变。在稠密均匀阶段，系统通过无序-有序过程介导的行减少过渡压缩。我们通过测量势能的变化，六重协调粒子的分数，局部密度和速度分布的重排事件的特征。在高约束下，我们发现幂律缩放的速度分布在行减少过渡。我们观察到滞后下的压缩时，相对较少的塑性重排发生逆转。解压缩系统表现出不同的相形态，并且当系统膨胀时与其被压缩时相比，在较低的压缩力下发生相变。
英文摘要：
Using numerical simulations, we study the dynamical evolution of particles interacting via competing long-range repulsion and short-range attraction in two dimensions. The particles are compressed using a time-dependent quasi-one dimensional trough potential that controls the local density, causing the system to undergo a series of structural phase transitions from a low density clump lattice to stripes, voids, and a high density uniform state. The compression proceeds via slow elastic motion that is interrupted with avalanche-like bursts of activity as the system collapses to progressively higher densities via plastic rearrangements. The plastic events vary in magnitude from small rearrangements of particles, including the formation of quadrupole-like defects, to large-scale vorticity and structural phase transitions. In the dense uniform phase, the system compresses through row reduction transitions mediated by a disorder-order process. We characterize the rearrangement events by measuring changes in the potential energy, the fraction of sixfold coordinated particles, the local density, and the velocity distribution. At high confinements, we find power law scaling of the velocity distribution during row reduction transitions. We observe hysteresis under a reversal of the compression when relatively few plastic rearrangements occur. The decompressing system exhibits distinct phase morphologies, and the phase transitions occur at lower compression forces as the system expands compared to when it is compressed.
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