Wang L, Yang C, Dove M T, Mokshin A V, Brazhkin V V, Trachenko K
School of Physics and Astronomy, Queen Mary University of London, Mile End Road, London, E1 4NS, UK.
Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai, 200240, China.
Sci Rep. 2019 Jan 24;9(1):755. doi: 10.1038/s41598-018-36178-6.
Physical properties of an interacting system are governed by collective excitations, but their nature at extreme supercritical conditions is unknown. Here, we present direct evidence for propagating solid-like longitudinal phonon-like excitations with wavelengths extending to interatomic separations deep in the supercritical state at temperatures up to 3,300 times the critical temperature. We observe that the crossover of dispersion curves develops at k points reducing with temperature. We interpret this effect as the crossover from the collective phonon to the collisional mean-free path regime of particle dynamics and find that the crossover points are close to both the inverse of the shortest available wavelength in the system and to the particle mean free path inferred from experiments and theory. Notably, both the shortest wavelength and mean free path scale with temperature with the same power law, lending further support to our findings.
相互作用系统的物理性质由集体激发决定，但其在极端超临界条件下的性质尚不清楚。在此，我们提供了直接证据，证明在高达临界温度3300倍的温度下，存在类似固体的纵向类声子激发，其波长延伸至超临界态深处的原子间距。我们观察到色散曲线的交叉在随温度降低的k点处出现。我们将此效应解释为从集体声子到粒子动力学的碰撞平均自由程 regime 的交叉，并发现交叉点既接近系统中最短可用波长的倒数，又接近从实验和理论推断出的粒子平均自由程。值得注意的是，最短波长和平均自由程都随温度以相同的幂律缩放，这进一步支持了我们的发现。
